Publications by authors named "Bénédicte M A Delattre"

28 Publications

  • Page 1 of 1

Relaxation time of brain tissue in the elderly assessed by synthetic MRI.

Brain Behav 2021 Dec 4:e2449. Epub 2021 Dec 4.

Division of Neuroradiology, Department of Diagnostics, Geneva University Hospitals, Geneva, Switzerland.

Background: Synthetic MRI (SyMRI) is a quantitative technique that allows measurements of T1 and T2 relaxation times (RTs). Brain RT evolution across lifespan is well described for the younger population. The aim was to study RTs of brain parenchyma in a healthy geriatric population in order to define the normal value of structures in this group population. Normal values for geriatric population could help find biomarker for age-related brain disease.

Materials And Methods: Fifty-four normal-functioning individuals (22 females, 32 males) with mean age of 83 years (range 56-98) underwent SyMRI. RT values in manually defined ROIs (centrum semiovale, middle cerebellar peduncles, thalamus, and insular cortex) and in segmented whole-brain components (brain parenchyma, gray matter, white matter, myelin, CSF, and stromal structures) were extracted from the SyMRI segmentation software. Patients' results were combined into the group age. Main ROI-based and whole-brain results were compared for the all dataset and for age group results as well.

Results: For white matter, RTs between ROI-based analyses and whole-brain results for T2 and for T1 were statistically different and a trend of increasing T1 in centrum semiovale and cerebellar peduncle was observed. For gray matter, thalamic T1 was statistically different from insular T1. A difference was also found between left and right insula (p < .0001). T1 RTs of ROI-based and whole-brain-based analyses were statistically different (p < .0001). No significant difference in T1 and T2 was found between age groups on ROI-based analysis, but T1 in centrum semiovale and thalamus increased with age. No statistical difference between age groups was found for the various segmented volumes except for myelin between 65-74 years of age and the 95-105 years of age groups (p = .038).

Conclusions: SyMRI is a new tool that allows faster imaging and permits to obtain quantitative T1 and T2. By defining RT values of different brain components of normal-functioning elderly individuals, this technique may be used as a biomarker for clinical disorders like dementia.
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http://dx.doi.org/10.1002/brb3.2449DOI Listing
December 2021

Comparing dynamic susceptibility contrast perfusion post-processing with different clinically available software among patients affected of a high-grade glioma.

J Neuroradiol 2020 Oct 13. Epub 2020 Oct 13.

Unité de Neuroradiologie Diagnostique, Hôpitaux Universitaires de Genève, Faculté de Médecine de Genève, Rue Gabrielle-Perret-Gentil 4, 1205 Genève, Suisse. Electronic address:

Background And Purpose: The main purpose of this retrospective study was to evaluate inter-software variability in patients affected of a high-grade glioma for the post-processing of dynamic susceptibility contrast (DSC) perfusion imaging in MRI. MATERIALS AND METHODS: The included patients were either anaplastic astrocytoma (WHO grade III) or glioblastoma (WHO grade IV) located in the cerebral parenchyma. The postprocessing of 54 MRI-DSC imaging from 46 patients using both Intellispace© (Philips) and Olea© (Olea Medical) software was performed. The hemodynamic parameter studied was the normalised relative cerebral blood volume corrected for the T1 leakage effect (nrCBVc). The inter-operator variabilities were also evaluated.

Results: Regarding inter-software reproducibility, Cohen's Kappa from therapeutic follow-up obtained were 0.61, close to the recommended limit (0.60). Subgroups were created to complete the analysis and to evaluate the partial volume effect. Even if necrosis or vascular structures from regions of interest (ROI) were avoided, results did not improve. ROI of a minimum area of 250 mm yielded a Cohen's Kappa of 0.65. The inter-operator reproducibility on Intellispace and Olea were 0.90 and 0.73 respectively, which is satisfactory.

Conclusion: The reproducibility between Intellispace and Olea was below recommended threshold in a clinical context. This discrepancy can be explained by the partial volume effect and the models used. ROI with an area of at least 250 mm improves this reproducibility and becomes acceptable.
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http://dx.doi.org/10.1016/j.neurad.2020.09.010DOI Listing
October 2020

Quantitative magnetic resonance imaging: differentiating soft tissue implants and fillers used in cosmetic and reconstructive surgery.

Skeletal Radiol 2021 Jan 5;50(1):231-237. Epub 2020 Aug 5.

Diagnostic Department, Division of Radiology, Geneva University Hospital, Rue Gabrielle-Perret-Gentil 4, 1211, Geneva 14, Switzerland.

Objective: To evaluate the value of synthetic magnetic resonance imaging (MRI) and T2 mapping in distinguishing between different types of fillers in soft tissues.

Materials And Methods: Ex vivo fillers of buttock soft tissues (silicone, collagen, and different types of hyaluronic acid) were scanned using a synthetic MRI sequence at 1.5 and 3 T and an optimized T2 mapping sequence to measure the T2 relaxation times of the fillers ex vivo. Three patients addressed to assess complications with buttock fillers underwent MRI with the standard morphological sequences and an additional synthetic MRI sequence; T2 mapping was not performed for the patients. Two patients had silicone fillers, whereas the exact filler composition for the third patient was unknown.

Results: Measurements of T1 and T2 relaxation times of ex vivo fillers at 1.5 and 3 T using synthetic MRI showed that the silicone, collagen, and hyaluronic acid had distinct relaxation time characteristics. In vivo, the synthetic MRI correctly identified silicone in the two patients with known silicone fillers, showing low T1 and T2 values, whereas in the third patient with an unknown filler type, the synthetic MRI suggested a collagen filler, with intermediate relaxation time values.

Conclusion: Quantitative sequences have the potential to differentiate between filler types in a noninvasive fashion.
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http://dx.doi.org/10.1007/s00256-020-03564-zDOI Listing
January 2021

Every second retired elite female football player has MRI evidence of knee osteoarthritis before age 50 years: a cross-sectional study of clinical and MRI outcomes.

Knee Surg Sports Traumatol Arthrosc 2020 Feb 17;28(2):353-362. Epub 2019 Jun 17.

Department of Orthopaedic Surgery and Traumatology, University Hospital of Geneva, Geneva, Switzerland.

Purpose: To assess knee health in retired female football players, using magnetic resonance imaging (MRI) and self-report. The focus of analysis were degenerative changes of the tibiofemoral joint, and their relationship to osteoarthritis symptoms and previous knee injury.

Methods: Forty-nine retired elite, female football players (98 knees) aged 37 years on average participated. Tibiofemoral cartilage and meniscus status of both knees were evaluated using MRI and graded according to modified Outerbridge and Stoller classifications, respectively. Symptoms were assessed through a standardised questionnaire (Knee Osteoarthritis Outcome Score: KOOS). Knee injury history was recorded via a semi-structured interview. To investigate how injury variables relate to outcomes, binary logistic regression models were used and reported with odds ratios (OR).

