Publications by authors named "Thomas M Grist"

79 Publications

Deep Learning for Optimization of Abdominopelvic 4D Flow MRI Analysis.

Radiology 2021 Nov 30:212702. Epub 2021 Nov 30.

From the Departments of Radiology (A.R., T.M.G.) and Mechanical Engineering (A.R.), University of Wisconsin-Madison, 1111 Highland Ave, Madison, WI 53705.

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http://dx.doi.org/10.1148/radiol.212702DOI Listing
November 2021

Federated learning for predicting clinical outcomes in patients with COVID-19.

Nat Med 2021 10 15;27(10):1735-1743. Epub 2021 Sep 15.

Department of Internal Medicine, Yeungnam University College of Medicine, Daegu, South Korea.

Federated learning (FL) is a method used for training artificial intelligence models with data from multiple sources while maintaining data anonymity, thus removing many barriers to data sharing. Here we used data from 20 institutes across the globe to train a FL model, called EXAM (electronic medical record (EMR) chest X-ray AI model), that predicts the future oxygen requirements of symptomatic patients with COVID-19 using inputs of vital signs, laboratory data and chest X-rays. EXAM achieved an average area under the curve (AUC) >0.92 for predicting outcomes at 24 and 72 h from the time of initial presentation to the emergency room, and it provided 16% improvement in average AUC measured across all participating sites and an average increase in generalizability of 38% when compared with models trained at a single site using that site's data. For prediction of mechanical ventilation treatment or death at 24 h at the largest independent test site, EXAM achieved a sensitivity of 0.950 and specificity of 0.882. In this study, FL facilitated rapid data science collaboration without data exchange and generated a model that generalized across heterogeneous, unharmonized datasets for prediction of clinical outcomes in patients with COVID-19, setting the stage for the broader use of FL in healthcare.
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http://dx.doi.org/10.1038/s41591-021-01506-3DOI Listing
October 2021

Quantitative lung perfusion blood volume using dual energy CT-based effective atomic number (Z ) imaging.

Med Phys 2021 Nov 22;48(11):6658-6672. Epub 2021 Oct 22.

Department of Medical Physics, School of Medicine and Public Health, University of Wisconsin-Madison, Madison, Wisconsin, USA.

Background: Iodine material images (aka iodine basis images) generated from dual energy computed tomography (DECT) have been used to assess potential perfusion defects in the pulmonary parenchyma. However, iodine material images do not provide the needed absolute quantification of the pulmonary blood pool, as materials with effective atomic numbers (Z ) different from those of basis materials may also contribute to iodine material images, thus confounding the quantification of perfusion defects.

Purpose: (i) To demonstrate the limitations of iodine material images in pulmonary perfusion defect quantification and (ii) to develop and validate a new quantitative biomarker using effective atomic numbers derived from DECT images.

Methods: The quantitative relationship between the perfusion blood volume (PBV) in pulmonary parenchyma and the effective atomic number (Z ) spatial distribution was studied to show that the desired quantitative PBV maps are determined by the spatial maps of Z as , where a, b, and β are three constants. Namely, quantitative is determined by Z images instead of the iodine basis images. Perfusion maps were generated for four human subjects to demonstrate the differences between conventional iodine material image-based PBV (PBV ) derived from two-material decompositions and the proposed method.

Results: Among patients with pulmonary emboli, the proposed maps clearly show the perfusion defects while the PBV maps do not. Additionally, when there are no perfusion defects present in the derived PBV maps, no pulmonary emboli were diagnosed by an experienced thoracic radiologist.

Conclusion: Effective atomic number-based quantitative PBV maps provide the needed sensitive and specific biomarker to quantify pulmonary perfusion defects.
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http://dx.doi.org/10.1002/mp.15227DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8595877PMC
November 2021

Myocarditis Associated with mRNA COVID-19 Vaccination.

Radiology 2021 11 20;301(2):E409-E411. Epub 2021 Jul 20.

From the Departments of Radiology (J.S., D.A.B., W.S.B., T.M.G., M.L.S., S.B.R.), Medical Physics (D.A.B., T.M.G., S.B.R.), Medicine (W.S.B., S.B.R.), Biomedical Engineering (T.M.G., S.B.R.), and Emergency Medicine (S.B.R.), University of Wisconsin-Madison School of Medicine and Public Health, 600 Highland Ave, Madison, WI 53792.

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http://dx.doi.org/10.1148/radiol.2021211430DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8574056PMC
November 2021

Evaluation for Myocarditis in Competitive Student Athletes Recovering From Coronavirus Disease 2019 With Cardiac Magnetic Resonance Imaging.

JAMA Cardiol 2021 08;6(8):945-950

Department of Radiology, University of Wisconsin, Madison.

Importance: The utility of cardiac magnetic resonance imaging (MRI) as a screening tool for myocarditis in competitive student athletes returning to training after recovering from coronavirus disease 2019 (COVID-19) infection is unknown.

Objective: To describe the prevalence and severity of cardiac MRI findings of myocarditis in a population of competitive student athletes recovering from COVID-19.

Design, Setting, And Participants: In this case series, an electronic health record search was performed at our institution (University of Wisconsin) to identify all competitive athletes (a consecutive sample) recovering from COVID-19, who underwent gadolinium-enhanced cardiac MRI between January 1, 2020, and November 29, 2020. The MRI findings were reviewed by 2 radiologists experienced in cardiac imaging, using the updated Lake Louise criteria. Serum markers of myocardial injury and inflammation (troponin-I, B-type natriuretic peptide, C-reactive protein, and erythrocyte sedimentation rate), an electrocardiogram, transthoracic echocardiography, and relevant clinical data were obtained.