Results: Fifty-one per cent of players (n = 25) fulfilled the MRI criterion for knee osteoarthritis, 69.4% (n = 34) had substantial meniscal loss and 59.6% (n = 28) reported substantial clinical symptoms. Chondral- and meniscal loss were associated with significantly lower scores on three of five KOOS subscales (p < .05). Both chondral and meniscal loss were significantly predicted by previous traumatic knee injury (OR = 4.6, OR = 2.6), the injury affecting the non-striking leg (OR = 8.6, OR = 10.6) and type of injury; participants with combined ACL/meniscus injuries had the highest risk for substantial chondral and meniscal loss (OR = 14.8, OR = 9.5). Chondral loss was significantly predicted by isolated meniscus injury treated with partial meniscectomy (OR = 5.4), but not by isolated reconstructed ACL injury. Clinical symptoms were only significantly predicted by previous traumatic knee injury (OR = 5.1).

Conclusions: Serious degenerative changes were found in a high number of retired female football players' knees 10 years after their career. Meniscal integrity is key for knee osteoarthritis outcomes in young adults, and thus, its preservation should be a priority.
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http://dx.doi.org/10.1007/s00167-019-05560-wDOI Listing
February 2020

Neurovascular stent artifacts in 3D-TOF and 3D-PCMRI: Influence of stent design on flow measurement.

Magn Reson Med 2019 01 12;81(1):560-572. Epub 2018 Jun 12.

Departement of Neuroradiology, Geneva University Hospitals, Geneva, Switzerland.

Purpose: The morphological and hemodynamic evaluations of neurovascular diseases treated with stents would benefit from noninvasive imaging techniques such as 3D time-of-flight MRI (3D-TOF) and 3D phase contrast MRI (3D-PCMRI). For this purpose, a comprehensive evaluation of the stent artifacts and their impact on the flow measurement is critical.

Methods: The artifacts of a representative sample of neurovascular stents were evaluated in vitro with 3D-TOF and 3D-PCMRI sequences. The dependency of the artifacts with respect to the orientation was analyzed for each stent design as well as the impact on the flow measurement accuracy. Furthermore, the 3D-PCMRI data of four patients carrying intracranial aneurysms treated with flow diverter stents were analyzed as illustrative examples.

Results: The stent artifacts were mainly confined to the stent lumen therefore indicating the leading role of shielding effect. The influence of the stent design and its orientation with respect to the transmitting MR coils were highlighted. The artifacts impacted the 3D-PCMRI velocities mainly in the low magnitude domains, which were discarded from the analysis ensuring reliable near-stent velocities. The feasibility of in-stent flow measurements was confirmed in vivo on two patients who showed strong correlation between flow and geometric features. In two other patients, the consistency of out-of-stent velocities was verified qualitatively through intra-aneurysmal streamlines except when susceptibility artifacts occurred.

Conclusion: The present results motivate the conception of low inductance or nonconductive stent design. Furthermore, the feasibility of near-stent 3D-PCMRI measurements opens the door to clinical applications like the post-treatment follow-up of stenoses or intracranial aneurysms.
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http://dx.doi.org/10.1002/mrm.27352DOI Listing
January 2019

Local recurrence of squamous cell carcinoma of the head and neck after radio(chemo)therapy: Diagnostic performance of FDG-PET/MRI with diffusion-weighted sequences.

Eur Radiol 2018 Feb 15;28(2):651-663. Epub 2017 Aug 15.

Department of Imaging, Divisions of Radiology and Nuclear Medicine, Geneva University Hospitals, University of Geneva, Rue, Gabrielle Perret Gentil 4, CH-1211, Geneva 14, Switzerland.

Purpose: To determine the diagnostic performance of FDG-PET/MRI with diffusion-weighted imaging (FDG-PET/DWIMRI) for detection and local staging of head and neck squamous cell carcinoma (HNSCC) after radio(chemo)therapy.

Materials And Methods: This was a prospective study that included 74 consecutive patients with previous radio(chemo)therapy for HNSCC and in whom tumour recurrence or radiation-induced complications were suspected clinically. The patients underwent hybrid PET/MRI examinations with morphological MRI, DWI and FDG-PET. Experienced readers blinded to clinical/histopathological data evaluated images according to established diagnostic criteria taking into account the complementarity of multiparametric information. The standard of reference was histopathology with whole-organ sections and follow-up ≥24 months. Statistical analysis considered data clustering.

Results: The proof of diagnosis was histology in 46/74 (62.2%) patients and follow-up (mean ± SD = 34 ± 8 months) in 28/74 (37.8%). Thirty-eight patients had 43 HNSCCs and 46 patients (10 with and 36 without tumours) had 62 benign lesions/complications. Sensitivity, specificity, and positive and negative predictive value of PET/DWIMRI were 97.4%, 91.7%, 92.5% and 97.1% per patient, and 93.0%, 93.5%, 90.9%, and 95.1% per lesion, respectively. Agreement between imaging-based and pathological T-stage was excellent (kappa = 0.84, p < 0.001).

Conclusion: FDG-PET/DWIMRI yields excellent results for detection and T-classification of HNSCC after radio(chemo)therapy.

Key Points: • FDG-PET/DWIMRI yields excellent results for the detection of post-radio(chemo)therapy HNSCC recurrence. • Prospective one-centre study showed excellent agreement between imaging-based and pathological T-stage. • 97.5% of positive concordant MRI, DWI and FDG-PET results correspond to recurrence. • 87% of discordant MRI, DWI and FDG-PET results correspond to benign lesions. • Multiparametric FDG-PET/DWIMRI facilitates planning of salvage surgery in the irradiated neck.
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http://dx.doi.org/10.1007/s00330-017-4999-1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5740208PMC
February 2018

Fat suppression techniques for breast MRI: Dixon versus spectral fat saturation for 3D T1-weighted at 3 T.

Radiol Med 2017 Oct 22;122(10):731-742. Epub 2017 Jun 22.

Radiology Department, Geneva University Hospital, Rue Gabrielle-Perret-Gentil 4, 1205, Geneva, Switzerland.

Objective: To compare two fat suppression techniques used for 3D T1-weighted sequence in breast MRI (magnetic resonance imaging), namely Dixon versus spectral fat saturation (fat sat).

Materials And Methods: All breast MRI examinations performed in a Philips 3 T unit between March 2013 and October 2015 including either a Dixon or a fat sat sequence were retrospectively analyzed. The examinations were subjectively evaluated by two independent experienced readers in a scale of 5 for overall quality of fat suppression, homogeneity of fat suppression, definition of anatomic structures and focal lesions, diagnostic confidence for axillary and internal mammary regions and the presence of artifacts, 1 corresponding to excellent and 5 to non-diagnostic quality. Contrast-to-noise-ratio (CNR) measurements for muscle and focal lesions were also performed.

Results: Overall 161 women (mean age 51.6 ± 12.0 years) underwent 189 MR examinations, 113 with the fat saturation and 76 with the Dixon sequence. Interobserver variability was good (kappa = 0.757). In all subjectively evaluated parameters, the Dixon sequence was superior to the fat sat (p < 0.05). Mean values of CNR for muscle and focal lesions were 9.98 (±4.2), 17.9 (±7.53) for the fat sat and 18.3 (±10.4) and 29.3 (±14.1) for the Dixon sequence, respectively (p < 0.001).

Conclusion: 3D T1 Dixon sequence is superior to fat sat for dedicated breast MRI at 3 T, in terms of efficiency of fat suppression and image quality with the added advantage of optimal exploration of the axillary areas.
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http://dx.doi.org/10.1007/s11547-017-0782-2DOI Listing
October 2017

3D phase contrast MRI: Partial volume correction for robust blood flow quantification in small intracranial vessels.

Magn Reson Med 2018 Jan 28;79(1):129-140. Epub 2017 Feb 28.

Division of Neuroradiology, Geneva University Hospitals & Faculty of Medicine, University of Geneva, Geneva, Switzerland.

Purpose: Recent advances in 3D-PCMRI (phase contrast MRI) sequences allow for measuring the complex hemodynamics in cerebral arteries. However, the small size of these vessels vs spatial resolution can lead to non-negligible partial volume artifacts, which must be taken into account when computing blood flow rates. For this purpose, we combined the velocity information provided by 3D-PCMRI with vessel geometry measured with 3DTOF (time of flight MRI) or 3DRA (3D rotational angiography) to correct the partial volume effects in flow rate assessments.

Methods: The proposed methodology was first tested in vitro on cylindrical and patient specific vessels subject to fully controlled pulsatile flows. Both 2D- and 3D-PCMRI measurements using various spatial resolutions ranging from 20 to 1.3 voxels per vessel diameter were analyzed and compared with flowmeter baseline. Second, 3DTOF, 2D- and 3D-PCMRI measurements were performed in vivo on 35 patients harboring internal carotid artery (ICA) aneurysms indicated for endovascular treatments requiring 3DRA imaging.

Results: The in vitro 2D- and 3D-PCMRI mean flow rates assessed with partial volume correction showed very low sensitivity to the acquisition resolution above ≈2 voxels per vessel diameter while uncorrected flow rates deviated critically when decreasing the spatial resolution. 3D-PCMRI flow rates measured in vivo in ICA agreed very well with 2D-PCMRI data and a good flow conservation was observed at the C7 bifurcation. Globally, partial volume correction led to 10-15% lower flow rates than uncorrected values as those reported in most of the published studies on intracranial flows.

Conclusion: Partial volume correction may improve the accuracy of PCMRI flow rate measurements especially in small vessels such as intracranial arteries. Magn Reson Med 79:129-140, 2018. © 2017 International Society for Magnetic Resonance in Medicine.
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http://dx.doi.org/10.1002/mrm.26637DOI Listing
January 2018

FDG PET/MR Imaging in Major Neurocognitive Disorders.

Curr Alzheimer Res 2017 ;14(2):186-197

Geneva University and University Hospital, Rue Gabrielle Perret Gentil 4, 1205 Geneva, Switzerland.

PET/MRI tomographs represent the latest development in hybrid molecular imaging, opening new perspectives for clinical and research applications and attracting a large interest among the medical community. This new hybrid modality is expected to play a pivotal role in a number of clinical applications and among these the assessment of neurodegenerative disorders. PET and MRI, acquired separately, are already the imaging biomarkers of choice for a comprehensive assessment of the changes occurring in dementias (major cognitive disorders) as well as in their prodromal phase. In this paper we review the current evidence on the use of integrated PET/MRI scanners to investigate patients with neurodegenerative conditions, and in particular major neurocognitive disorders. The number of studies performed is still limited and shows that the use of PET/MRI gives results overall comparable to PET/CT and MRI acquired independently. We also address the challenges for quantitative aspects in PET/MRI, namely attenuation, partial volume and motion correction and the use of semi-quantitative approaches for FDG PET image analysis in this framework. The recent development of PET tracers for the in vivo differential diagnosis of dementias, able to visualize amyloid and tau deposits, suggests that in the future PET/MRI might represent the investigation of choice for a single session evaluation of morphological, functional and molecular markers.
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http://dx.doi.org/10.2174/1567205013666160620115130DOI Listing
October 2017

Diffusion in prostate cancer detection on a 3T scanner: How many b-values are needed?

J Magn Reson Imaging 2016 09 23;44(3):601-9. Epub 2016 Feb 23.

Division of Radiology, Geneva University Hospitals, Geneva, Switzerland.

Purpose: To assess the influence of perfusion on apparent coefficient diffusion (ADC) maps, the contribution of b-value images, and the number of b-values needed in prostate cancer detection by diffusion-weighted imaging (DWI).

Materials And Methods: Patients scheduled for prostatectomy were scanned by 3T magnetic resonance imaging (MRI) with DWI based on b-values 0-500-1000-1500 s/mm(2) . A monoexponential model was fitted to obtain ADC using multiple b-values, with or without b0 (perfusion-sensitive ADC4b-b0-500-1000-1500 , perfusion-insensitive ADC3b-b500-1000-1500 ), or two b-values (ADC2b-b0-500 , ADC2b-b0-1000 , ADC2b-b0-1500 ). Prostate and cancer foci were segmented to label voxels as normal or tumoral, according to histology. Areas under receiver operating characteristic curves (AUC) were calculated for each ADC and b-value, then for multivariate logistic regression models combining them. A threshold of 85 tumoral voxels (=0.5 cm(3) ) was used to stratify AUC analysis.

Results: In all, 21 patients were selected. Segmentation collected 143,665 prostatic voxels including 10,069 tumoral voxels. In five patients, tumor segmentation provided fewer than 85 voxels, resulting in an ADC with AUC inferior to 0.52. In 16 patients with larger tumors, perfusion-sensitive ADC4b-b0-500-1000-1500 performed better than perfusion-insensitive ADC3b-b500-1000-1500 and similar to ADC2b-b0-1500 (AUC of 0.840, 0.809, and 0.838, respectively). In comparison to the ADC alone, models combining ADC4b-b0-500-1000-1500 or ADC2b-b0-1500 with b1500 improved performance, leading to similar AUCs of 0.884 and 0.883, respectively. In both models, ADC and b1500 were significant markers (P < 0.001).