Exposures: COVID-19 infection, confirmed using reverse transcription-polymerase chain reaction testing.

Main Outcomes And Measures: Prevalence and severity of MRI findings consistent with myocarditis among young competitive athletes recovering from COVID-19.

Results: A total of 145 competitive student athletes (108 male and 37 female individuals; mean age, 20 years; range, 17-23 years) recovering from COVID-19 were included. Most patients had mild (71 [49.0%]) or moderate (40 [27.6%]) symptoms during the acute infection or were asymptomatic (24 [16.6%]). Symptoms were not specified or documented in 10 patients (6.9%). No patients required hospitalization. Cardiac MRIs were performed a median of 15 days (range, 11-194 days) after patients tested positive for COVID-19. Two patients had MRI findings consistent with myocarditis (1.4% [95% CI, 0.4%-4.9%]). Of these, 1 patient had marked nonischemic late gadolinium enhancement and T2-weighted signal abnormalities over multiple segments, along with an abnormal serum troponin-I level; the second patient had 1-cm nonischemic mild late gadolinium enhancement and mild T2-weighted signal abnormalities, with normal laboratory values.

Conclusions And Relevance: In this case series study, based on MRI findings, there was a low prevalence of myocarditis (1.4%) among student athletes recovering from COVID-19 with no or mild to moderate symptoms. Thus, the utility of cardiac MRI as a screening tool for myocarditis in this patient population is questionable.
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http://dx.doi.org/10.1001/jamacardio.2020.7444DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7809616PMC
August 2021

The Next Chapter in MRI: Back to the Future?

Authors:
Thomas M Grist

Radiology 2019 11 1;293(2):394-395. Epub 2019 Oct 1.

From the Department of Radiology, University of Wisconsin-Madison, School of Medicine and Public Health, 600 Highland Ave, Madison, WI 53705.

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http://dx.doi.org/10.1148/radiol.2019192011DOI Listing
November 2019

Why physics in medicine?

Phys Med 2019 Aug;64:319-322

Department of Radiology, School of Medicine and Public Health, University of Wisconsin, Madison, WI, USA.

Despite its crucial role in the development of new medical imaging technologies, in clinical practice, physics has primarily been involved in technical evaluation of technologies. However, this narrow role is no longer adequate. New trajectories in medicine call for a stronger role for physics in the clinic. The movement towards evidence-based, quantitative, and value-based medicine requires physicists to play a more integral role in delivering innovative precision care through the intentional clinical application of physical sciences. There are three aspects of this clinical role: technology assessment based on metrics as they relate to expected clinical performance, optimized use of technologies for patient-centered clinical outcomes, and retrospective analysis of imaging operations to ensure attainment of expectations in terms of quality and variability. These tasks fuel the drive towards high-quality, consistent practice of medical imaging that is patient-centered, evidence-based, and safe. While this particular article focuses on imaging, this trajectory and paradigm is equally applicable to the multitudes of the applications of physics in medicine.
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http://dx.doi.org/10.1016/j.ejmp.2019.04.027DOI Listing
August 2019

Society of Chairs of Academic Radiology Departments Statement of Support for Paid Parental Leave.

J Am Coll Radiol 2019 03;16(3):271-272

The Louis Marx Professor and Chair, Department of Radiology, NYU Langone Health, New York, New York.

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http://dx.doi.org/10.1016/j.jacr.2018.12.029DOI Listing
March 2019

Why Physics in Medicine?

J Am Coll Radiol 2018 07 18;15(7):1008-1012. Epub 2018 May 18.

Department of Radiology, School of Medicine and Public Health, University of Wisconsin, Madison, Wisconsin.

Despite its crucial role in the development of new medical imaging technologies, in clinical practice, physics has primarily been involved in the technical evaluation of technologies. However, this narrow role is no longer adequate. New trajectories in medicine call for a stronger role for physics in the clinic. The movement toward evidence-based, quantitative, and value-based medicine requires physicists to play a more integral role in delivering innovative precision care through the intentional clinical application of physical sciences. There are three aspects of this clinical role: technology assessment based on metrics as they relate to expected clinical performance, optimized use of technologies for patient-centered clinical outcomes, and retrospective analysis of imaging operations to ensure attainment of expectations in terms of quality and variability. These tasks fuel the drive toward high-quality, consistent practice of medical imaging that is patient centered, evidence based, and safe. While this particular article focuses on imaging, this trajectory and paradigm is equally applicable to the multitudes of the applications of physics in medicine.
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http://dx.doi.org/10.1016/j.jacr.2018.03.043DOI Listing
July 2018

Clinical outcomes after magnetic resonance angiography (MRA) versus computed tomographic angiography (CTA) for pulmonary embolism evaluation.

Emerg Radiol 2018 Oct 10;25(5):469-477. Epub 2018 May 10.

Department of Radiology, University of Wisconsin, Madison, WI, USA.

Purpose: To compare patient outcomes following magnetic resonance angiography (MRA) versus computed tomographic angiography (CTA) ordered for suspected pulmonary embolism (PE).

Methods: In this IRB-approved, single-center, retrospective, case-control study, we reviewed the medical records of all patients evaluated for PE with MRA during a 5-year period along with age- and sex-matched controls evaluated with CTA. Only the first instance of PE evaluation during the study period was included. After application of our exclusion criteria to both study arms, the analysis included 1173 subjects. The primary endpoint was major adverse PE-related event (MAPE), which we defined as major bleeding, venous thromboembolism, or death during the 6 months following the index imaging test (MRA or CTA), obtained through medical record review. Logistic regression, chi-square test for independence, and Fisher's exact test were used with a p < 0.05 threshold.

Results: The overall 6-month MAPE rate following MRA (5.4%) was lower than following CTA (13.6%, p < 0.01). Amongst outpatients, the MAPE rate was lower for MRA (3.7%) than for CTA (8.0%, p = 0.01). Accounting for age, sex, referral source, BMI, and Wells' score, patients were less likely to suffer MAPE than those who underwent CTA, with an odds ratio of 0.44 [0.24, 0.80]. Technical success rate did not differ significantly between MRA (92.6%) and CTA (90.5%) groups (p = 0.41).

Conclusion: Within the inherent limitations of a retrospective case-controlled analysis, we observed that the rate of MAPE was lower (more favorable) for patients following pulmonary MRA for the primary evaluation of suspected PE than following CTA.
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http://dx.doi.org/10.1007/s10140-018-1609-8DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6119517PMC
October 2018

Contrast-enhanced pulmonary MRA for the primary diagnosis of pulmonary embolism: current state of the art and future directions.

Br J Radiol 2017 Jun 12;90(1074):20160901. Epub 2017 Apr 12.

1 Department of Radiology, University of Wisconsin-Madison, Madison, WI, USA.

CT pulmonary angiography (CTPA) is currently considered the imaging standard of care for the diagnosis of pulmonary embolism (PE). Recent advances in contrast-enhanced pulmonary MR angiography (MRA) techniques have led to increased use of this modality for the detection of PE in the proper clinical setting. This review is intended to provide an introduction to the state-of-the-art techniques used in pulmonary MRA for the detection of PE and to discuss possible future directions for this modality. This review discusses the following issues pertinent to MRA for the diagnosis of PE: (1) the diagnostic efficacy and clinical effectiveness for pulmonary MRA relative to CTPA, (2) the different pulmonary MRA techniques used for the detection of PE, (3) guidance for building a clinical service at their institution using MRA and (4) future directions of PE MRA. Our principal aim was to show how pulmonary MRA can be used as a safe, effective modality for the diagnosis of clinically significant PE, particularly for those patients where there are concerns about ionizing radiation or contraindications/allergies to the iodinated contrast material.
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http://dx.doi.org/10.1259/bjr.20160901DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5602179PMC
June 2017

Bits and bytes: the future of radiology lies in informatics and information technology.

Eur Radiol 2017 Sep 9;27(9):3647-3651. Epub 2017 Mar 9.

Department of Radiological Sciences, UCLA Medical Center, 924 Westwood Blvd., Ste. 805, Los Angeles, CA, 90095, USA.

Advances in informatics and information technology are sure to alter the practice of medical imaging and image-guided therapies substantially over the next decade. Each element of the imaging continuum will be affected by substantial increases in computing capacity coincident with the seamless integration of digital technology into our society at large. This article focuses primarily on areas where this IT transformation is likely to have a profound effect on the practice of radiology.

Key Points: • Clinical decision support ensures consistent and appropriate resource utilization. • Big data enables correlation of health information across multiple domains. • Data mining advances the quality of medical decision-making. • Business analytics allow radiologists to maximize the benefits of imaging resources.
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http://dx.doi.org/10.1007/s00330-016-4688-5DOI Listing
September 2017

Incidence of actionable findings on contrast enhanced magnetic resonance angiography ordered for pulmonary embolism evaluation.

Eur J Radiol 2016 Aug 19;85(8):1383-9. Epub 2016 May 19.

Department of Radiology, University of Wisconsin School of Medicine and Public Health, Madison, WI, United States; Department of Medical Physics, University of Wisconsin School of Medicine and Public Health, Madison, WI, United States; Department of Pediatrics, University of Wisconsin School of Medicine and Public Health, Madison, WI, United States.

Purpose: To determine the incidence of actionable findings on contrast-enhanced magnetic resonance angiography (MRA) scans performed for the primary diagnosis of pulmonary embolism (PE).

Materials And Methods: This was a HIPAA-compliant and IRB-approved single center, retrospective study of consecutive series of patients evaluated with contrast-enhanced MRA for PE. The final radiology report of each MRA was reviewed. All technically adequate negative exams were included in the analysis. The findings were divided into three types: those requiring further action (actionable-Type 1) those not requiring follow-up (non-actionable-Type 2) and normal exams. We compared our results with the literature regarding the use of computed tomographic angiography (CTA) in this scenario using Fisher's exact test.

Results: 580 MRA scans for PE were performed. There were 561/580 (97%) technically adequate exams. Of these, 514/580 (89%) were negative and 47/580 (8%) were positive for PE. In the PE negative group of 514 exams, Type 1 findings were identified in 85/514 (17%), 188/514 (36%) cases were Type 2 and 241/514 (47.0%) were Type 3. There was no significant difference between the incidence of Type 1 and the combination of Type 2 and Type 3 findings on MRA and the reported incidence of actionable findings derived from CTA negative exams for PE (p<0.5).

Conclusion: MRA as a first-line test for PE can identify actionable findings in those patients without PE, with an incidence similar to that reported in the literature for CTA.
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http://dx.doi.org/10.1016/j.ejrad.2016.05.008DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7304888PMC
August 2016

Contrast enhanced pulmonary magnetic resonance angiography for pulmonary embolism: Building a successful program.

Eur J Radiol 2016 Mar 29;85(3):553-63. Epub 2015 Dec 29.

Department of Radiology, University of Wisconsin-Madison, Madison, WI, United States; Department of Medical Physics, University of Wisconsin-Madison, Madison, WI, United States; Department of Emergency Medicine, University of Wisconsin-Madison, Madison, WI, United States; Department of Medicine, University of Wisconsin-Madison, Madison, WI, United States; Department of Biomedical Engineering, University of Wisconsin-Madison, Madison, WI, United States.