Conclusion: Including b0 in ADC calculation provided superior ADC maps for prostate cancer detection. b1500 images as a combined parameter with ADC also improved performance. Using more than two b-values showed no improvement. J. Magn. Reson. Imaging 2016;44:601-609.
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http://dx.doi.org/10.1002/jmri.25206DOI Listing
September 2016

Clinical utility of 18F-FDG-PET/MR for preoperative breast cancer staging.

Eur Radiol 2016 Jul 17;26(7):2297-307. Epub 2015 Oct 17.

Department of Imaging, Division of Nuclear Medicine, Geneva University Hospital, Rue Gabrielle-Perret-Gentil 4, 1205, Geneva, Switzerland.

Objective: To evaluate the performance of 18F-fluorodeoxyglucose (FDG) positron emission tomography magnetic resonance imaging (PET/MR) for preoperative breast cancer staging.

Methods: Preoperative PET/MR exams of 58 consecutive women with breast cancer were retrospectively reviewed. Histology and mean follow-up of 26 months served as gold standard. Four experienced readers evaluated primary lesions, lymph nodes and distant metastases with contrast-enhanced MRI, qualitative/quantitative PET, and combined PET/MR. ROC curves were calculated for all modalities and their combinations.

Results: The study included 101 breast lesions (83 malignant, 18 benign) and 198 lymph node groups, (34 malignant, 164 benign). Two patients had distant metastases. Areas under the curve (AUC) for breast cancer were 0.9558, 0.8347 and 0.8855 with MRI, and with qualitative and quantitative PET/MR, respectively (p = 0.066). Sensitivity for primary cancers with MRI and quantitative PET/MR was 100 % and 77 % (p = 0.004), and for lymph nodes 88 % and 79 % (p = 0.25), respectively. Specificity for MRI and PET/MR for primary cancers was 67 % and 100 % (p = 0.03) and for lymph nodes 98 % and 100 % (p = 0.25).

Conclusions: In breast cancer patients, MRI alone has the highest sensitivity for primary tumours. For nodal metastases, both MRI and PET/MR are highly specific.

Key Points: • MRI alone and PET/MR have a similar overall diagnostic performance. • MRI alone has a higher sensitivity than PET/MR for local tumour assessment. • Both MRI and PET/MR have a limited sensitivity for nodal metastases. • Positive lymph nodes on MRI or PET/MR do not require presurgical biopsy.
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http://dx.doi.org/10.1007/s00330-015-4054-zDOI Listing
July 2016

In vivo free-breathing DTI and IVIM of the whole human heart using a real-time slice-followed SE-EPI navigator-based sequence: A reproducibility study in healthy volunteers.

Magn Reson Med 2016 07 24;76(1):70-82. Epub 2015 Aug 24.

CREATIS; CNRS (UMR 5220); INSERM (U1044); INSA Lyon; Université de Lyon, Lyon, France.

Purpose: In this study, we proposed an efficient free-breathing strategy for rapid and improved cardiac diffusion-weighted imaging (DWI) acquisition using a single-shot spin-echo echo planar imaging (SE-EPI) sequence.

Methods: A real-time slice-following technique during free-breathing was combined with a sliding acquisition-window strategy prior Principal Component Analysis temporal Maximum Intensity Projection (PCAtMIP) postprocessing of in-plane co-registered diffusion-weighted images. This methodology was applied to 10 volunteers to quantify the performance of the motion correction technique and the reproducibility of diffusion parameters.

Results: The slice-following technique offers a powerful head-foot respiratory motion management solution for SE-EPI cDWI with the advantage of a 100% duty cycle scanning efficiency. The level of co-registration was further improved using nonrigid motion corrections and was evaluated with a co-registration index. Vascular fraction f and the diffusion coefficients D and D* were determined to be 0.122 ± 0.013, 1.41 ± 0.09 × 10(-3) mm(2) /s and 43.6 ± 9.2 × 10(-3) mm(2) /s, respectively. From the multidirectional dataset, the measured mean diffusivity was 1.72 ± 0.09 × 10(-3) mm(2) /s and the fractional anisotropy was 0.36 ± 0.02.

Conclusion: The slice-following DWI SE-EPI sequence is a promising solution for clinical implementation, offering a robust improved workflow for further evaluation of DWI in cardiology. Magn Reson Med 76:70-82, 2016. © 2015 Wiley Periodicals, Inc.
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http://dx.doi.org/10.1002/mrm.25852DOI Listing
July 2016

Hybrid PET/MRI as a tool to detect brown adipose tissue: Proof of principle.

Obes Res Clin Pract 2015 Nov-Dec;9(6):613-7. Epub 2015 Jun 4.

Nuclear Medicine and Molecular Unit, Department of Medical Imaging, Geneva University Hospital and Faculty of Medicine, Geneva, Switzerland.

Objective: The purpose of this study was to assess the performance of (18)F-FDG hybrid PET/MRI to detect and localise the presence of metabolically active brown adipose tissue (BAT).

Methods: We retrospectively analyzed 197 consecutive (18)F-flurodeoxyglucose ((18)F-FDG) positron-emission tomographic (PET) and magnetic resonance imaging (MRI) images performed with a hybrid whole-body PET-MRI tomography in 192 patients. These patients were originally investigated mainly for oncological staging, in the absence of a cooling protocol. The presence of BAT was defined as a soft tissue structure that was larger than 4mm in diameter, had the characteristics of fat tissue on MRI and had a maximal standardised uptake value (SUV) of (18)F-FDG of at least 2.0. No specific MRI sequences for BAT detection were acquired.

Results: PET/MRI identified the presence of metabolically active BAT in 5 out of 192 patients (2.6%). BAT positive subjects were all female, significantly younger and with significantly lower body weight than BAT negative subjects.

Conclusions: Whole body hybrid PET/MRI allowed for the identification of BAT, with a low prevalence, comparable to previous retrospective PET/CT studies realised in the absence of a cooling protocol. The main advantages of the PET/MRI hybrid technique, as compared with PET/CT, includes a lower radiation burden, and the possibility to combine a multiparameter fat characterization by dedicated MRI sequences. Hybrid PET/MRI might represent the ideal tool for BAT evaluation.
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http://dx.doi.org/10.1016/j.orcp.2015.05.004DOI Listing
September 2016

PET/MR in Breast Cancer.