The performance of contrast enhanced pulmonary magnetic resonance angiography (MRA) for the diagnosis of pulmonary embolism (PE) is an effective non-ionizing alternative to contrast enhanced computed tomography and nuclear medicine ventilation/perfusion scanning. However, the technical success of these exams is very dependent on careful attention to the details of the MRA acquisition protocol and requires reader familiarity with MRI and its artifacts. Most practicing radiologists are very comfortable with the performance and interpretation of computed tomographic angiography (CTA) performed to detect pulmonary embolism but not all are as comfortable with the use of MRA in this setting. The purpose of this review is to provide the general radiologist with the tools necessary to build a successful pulmonary embolism MRA program. This review will cover in detail image acquisition, image interpretation, and some key elements of outreach that help to frame the role of MRA to consulting clinicians and hospital administrators. It is our aim that this resource will help build successful clinical pulmonary embolism MRA programs that are well received by patients and physicians, reduce the burden of medical imaging radiation, and maintain good patient outcomes.
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http://dx.doi.org/10.1016/j.ejrad.2015.12.018DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4751592PMC
March 2016

25 Years of Contrast-Enhanced MRI: Developments, Current Challenges and Future Perspectives.

Adv Ther 2016 Jan 25;33(1):1-28. Epub 2016 Jan 25.

MR and CT Contrast Media Research, Bayer HealthCare, Berlin, Germany.

Unlabelled: In 1988, the first contrast agent specifically designed for magnetic resonance imaging (MRI), gadopentetate dimeglumine (Magnevist(®)), became available for clinical use. Since then, a plethora of studies have investigated the potential of MRI contrast agents for diagnostic imaging across the body, including the central nervous system, heart and circulation, breast, lungs, the gastrointestinal, genitourinary, musculoskeletal and lymphatic systems, and even the skin. Today, after 25 years of contrast-enhanced (CE-) MRI in clinical practice, the utility of this diagnostic imaging modality has expanded beyond initial expectations to become an essential tool for disease diagnosis and management worldwide. CE-MRI continues to evolve, with new techniques, advanced technologies, and novel contrast agents bringing exciting opportunities for more sensitive, targeted imaging and improved patient management, along with associated clinical challenges. This review aims to provide an overview on the history of MRI and contrast media development, to highlight certain key advances in the clinical development of CE-MRI, to outline current technical trends and clinical challenges, and to suggest some important future perspectives.

Funding: Bayer HealthCare.
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http://dx.doi.org/10.1007/s12325-015-0275-4DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4735235PMC
January 2016

Longitudinal Assessment of Renal Perfusion and Oxygenation in Transplant Donor-Recipient Pairs Using Arterial Spin Labeling and Blood Oxygen Level-Dependent Magnetic Resonance Imaging.

Invest Radiol 2016 Feb;51(2):113-20

From the Departments of *Medical Physics, †Medicine, ‡Surgery, §Radiology, ∥Obstetrics and Gynecology, and ¶Biomedical Engineering, University of Wisconsin, Madison, WI.

Objectives: The aims of this study were to assess renal function in kidney transplant recipients and their respective donors over 2 years using arterial spin labeling (ASL) and blood oxygen level-dependent (BOLD) magnetic resonance imaging (MRI) and to prospectively evaluate the effect of losartan on functional MRI measures in recipients.

Materials And Methods: The study included 15 matched pairs of renal transplant donors and recipients. Arterial spin labeling and BOLD MRI of the kidneys were performed on donors before transplant surgery (baseline) and on both donors and recipients at 3 months, 1 year, and 2 years after transplant. After 3 months, 7 of the 15 recipients were prescribed 25 to 50 mg/d losartan for the remainder of the study. A linear mixed-effects model was used to evaluate perfusion, R2*, estimated glomerular filtration rate, and fractional excretion of sodium for changes across time or associated with losartan treatment.

Results: In donors, cortical perfusion in the remaining kidney decreased by 50 ± 19 mL/min per 100 g (11.8%) between baseline and 2 years (P < 0.05), while cortical R2* declined modestly by 0.7 ± 0.3 s-1 (5.6%; P < 0.05). In transplanted kidneys, cortical perfusion decreased markedly by 141 ± 21 mL/min per 100 g (34.2%) between baseline and 2 years (P < 0.001), while medullary R2* declined by 1.5 ± 0.8 s-1 (8.3%; P = 0.06). Single-kidney estimated glomerular filtration rate increased between baseline and 2 years by 17.7 ± 2.7 mL/min per 1.73 m (40.3%; P < 0.0001) in donors and to 14.6 ± 4.3 mL/min per 1.73 m (33.3%; P < 0.01) in recipients. Cortical perfusion at 1 and 2 years in recipients receiving 25 to 50 mg/d losartan was 62 ± 24 mL/min per 100 g higher than recipients not receiving the drug (P < 0.05). No significant effects of losartan were observed for any other markers of renal function.

Conclusions: The results suggest an important role for noninvasive functional monitoring with ASL and BOLD MRI in kidney transplant recipients and donors, and they indicate a potentially beneficial effect of losartan in recipients.
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http://dx.doi.org/10.1097/RLI.0000000000000210DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4697870PMC
February 2016

Comparison of models and contrast agents for improved signal and signal linearity in dynamic contrast-enhanced pulmonary magnetic resonance imaging.

Invest Radiol 2015 Mar;50(3):174-8

From the *Department of Medical Physics, University of Wisconsin; †Global MR Applications and Workflow, GE Healthcare; Departments of ‡Radiology, §Biomedical Engineering, and ∥Pediatrics, University of Wisconsin, Madison, WI.

Objectives: The objectives of this study were to compare pulmonary blood flow (PBF) measurements acquired with 3 previously published models (low-dose "single bolus," "dual bolus" and a "nonlinear correction" algorithm) for addressing the nonlinear relationship between contrast agent concentration and magnetic resonance signal in the arterial input function (AIF) and to compare both lung signal and PBF measurements obtained using gadopentetate dimeglumine (Gd-DTPA, Magnevist) with those obtained using the high-relaxivity agent gadobenate dimeglumine (Gd-BOPTA, Multihance).

Materials And Methods: Ten of 12 healthy humans were successfully scanned on 2 consecutive days at 1.5 T. Contrast-enhanced pulmonary perfusion scans were acquired with a 3-dimensional spoiled gradient echo pulse sequence and interleaved variable density k-space sampling with a 1-second frame rate and 4 × 4 × 4-mm resolution. Each day, 2 perfusion scans were acquired with either Gd-DTPA or Gd-BOPTA; the order of the administered contrast agent was randomized. Region of interest analysis was used to determine PBF on the basis of the indicator dilution theory. Linear mixed-effects modeling was used to compare the AIF models and contrast agents.

Results: With Gd-DTPA, no significant differences were observed between the mean PBF calculated for the single bolus (323 ± 110 mL/100mL/min), dual bolus (315 ± 177 mL/100mL/min), and nonlinear correction (298 ± 100 mL/100mL/min) approach. With Gd-BOPTA, the mean PBF using the dual bolus approach (245 ± 103 mL/100mL/min) was lower than with the single bolus (345 ± 130 mL/100mL/min P < 0.01) and nonlinear correction (321 ± 115 mL/100mL/min; P = 0.02). Peak lung enhancement was significantly higher in all regions with Gd-BOPTA than with Gd-DTPA (P << 0.01).

Conclusions: The dual bolus approach with Gd-BOPTA resulted in a significantly lower PBF than did the other combinations of contrast agent and AIF model. No other statistically significant differences were found. Given the much higher signal in the lung parenchyma using Gd-BOPTA, the use of Gd-BOPTA with either single bolus or the nonlinear correction method appears most promising for voxelwise perfusion quantification using 3-dimensional dynamic contrast-enhanced pulmonary perfusion magnetic resonance imaging.
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http://dx.doi.org/10.1097/RLI.0000000000000122DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4318764PMC
March 2015

Measurements of wall shear stress and aortic pulse wave velocity in swine with familial hypercholesterolemia.

J Magn Reson Imaging 2015 May 25;41(5):1475-85. Epub 2014 Jun 25.

Department of Medical Physics, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, USA; Department of Radiology, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, USA.

Purpose: To assess measurements of pulse wave velocity (PWV) and wall shear stress (WSS) in a swine model of atherosclerosis.

Materials And Methods: Nine familial hypercholesterolemic (FH) swine with angioplasty balloon catheter-induced atherosclerotic lesions to the abdominal aorta (injured group) and 10 uninjured FH swine were evaluated with a 4D phase contrast (PC) magnetic resonance imaging (MRI) acquisition, as well as with radial and Cartesian 2D PC acquisitions, on a 3T MR scanner. PWV values were computed from the 2D and 4D PC techniques, compared between the injured and uninjured swine, and validated against reference standard pressure probe-based PWV measurements. WSS values were also computed from the 4D PC MRI technique and compared between injured and uninjured groups.

Results: PWV values were significantly greater in the injured than in the uninjured groups with the 4D PC MRI technique (P = 0.03) and pressure probes (P = 0.02). No significant differences were found in PWV between groups using the 2D PC techniques (P = 0.75-0.83). No significant differences were found for WSS values between the injured and uninjured groups.

Conclusion: The 4D PC MRI technique provides a promising means of evaluating PWV and WSS in a swine model of atherosclerosis, providing a potential platform for developing the technique for the early detection of atherosclerosis.
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http://dx.doi.org/10.1002/jmri.24681DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4276731PMC
May 2015

Review of MRI-based measurements of pulse wave velocity: a biomarker of arterial stiffness.

Cardiovasc Diagn Ther 2014 Apr;4(2):193-206

1 Department of Medical Physics, 2 Department of Radiology, University of Wisconsin School of Medicine and Public Health,1111 Highland Avenue, Madison, WI 53705-2275, USA.

Atherosclerosis is the leading cause of cardiovascular disease (CVD) in the Western world. In the early development of atherosclerosis, vessel walls remodel outwardly such that the vessel luminal diameter is minimally affected by early plaque development. Only in the late stages of the disease does the vessel lumen begin to narrow-leading to stenoses. As a result, angiographic techniques are not useful for diagnosing early atherosclerosis. Given the absence of stenoses in the early stages of atherosclerosis, CVD remains subclinical for decades. Thus, methods of diagnosing atherosclerosis early in the disease process are needed so that affected patients can receive the necessary interventions to prevent further disease progression. Pulse wave velocity (PWV) is a biomarker directly related to vessel stiffness that has the potential to provide information on early atherosclerotic disease burden. A number of clinical methods are available for evaluating global PWV, including applanation tonometry and ultrasound. However, these methods only provide a gross global measurement of PWV-from the carotid to femoral arteries-and may mitigate regional stiffness within the vasculature. Additionally, the distance measurements used in the PWV calculation with these methods can be highly inaccurate. Faster and more robust magnetic resonance imaging (MRI) sequences have facilitated increased interest in MRI-based PWV measurements. This review provides an overview of the state-of-the-art in MRI-based PWV measurements. In addition, both gold standard and clinical standard methods of computing PWV are discussed.
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http://dx.doi.org/10.3978/j.issn.2223-3652.2014.03.04DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3996237PMC
April 2014

Whole-heart chemical shift encoded water-fat MRI.