Semin Nucl Med 2015 Jul;45(4):304-21

Service de Médecine Nucléaire, Hôpitaux Universitaires de Genève, rue Gabrielle-Perret-Gentil, Genève, Switzerland. Electronic address:

Breast cancer is an international public health concern in which an optimal treatment plan requires a precise staging. Both MRI and PET imaging techniques have made significant progress in the last decades with constant improvements that made both modalities clinically relevant in several stages of breast cancer management and follow-up. On one hand, specific breast MRI permits high diagnostic accuracy for local tumor staging, and whole-body MRI can also be of great use in distant staging, eventually accompanied by organ-specific MRI sequences. Moreover, many different MRI sequences can be performed, including functional MRI, letting us foresee important improvements in breast cancer characterization in the future. On the contrary, (18)F-FDG-PET has a high diagnostic performance for the detection of distant metastases, and several other tracers currently under development may profoundly affect breast cancer management in the future with better determination of different types of breast cancers allowing personalized treatments. As a consequence PET/MR is a promising emerging technology, and it is foreseeable that in cases where both PET and MRI data are needed, a hybrid acquisition is justified when available. However, at this stage of deployment of such hybrid scanners in a clinical setting, more data are needed to demonstrate their added value beyond just patient comfort of having to undergo a single examination instead of two, and the higher confidence of diagnostic interpretation of these co-registered images. Optimized imaging protocols are still being developed and are prone to provide more efficient hybrid protocols with a potential improvement in diagnostic accuracy. More convincing studies with larger number of patients as well as cost-effectiveness studies are needed. This article provides insights into the current state-of-the-art of PET/MR in patients with breast cancer and gives an outlook on future developments of both imaging techniques and potential applications in the future.
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http://dx.doi.org/10.1053/j.semnuclmed.2015.03.003DOI Listing
July 2015

All-in-one interictal presurgical imaging in patients with epilepsy: single-session EEG/PET/(f)MRI.

Eur J Nucl Med Mol Imaging 2015 Jun 17;42(7):1133-43. Epub 2015 Apr 17.

Department of Radiology and Medical Informatics, Geneva University Hospital, 1211, Geneva 14, Switzerland.

Purpose: In patients with pharmacoresistant focal epilepsy, resection of the epileptic focus can lead to freedom from seizures or significant improvement in well-selected candidates. Localization of the epileptic focus with multimodal concordance is crucial for a good postoperative outcome. Beyond the detection of epileptogenic lesions on structural MRI and focal hypometabolism on FDG PET, EEG-based Electric Source Imaging (ESI) and simultaneous EEG and functional MRI (EEG-fMRI) are increasingly applied for mapping epileptic activity. We here report presurgical multimodal interictal imaging using a hybrid PET/MR scanner for single-session FDG PET, MRI, EEG-fMRI and ESI.

Methods: This quadrimodal imaging procedure was performed in a single session in 12 patients using a high-density (256 electrodes) MR-compatible EEG system and a hybrid PET/MR scanner. EEG was used to exclude subclinical seizures during uptake of the PET tracer, to compute ESI on interictal epileptiform discharges and to guide fMRI analysis for mapping haemodynamic changes correlated with interictal epileptiform activity.

Results: The whole multimodal recording was performed in less than 2 hours with good patient comfort and data quality. Clinically contributory examinations with at least two modalities were obtained in nine patients and with all modalities in five patients.

Conclusion: This single-session quadrimodal imaging procedure provided reliable and contributory interictal clinical data. This procedure avoids multiple scanning sessions and is associated with less radiation exposure than PET-CT. Moreover, it guarantees the same medication level and medical condition for all modalities. The procedure improves workflow and could reduce the duration and cost of presurgical epilepsy evaluations.
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http://dx.doi.org/10.1007/s00259-015-3045-2DOI Listing
June 2015

90Yttrium PET/MR-based dosimetry after liver radioembolization (SIRT).

Clin Nucl Med 2015 Apr;40(4):355-7

From the *Departments of Nuclear Medicine, and †Radiology, Hôpitaux Universitaires de Genève, Geneva, Switzerland.

Biodistribution and dosimetric aspects are important issues in the preparation realization of radionuclide therapies and thus play an emerging role in radioembolization of liver malignancies. Biodistribution assessment of liver selective internal radiotherapy (SIRT) has been shown feasible using PET/CT PET/magnetic resonance (MR). Whereas prospective dosimetry using 99mTc macroaggregated albumin SPECT/CT is discussed controversially, retrospective 90Y PET/CT has been shown feasible for dosimetry of SIRT in recent studies. Considering the advantages of PET/MR with regard to lesion detection radiation dose reduction compared to PET/CT, especially when repeated scanning is intended, we investigated the use of PET/MR for dosimetry of liver SIRT.
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http://dx.doi.org/10.1097/RLU.0000000000000713DOI Listing
April 2015

Assessment of intra-aneurysmal flow modification after flow diverter stent placement with four-dimensional flow MRI: a feasibility study.

J Neurointerv Surg 2015 Dec 3;7(12):913-9. Epub 2014 Oct 3.

Division of Neuroradiology, Department of Medical Imaging, University Hospitals of Geneva, Geneva, Switzerland.

Background: Flow diverter stents (FDS) have been effectively used for the endovascular treatment of sidewall intracranial aneurysms (IAs). Unlike standard endovascular treatments used to exclude directly the aneurysm bulge from the parent vessel, FDS induce reduction in the intra-aneurysmal flow and promote progressive and stable thrombosis therein. The advent of FDS has therefore increased the need for understanding of IA hemodynamics.

Methods: We proposed the use of the most recently evolved four-dimensional (4D) flow MRI technique to evaluate qualitatively and quantitatively post-FDS flow modification in 10 patients. We report intra-aneurysmal velocity measurements and the influence of metal artifacts induced by the stent.

Results: An index was defined to quantitatively measure flow changes-namely, the proportional velocity reduction ratio (PVRR)-with ranges from 34.6% to 71.1%. Furthermore, we could compare streamlines characterizing the post-stent flow patterns in five patients in whom the intra-aneurysmal velocity was beyond the visualization threshold of 7.69 cm/s.

Conclusions: Despite metal artifacts and the low velocities involved, 4D flow MRI could be of interest to measure qualitatively and quantitatively flow changes in stented aneurysms. However, further enhancements are required together with further validation work before it can be considered for clinical use.
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http://dx.doi.org/10.1136/neurintsurg-2014-011348DOI Listing
December 2015

Free-breathing diffusion tensor imaging and tractography of the human heart in healthy volunteers using wavelet-based image fusion.

IEEE Trans Med Imaging 2015 Jan 10;34(1):306-16. Epub 2014 Sep 10.