Magn Reson Med 2014 Sep 1;72(3):718-25. Epub 2013 Nov 1.

Department of Radiology, University of Wisconsin, Madison, Wisconsin, USA.

Purpose: To develop and evaluate a free-breathing chemical-shift-encoded (CSE) spoiled gradient-recalled echo (SPGR) technique for whole-heart water-fat imaging at 3 Tesla (T).

Methods: We developed a three-dimensional (3D) multi-echo SPGR pulse sequence with electrocardiographic gating and navigator echoes and evaluated its performance at 3T in healthy volunteers (N = 6) and patients (N = 20). CSE-SPGR, 3D SPGR, and 3D balanced-SSFP with chemical fat saturation were compared in six healthy subjects with images evaluated for overall image quality, level of residual artifacts, and quality of fat suppression. A similar scoring system was used for the patient datasets.

Results: Images of diagnostic quality were acquired in all but one subject. CSE-SPGR performed similarly to SPGR with fat saturation, although it provided a more uniform fat suppression over the whole field of view. Balanced-SSFP performed worse than SPGR-based methods. In patients, CSE-SPGR produced excellent fat suppression near metal. Overall image quality was either good (7/20) or excellent (12/20) in all but one patient. There were significant artifacts in 5/20 clinical cases.

Conclusion: CSE-SPGR is a promising technique for whole-heart water-fat imaging during free-breathing. The robust fat suppression in the water-only image could improve assessment of complex morphology at 3T and in the presence of off-resonance, with additional information contained in the fat-only image.
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http://dx.doi.org/10.1002/mrm.24982DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4007374PMC
September 2014

Effectiveness of MR angiography for the primary diagnosis of acute pulmonary embolism: clinical outcomes at 3 months and 1 year.

J Magn Reson Imaging 2013 Oct 1;38(4):914-25. Epub 2013 Apr 1.

Department of Radiology, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, USA.

Purpose: To determine the effectiveness of MR angiography for pulmonary embolism (MRA-PE) in symptomatic patients.

Materials And Methods: We retrospectively reviewed all patients whom were evaluated for possible pulmonary embolism (PE) using MRA-PE. A 3-month and 1-year from MRA-PE electronic medical record (EMR) review was performed. Evidence for venous thromboembolism (VTE) (or death from PE) within the year of follow-up was the outcome surrogate for this study.

Results: There were 190 MRA-PE exams performed with 97.4% (185/190) of diagnostic quality. There were 148 patients (120 F: 28 M) that had both a diagnostic MRA-PE exam and 1 complete year of EMR follow-up. There were 167 patients (137 F: 30 M) with 3 months or greater follow-up. We found 83% (139/167) and 81% (120/148) MRA-PE exams negative for PE at 3 months and 1 year, respectively. Positive exams for PE were seen in 14% (23/167). During the 1-year follow-up period, five patients (false negative) were diagnosed with DVT (5/148 = 3.4 %), and one of these patients also experienced a non-life-threatening PE. The negative predictive value (NPV) for MRA-PE was 97% (92-99; 95% CI) at 3 months and 96% (90-98; 95% CI) with 1 year of follow-up.

Conclusion: The NPV of MRA-PE, when used for the primary diagnosis of pulmonary embolism in symptomatic patients, were found to be similar to the published values for CTA-PE. In addition, the technical success rate and safety of MRA-PE were excellent.
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http://dx.doi.org/10.1002/jmri.24057DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3970266PMC
October 2013

Repeatability and internal consistency of abdominal 2D and 4D phase contrast MR flow measurements.

Acad Radiol 2013 Jun 16;20(6):699-704. Epub 2013 Mar 16.

Department of Medical Physics, University of Wisconsin School of Medicine and Public Health, 1111 Highland Avenue, Madison, WI, USA 53705-2275, USA.

Rationale And Objectives: The aim of this study was to assess the repeatability and internal consistency of flow measurements in the renal arteries and pararenal aorta with the use of standard two-dimensional (2D) and novel four-dimensional (4D) phase contrast (PC) magnetic resonance imaging (MRI).

Materials And Methods: Ten healthy volunteers were imaged with a radially undersampled 4D PC technique centered over the renal arteries and with four 2D PC slices placed in the supra/infrarenal aorta and the left/right renal arteries; this MRI exam was performed twice on each subject. Flow measurements in all four vessels were computed from 2D and 4D PC data sets. Student's t-tests (P < .05) were used to assess differences between in-flow (suprarenal aorta) and out-flow (infrarenal aorta + left renal artery + right renal artery) for the 2D and 4D techniques, to compare in- and out-flow, and to compare repeated measurements of 2D and 4D flow measurements.

Results: No significant differences were found in repeated measurements of 2D (P = .15) or 4D (P = .39) data. No significant difference was found between 2D (3.4 ± 2.8 mL/cardiac cycle) and 4D (3.5 ± 2.7 mL/cardiac cycle) in- and out-flow differences (P = .88). Out-flow was greater than in-flow for 2D measurements (P = .003); no difference was found for 4D measurements.

Conclusion: The 2D and 4D techniques demonstrated strong repeatability and internal consistency of flow measurements in the renal arteries and pararenal aorta.
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http://dx.doi.org/10.1016/j.acra.2012.12.019DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3897393PMC
June 2013

Dynamic and static magnetic resonance angiography of the supra-aortic vessels at 3.0 T: intraindividual comparison of gadobutrol, gadobenate dimeglumine, and gadoterate meglumine at equimolar dose.