Free-breathing cardiac diffusion tensor imaging (DTI) is a promising but challenging technique for the study of fiber structures of the human heart in vivo. This work proposes a clinically compatible and robust technique to provide three-dimensional (3-D) fiber architecture properties of the human heart. To this end, 10 short-axis slices were acquired across the entire heart using a multiple shifted trigger delay (TD) strategy under free breathing conditions. Interscan motion was first corrected automatically using a nonrigid registration method. Then, two post-processing schemes were optimized and compared: an algorithm based on principal component analysis (PCA) filtering and temporal maximum intensity projection (TMIP), and an algorithm that uses the wavelet-based image fusion (WIF) method. The two methods were applied to the registered diffusion-weighted (DW) images to cope with intrascan motion-induced signal loss. The tensor fields were finally calculated, from which fractional anisotropy (FA), mean diffusivity (MD), and 3-D fiber tracts were derived and compared. The results show that the comparison of the FA values (FA(PCATMIP) = 0.45 ±0.10, FA(WIF) = 0.42 ±0.05, P=0.06) showed no significant difference, while the MD values ( MD(PCATMIP)=0.83 ±0.12×10(-3) mm (2)/s, MD(WIF)=0.74±0.05×10(-3) mm (2)/s, P=0.028) were significantly different. Improved helix angle variations through the myocardium wall reflecting the rotation characteristic of cardiac fibers were observed with WIF. This study demonstrates that the combination of multiple shifted TD acquisitions and dedicated post-processing makes it feasible to retrieve in vivo cardiac tractographies from free-breathing DTI acquisitions. The substantial improvements were observed using the WIF method instead of the previously published PCATMIP technique.
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http://dx.doi.org/10.1109/TMI.2014.2356792DOI Listing
January 2015

Detection and quantification of focal uptake in head and neck tumours: (18)F-FDG PET/MR versus PET/CT.

Eur J Nucl Med Mol Imaging 2014 Mar 10;41(3):462-75. Epub 2013 Oct 10.

Department of Imaging, Divisions of Radiology and Nuclear Medicine, Geneva University Hospital, Rue Gabrielle Perret Gentil 4, CH-1211, Geneva 14, Switzerland.

Purpose: Our objectives were to assess the quality of PET images and coregistered anatomic images obtained with PET/MR, to evaluate the detection of focal uptake and SUV, and to compare these findings with those of PET/CT in patients with head and neck tumours.

Methods: The study group comprised 32 consecutive patients with malignant head and neck tumours who underwent whole-body (18)F-FDG PET/MR and PET/CT. PET images were reconstructed using the attenuation correction sequence for PET/MR and CT for PET/CT. Two experienced observers evaluated the anonymized data. They evaluated image and fusion quality, lesion conspicuity, anatomic location, number and size of categorized (benign versus assumed malignant) lesions with focal uptake. Region of interest (ROI) analysis was performed to determine SUVs of lesions and organs for both modalities. Statistical analysis considered data clustering due to multiple lesions per patient.

Results: PET/MR coregistration and image fusion was feasible in all patients. The analysis included 66 malignant lesions (tumours, metastatic lymph nodes and distant metastases), 136 benign lesions and 470 organ ROIs. There was no statistically significant difference between PET/MR and PET/CT regarding rating scores for image quality, fusion quality, lesion conspicuity or anatomic location, number of detected lesions and number of patients with and without malignant lesions. A high correlation was observed for SUVmean and SUVmax measured on PET/MR and PET/CT for malignant lesions, benign lesions and organs (ρ = 0.787 to 0.877, p < 0.001). SUVmean and SUVmax measured on PET/MR were significantly lower than on PET/CT for malignant tumours, metastatic neck nodes, benign lesions, bone marrow, and liver (p < 0.05). The main factor affecting the difference between SUVs in malignant lesions was tumour size (p < 0.01).

Conclusion: In patients with head and neck tumours, PET/MR showed equivalent performance to PET/CT in terms of qualitative results. Comparison of SUVs revealed an excellent correlation for measurements on both modalities, but underestimation of SUVs measured on PET/MR as compared to PET/CT.
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http://dx.doi.org/10.1007/s00259-013-2580-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3913851PMC
March 2014

Assessment of cardiac motion effects on the fiber architecture of the human heart in vivo.

IEEE Trans Med Imaging 2013 Oct 19;32(10):1928-38. Epub 2013 Jun 19.

The use of diffusion tensor imaging (DTI) for studying the human heart in vivo is very challenging due to cardiac motion. This paper assesses the effects of cardiac motion on the human myocardial fiber architecture. To this end, a model for analyzing the effects of cardiac motion on signal intensity is presented. A Monte-Carlo simulation based on polarized light imaging data is then performed to calculate the diffusion signals obtained by the displacement of water molecules, which generate diffusion weighted (DW) images. Rician noise and in vivo motion data obtained from DENSE acquisition are added to the simulated cardiac DW images to produce motion-induced datasets. An algorithm based on principal components analysis filtering and temporal maximum intensity projection (PCATMIP) is used to compensate for motion-induced signal loss. Diffusion tensor parameters derived from motion-reduced DW images are compared to those derived from the original simulated DW images. Finally, to assess cardiac motion effects on in vivo fiber architecture, in vivo cardiac DTI data processed by PCATMIP are compared to those obtained from one trigger delay (TD) or one single phase acquisition. The results showed that cardiac motion produced overestimated fractional anisotropy and mean diffusivity as well as a narrower range of fiber angles. The combined use of shifted TD acquisitions and postprocessing based on image registration and PCATMIP effectively improved the quality of in vivo DW images and subsequently, the measurement accuracy of fiber architecture properties. This suggests new solutions to the problems associated with obtaining in vivo human myocardial fiber architecture properties in clinical conditions.
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http://dx.doi.org/10.1109/TMI.2013.2269195DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4704996PMC
October 2013

In vivo cardiac diffusion-weighted magnetic resonance imaging: quantification of normal perfusion and diffusion coefficients with intravoxel incoherent motion imaging.

Invest Radiol 2012 Nov;47(11):662-70

CREATIS, Université de Lyon, Lyon, France.

Objectives: Diffusion-weighted imaging (DWI) and the introduction of the intravoxel incoherent motion (IVIM) model have provided a unique method for evaluating perfusion and diffusion within a tissue without the need for a contrast agent. Despite its relevance, cardiac DWI has thus far been limited by low b values because of signal loss induced by physiological motion. The goal of this study was to develop a methodology for estimating IVIM parameters of in vivo cardiac magnetic resonance imaging using an efficient DWI acquisition framework. This was achieved by investigating various acquisition strategies (principal component analysis [PCA] filtering and temporal maximum intensity projection [PCATMIP] and single trigger delay [TD]) and fitting methods.