Invest Radiol 2013 Mar;48(3):121-8

Institute for Clinical Radiology, Ludwig Maximilians University Hospital Munich, Munich, Germany.

Purpose: The purpose of this study was the intraindividual comparison of a 1.0 M and two 0.5 M gadolinium-based contrast agents (GBCA) using equimolar dosing in dynamic and static magnetic resonance angiography (MRA) of the supra-aortic vessels.

Materials And Methods: In this institutional review board-approved study, a total of 20 healthy volunteers (mean ± SD age, 29 ± 6 years) underwent 3 consecutive supra-aortic MRA examinations on a 3.0 T magnetic resonance system. The order of GBCA (Gadobutrol, Gadobenate dimeglumine, and Gadoterate meglumine) was randomized with a minimum interval of 48 hours between the examinations. Before each examination and 45 minutes after each examination, circulatory parameters were recorded. Total GBCA dose per MRA examination was 0.1 mmol/kg with a 0.03 mmol/kg and 0.07 mmol/kg split for dynamic and static MRA, respectively, injected at a rate of 2 mL/s. Two blinded readers qualitatively assessed static MRA data sets independently using pairwise rankings (superior, inferior, and equal). In addition, quantitative analysis was performed with signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) evaluation as well as vessel sharpness analysis of static MRA using an in-house-developed semiautomated tool. Dynamic MRA was evaluated for maximal SNR. Statistical analysis was performed using the Cohen κ, the Wilcoxon rank sum tests, and mixed effects models.

Results: No significant differences of hemodynamic parameters were observed. In static MRA, Gadobutrol was rated superior to Gadoterate meglumine (P < 0.05) and equal to Gadobenate dimeglumine (P = 0.06) with good to excellent reader agreement (κ, 0.66-0.83). In static MRA, SNR was significantly higher using 1.0 M Gadobutrol as compared with either 0.5 M agent (P < 0.05 and P < 0.05) and CNR was significantly higher as compared with Gadoterate meglumine (P < 0.05), whereas CNR values of Gadobutrol data sets were not significantly different as compared with Gadobenate dimeglumine (P = 0.13). Differences in CNR between Gadobenate dimeglumine and Gadoterate meglumine were not significant (P = 0.78). Differences in vessel sharpness between the different GBCAs were also not significant (P > 0.05). Maximal SNR in dynamic MRA using Gadobutrol was significantly higher than both comparators at the level of the proximal and distal internal carotid artery (P < 0.05 and P < 0.05; P < 0.05 and P < 0.05).

Conclusions: At equimolar doses, 1.0 M Gadobutrol demonstrates higher SNR/CNR than do Gadobenate dimeglumine and Gadoterate meglumine, with superior image quality as compared with Gadoterate meglumine for dynamic and static carotid MRA. Despite the shortened bolus with Gadobutrol, no blurring of vessel edges was observed.
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http://dx.doi.org/10.1097/RLI.0b013e31827752b4DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3818529PMC
March 2013

Aortic pulse wave velocity measurements with undersampled 4D flow-sensitive MRI: comparison with 2D and algorithm determination.

J Magn Reson Imaging 2013 Apr 2;37(4):853-9. Epub 2012 Nov 2.

Department of Medical Physics, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin 53705-2275, USA.

Purpose: To compare pulse wave velocity (PWV) measurements obtained from radially undersampled 4D phase-contrast magnetic resonance imaging (PC-MRI) with 2D PC measurements and to evaluate four PWV algorithms.

Materials And Methods: PWV was computed from radially undersampled 3D, 3-directionally velocity-encoded PC-MRI (4D) acquisitions performed on a 3T MR scanner in 18 volunteers. High temporal resolution 2D PC scans serving as a reference standard were available in 14 volunteers. Four PWV algorithms were tested: time-to-upstroke (TTU), time-to-peak (TTP), time-to-foot (TTF), and cross-correlation (XCorr). Bland-Altman analysis was used to determine inter- and intraobserver reproducibility and to compare differences between algorithms. Differences in age and PWV measurements were analyzed with Student's t-tests. The variability of age-corrected data was assessed with a Brown-Forsythe analysis of variance (ANOVA) test.

Results: 2D (4.6-5.3 m/s) and 4D (3.8-4.8 m/s) PWV results were in agreement with previously reported values in healthy subjects. Of the four PWV algorithms, the TTU, TTF, and XCorr algorithms gave similar and reliable results. Average biases of +0.30 m/s and -0.01 m/s were determined for intra- and interobserver variability, respectively. The Brown-Forsythe test revealed that no differences in variability could be found between 2D and 4D PWV measurements.

Conclusion: 4D PC-MRI with radial undersampling provides reliable and reproducible measurements of PWV. TTU, TTF, and XCorr were the preferred PWV algorithms.
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http://dx.doi.org/10.1002/jmri.23877DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3566322PMC
April 2013

Peripheral MR Angiography.

Magn Reson Imaging Clin N Am 2012 Nov 25;20(4):761-76. Epub 2012 Sep 25.

Department of Radiology, University of Wisconsin-Madison, Madison, WI 53792-3252, USA.

Since the introduction of contrast-enhanced MR angiography (MRA), several different techniques for imaging the peripheral arteries have evolved. All of them provide good diagnostic image quality, whereas some older techniques suffer from drawbacks, such as long acquisition time, impaired image quality from venous enhancement, and limited spatial resolution. MRA provides the most comprehensive modality offering the ability to tailor the examination to the patient and the specific question to be answered. The drawbacks experienced at the introduction of MRA to clinical routine have largely been overcome or at least diminished, so that the benefits of MRA outbalance the limitations.
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http://dx.doi.org/10.1016/j.mric.2012.08.002DOI Listing
November 2012

Time-resolved angiography: Past, present, and future.