Material And Methods: Simulations were performed on a synthetic dataset of diffusion-weighted signal intensity (SI) to determine the fitting method that would yield IVIM parameters with the greatest accuracy. The required number of b values to correctly estimate IVIM parameters was also investigated. Breath-hold DWI scans were performed for 12 volunteers to collect several TD values during diastole. Thirteen b values ranging from 0 to 550 s/mm were used. The IVIM parameters derived using the data from all the acquired TDs (PCATMIP technique) were compared with those derived using a single acquisition performed at an optimized diastolic time point (1TD).

Results: The main result of this study was that PCATMIP, when combined with a fitting model that accounted for T1 and T2 relaxation, provided IVIM parameters with less variability. However, an acquisition performed with 1 optimized diastolic TD provided results that were as good as those provided using PCATMIP if the R-R variability during the acquisition was sufficiently low (± 5%). Furthermore, the use of only 9 b values (that could be acquired in 2 breath-holds), instead of 13 b values (requiring 3 breath-holds), was sufficient to determine the IVIM parameters.

Conclusions: This study demonstrates that IVIM is technically feasible in vivo and reports for the first time the perfusion fraction, f, and the diffusion coefficients, D and D*, for the cardiac DWI of healthy volunteers. Motion-induced signal loss, which is the main problem associated with cardiac DWI, could be avoided with the combined use of sliding acquisition during the cardiac cycle and image postprocessing with the PCATMIP algorithm. This study provides new perspectives for perfusion imaging without a contrast agent and demonstrates that IVIM parameters can act as promising tools to further characterize microvascular abnormalities or dysfunction.
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http://dx.doi.org/10.1097/RLI.0b013e31826ef901DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7453742PMC
November 2012

Sequential whole-body PET/MR scanner: concept, clinical use, and optimisation after two years in the clinic. The manufacturer's perspective.

MAGMA 2013 Feb 7;26(1):5-23. Epub 2012 Aug 7.

Philips Healthcare, Guildford Business Park, Guildford, Surrey GU2 8XH, UK.

PET and MRI are established clinical tools which provide complementary information, but clinical workflow limits widespread clinical application of both modalities in combination. The two modalities are usually situated in different hospital departments and operated and reported independently, and patients are referred for both scans, often consecutively. With the advent of PET/MR as a new hybrid imaging modality there is now a possibility of addressing these concerns. There are two different design philosophies for integrated PET/MR imaging-positioning PET inside the MRI magnet or in tandem, similar to PET/CT. The Ingenuity TF PET/MR by Philips Healthcare is a sequential PET/MR tomograph combining state-of-the-art time-of-flight PET and high-field MRI with parallel transmission capabilities. In this review article we describe the technology implemented in the system, for example RF and magnetic shielding, MR-based attenuation correction, peculiarities in scatter correction, MR system optimisation, and the philosophy behind its design. Furthermore, we provide an overview of how the system has been used during the last two years, and expectations of how the use of PET/MR may continue in the years to come. On the basis of these observations and experiences we discuss the utility of the system, clinical workflow and acquisition times, and possible ways of optimization.
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http://dx.doi.org/10.1007/s10334-012-0330-yDOI Listing
February 2013

High time-resolved cardiac functional imaging using temporal regularization for small animal on a clinical 3T scanner.

IEEE Trans Biomed Eng 2012 Apr 2;59(4):929-35. Epub 2011 Nov 2.

Division of Radiology, Faculty of Medicine, Foundation for Medical Researchers, Geneva University Hospital, University of Geneva, Geneva, Switzerland.

Accurate assessment of mice cardiac function with magnetic resonance imaging is essential for longitudinal studies and for drug development related to cardiovascular diseases. Whereas dedicated small animal MR scanners are not readily available, it would be a great advantage to be able to perform cardiac assessment on clinical systems, in particular, in the context of translational research. However, mouse imaging remains challenging since it requires both high spatial and temporal resolutions, while gradient performances of clinical scanners often limit the reachable parameters. In this study, we propose a new cine sequence, named "interleaved cine," which combines two repetitions of a standard cine sequence shifted in time in order to reach resolution parameters compatible with mice imaging. More precisely, this sequence allows temporal resolution to be reduced to 6.8 ms instead of 13.5 ms initially imposed by the system's hardware. We also propose a two-step denoising algorithm to suppress some artifacts inherent to the new interleaved cine thus allowing an efficient enhancement of the image quality. In particular, we model and suppress the periodic intensity pattern and further denoise the sequence by soft thresholding of the temporal Fourier coefficients. This sequence was successfully validated with mass and function measurements on relevant mice models of cardiovascular diseases.
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http://dx.doi.org/10.1109/TBME.2011.2174363DOI Listing
April 2012

Head-to-head comparison of eight late gadolinium-enhanced cardiac MR (LGE CMR) sequences at 1.5 tesla: from bench to bedside.

J Magn Reson Imaging 2011 Dec 3;34(6):1374-87. Epub 2011 Oct 3.

Hopital Universitaire de Genève, Genève, Switzerland.

Purpose: To compare-theoretically and experimentally-clinically available two-dimensional/three-dimensional (2D/3D), breathhold and non-breathhold, inversion-recovery (IR) gradient-echo (GRE) sequences used to differentiate between nonviable injured and normal myocardium with late gadolinium-enhanced techniques (IR-GRE2D sequence is used as a reference), and to evaluate their respective clinical benefit.

Materials And Methods: Six breathhold (2D-IR-GRE, 3D-IR-GRE, balanced steady-state free precession 2D-IR-bSSFP and 3D-IR-bSSFP, phase-sensitive 2D-PSIR-GRE, and 2D-PSIR-bSSFP) and two non-breathhold late gadolinium-enhanced techniques (single-shot 2D-ssbSSFP and 2D-PSIR-ssbSSFP) were consecutively performed in 32 coronary artery disease patients with chronic myocardial infarction. Qualitative assessment and manual planimetry were performed by two independent observers. Quantitative assessment was based on percentage signal intensity elevation between injured and normal myocardium and contrast-to-noise ratio. Theoretical simulations were compared with experimental measurements performed on phantoms with various concentrations of gadolinium.

Results: The 3D-IR-GRE image quality appeared better than the other 2D and 3D sequences, showing better delineation of complex nontransmural lesions, with significantly higher percentage signal intensity and contrast-to-noise ratio. PSIR techniques appeared more limited in differentiating sub-endocardial lesions and intracavity blood pool, but in all other cases were comparable to the other techniques. Single-shot PSIR-ssbSSFP appeared to be a valuable alternative technique when breathhold cannot be achieved.

Conclusion: We recommend 3D-IR-GRE as the method of choice for late gadolinium-enhanced cardiac magnetic resonance imaging in clinical practice.
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http://dx.doi.org/10.1002/jmri.22783DOI Listing
December 2011

Manganese kinetics demonstrated double contrast in acute but not in chronic infarction in a mouse model of myocardial occlusion reperfusion.

NMR Biomed 2012 Apr 27;25(4):489-97. Epub 2011 Jul 27.

Division of Radiology, Geneva University Hospital, University of Geneva, Faculty of Medicine, Geneva, Switzerland.

Manganese (Mn(2+)) is considered as a specific MRI contrast agent that enters viable cardiomyocytes through calcium pathways. Compared to extracellular gadolinium based contrast agents, it has the potential to assess cell viability. To date, only information from the washout phase after recirculation has been used for the detection and characterization of myocardial infarct. This study showed for the first time that in a mouse model of coronary occlusion-reperfusion, Mn(2+) wash-in kinetics are different at 24 h after surgery (acute infarction) than at eight days after surgery (chronic infarction). A fast but transient entry of Mn(2+) into the acute infarct area led to a double contrast between infarct and remote areas, whereas entry of Mn(2+) into the chronic infarct area remained reduced compared to remote regions during both wash-in and washout phases. The main hypothesis is that extracellular space is largely enhanced in acute infarction due to cell membrane rupture and interstitial edema, whereas scar tissue is densely composed of collagen fibers that reduce the distribution volume of free Mn(2+) ions. In addition to its ability to accurately depict the infarct area during the redistribution phase, Mn(2+) is also able to discriminate acute versus chronic injury by the observation of double-contrast kinetics in a mouse model of ischemia reperfusion.
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http://dx.doi.org/10.1002/nbm.1759DOI Listing
April 2012

CC chemokine CCL5 plays a central role impacting infarct size and post-infarction heart failure in mice.

Eur Heart J 2012 Aug 23;33(15):1964-74. Epub 2011 May 23.

Division of Cardiology, Foundation for Medical Researches, Department of Internal Medicine, University Hospital, Geneva, Switzerland.

Aims: The chemokine CCL5 plays a critical role as neutrophil and macrophage activator do in atherosclerosis and myocardial infarction. Thus, we investigated whether the treatment with a neutralizing monoclonal antibody (mAb) to mouse CCL5 would provide therapeutic benefit when provoking a coronary-associated ischaemic event.

Methods And Results: C57Bl/6 mice were submitted to left coronary artery permanent ligature. Then, various parameters were monitored for up to 21 days. At5 min and 3 days after coronary occlusion, mice received one intravenous injection of the rat anti-mouse CCL5 mAb or isotype IgG control. Infarct size was assessed histologically and by measuring serum cardiac troponin I levels. Kinetics of CCL5 tissue expression, leucocyte infiltration, matrix metalloproteinase (MMP) levels, and collagen deposition were histologically assessed. Serum chemokine levels were measured by enzyme-linked immunosorbent assay. Cardiac function and dimensions were assessed by magnetic resonance imaging (MRI). Chronic ischaemia increased both circulating and intracardiac levels of CCL5. At 24 h, treatment with the anti-CCL5 mAb resulted in a smaller infarct size and reduced circulating levels of chemokines. This effect was associated with reduction of neutrophil and macrophage infiltration within the infarcted myocardium. After 3 days of chronic ischaemia, anti-CCL5 mAb treatment reduced cardiac MMP-9. At 7 days, collagen content was significantly lower. At 21 days, neutralizing CCL5 improved mouse survival, cardiac myocyte size, and cardiac function.

Conclusion: Treatment with anti-CCL5 mAb significantly reduced both infarct size and post-infarction heart failure in a mouse model of chronic cardiac ischaemia. Cardioprotective effects were associated with the reduction of leucocyte recruitment within infarcted hearts.
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http://dx.doi.org/10.1093/eurheartj/ehr127DOI Listing
August 2012

Spiral demystified.

Magn Reson Imaging 2010 Jul 21;28(6):862-81. Epub 2010 Apr 21.

Radiology Clinic, Geneva University Hospital and Faculty of Medicine, University of Geneva, 1211 Geneva 14, Switzerland.

Spiral acquisition schemes offer unique advantages such as flow compensation, efficient k-space sampling and robustness against motion that make this option a viable choice among other non-Cartesian sampling schemes. For this reason, the main applications of spiral imaging lie in dynamic magnetic resonance imaging such as cardiac imaging and functional brain imaging. However, these advantages are counterbalanced by practical difficulties that render spiral imaging quite challenging. Firstly, the design of gradient waveforms and its hardware requires specific attention. Secondly, the reconstruction of such data is no longer straightforward because k-space samples are no longer aligned on a Cartesian grid. Thirdly, to take advantage of parallel imaging techniques, the common generalized autocalibrating partially parallel acquisitions (GRAPPA) or sensitivity encoding (SENSE) algorithms need to be extended. Finally, and most notably, spiral images are prone to particular artifacts such as blurring due to gradient deviations and off-resonance effects caused by B(0) inhomogeneity and concomitant gradient fields. In this article, various difficulties that spiral imaging brings along, and the solutions, which have been developed and proposed in literature, will be reviewed in detail.
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http://dx.doi.org/10.1016/j.mri.2010.03.036DOI Listing
July 2010

Myocardial infarction quantification with Manganese-Enhanced MRI (MEMRI) in mice using a 3T clinical scanner.

NMR Biomed 2010 Jun;23(5):503-13

Faculty of Medicine, University of Geneva, Geneva, Switzerland.

Manganese (Mn(2+)) was recognized early as an efficient intracellular MR contrast agent to assess cardiomyocyte viability. It had previously been used for the assessment of myocardial infarction in various animal models from pig to mouse. However, whether Manganese-Enhanced MRI (MEMRI) is also able to assess infarction in the acute phase of a coronary occlusion reperfusion model in mice has not yet been demonstrated. This model is of particular interest as it is closer to the situation encountered in the clinical setting. This study aimed to measure infarction volume taking TTC staining as a gold standard, as well as global and regional function before and after Mn(2+) injection using a clinical 3T scanner. The first step of this study was to perform a dose-response curve in order to optimize the injection protocol. Infarction volume measured with MEMRI was strongly correlated to TTC staining. Ejection fraction (EF) and percent wall thickening measurements allowed evaluation of global and regional function. While EF must be measured before Mn(2+) injection to avoid bias introduced by the reduction of contrast in cine images, percent wall thickening can be measured either before or after Mn(2+) injection and depicts accurately infarct related contraction deficit. This study is the first step for further longitudinal studies of cardiac disease in mice on a clinical 3T scanner, a widely available platform.
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http://dx.doi.org/10.1002/nbm.1489DOI Listing
June 2010
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