J Magn Reson Imaging 2012 Dec 7;36(6):1273-86. Epub 2012 May 7.

Department of Radiology, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, USA.

The introduction of digital subtraction angiography (DSA) in 1980 provided a method for real time 2D subtraction imaging. Later, 4D magnetic resonance (MR) angiography emerged beginning with techniques like Keyhole and time-resolved imaging of contrast kinetics (TRICKS) that provided frame rates of one every 5 seconds with limited spatial resolution. Undersampled radial acquisition was subsequently developed. The 3D vastly undersampled isotropic projection (VIPR) technique allowed undersampling factors of 30-40. Its combination with phase contrast displays time-resolved flow dynamics within the cardiac cycle and has enabled the measurement of pressure gradients in small vessels. Meanwhile similar accelerations were achieved using Cartesian acquisition with projection reconstruction (CAPR), a Cartesian acquisition with 2D parallel imaging. Further acceleration is provided by constrained reconstruction techniques such as highly constrained back-projection reconstruction (HYPR) and its derivatives, which permit acceleration factors approaching 1000. Hybrid MRA combines a separate phase contrast, time-of flight, or contrast-enhanced acquisition to constrain the reconstruction of contrast-enhanced time frames providing exceptional spatial and temporal resolution and signal-to-noise ratio (SNR). This can be extended to x-ray imaging where a 3D DSA examination can be used to constrain the reconstruction of time-resolved 3D volumes. Each 4D DSA (time-resolved 3D DSA) frame provides spatial resolution and SNR comparable to 3D DSA, thus removing a major limitation of intravenous DSA. Similar techniques have provided the ability to do 4D fluoroscopy.
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http://dx.doi.org/10.1002/jmri.23646DOI Listing
December 2012

Noninvasive assessment of transstenotic pressure gradients in porcine renal artery stenoses by using vastly undersampled phase-contrast MR angiography.

Radiology 2011 Oct 3;261(1):266-73. Epub 2011 Aug 3.

Department of Radiology, University of Wisconsin School of Medicine and Public Health, Madison, WI 53705-2275, USA.

Purpose: To compare noninvasive transstenotic pressure gradient (TSPG) measurements derived from high-spatial- and temporal-resolution four-dimensional magnetic resonance (MR) flow measurements with invasive measurements obtained from endovascular pressure wires with digital subtraction angiographic guidance.

Materials And Methods: After Animal Care and Use Committee approval, bilateral renal artery stenosis (RAS) was created surgically in 12 swine. Respiratory-gated phase-contrast vastly undersampled isotropic projection (VIPR) MR angiography of the renal arteries was performed with a 1.5-T clinical MR system (repetition time, 11.4 msec; echo time [first echo], 3.7 msec; 18,000 projection angles; imaging volume, 260 × 260 × 200 mm; acquired isotropic spatial resolution, 1.0 × 1.0 × 1.0 mm; velocity encoding, 150 cm/sec). Velocities measured with phase-contrast VIPR were used to calculate TSPGs by using Navier-Stokes equations. These were compared with endovascular pressure measurements (mean and peak) performed by using fluoroscopic guidance with regression analysis.

Results: In 19 renal arteries with an average stenosis of 62% (range, 0%-87%), there was excellent correlation between the noninvasive TSPG measurement with phase-contrast VIPR and invasive TSPG measurement for mean TSPG (R² = 95.4%) and strong correlation between noninvasive TSPG and invasive TSPG for the peak TSPG measures (R² = 82.6%). The phase-contrast VIPR-derived TSPG measures were slightly lower than the endovascular measurements. In four arteries with severe stenoses and one occlusion (mean, 86%; range, 75%-100%), the residual lumen within the stenosis was too small to determine TSPG with phase-contrast VIPR.

Conclusion: The unenhanced MR angiographic technique with phase-contrast VIPR allows for accurate noninvasive assessment of hemodynamic significance in a porcine model of RAS with highly accurate TSPG measurements.
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http://dx.doi.org/10.1148/radiol.11101175DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3184231PMC
October 2011

MR measures of renal perfusion, oxygen bioavailability and total renal blood flow in a porcine model: noninvasive regional assessment of renal function.

Nephrol Dial Transplant 2012 Jan 28;27(1):128-35. Epub 2011 May 28.

Department of Radiology, University of Wisconsin School of Medicine and Public Health, WI, USA.

Background: Magnetic resonance imaging (MRI) may be a useful adjunct to current methods of evaluating renal function. MRI is a noninvasive imaging modality that has the ability to evaluate the kidneys regionally, which is lacking in current clinical methods. Other investigators have evaluated renal function with MRI-based measurements, such as with techniques to measure cortical and medullary perfusion, oxygen bioavailability and total renal blood flow (TRBF). However, use of all three techniques simultaneously, and therefore the relationships between these MRI-derived functional parameters, have not been reported previously.

Methods: To evaluate the ability of these MRI techniques to track changes in renal function, we scanned 11 swine during a state of hyperperfusion with acetylcholine and a saline bolus and subsequently scanned during a state of hypoperfusion with the prolonged use of isoflurane anesthesia. For each time point, measurements of perfusion, oxygen bioavailability and TRBF were acquired. Measurements of perfusion and oxygen bioavailability were compared with measurements of TRBF for all swine across all time points.

Results: Cortical perfusion, cortical oxygen bioavailability, medullary oxygen bioavailability and TRBF significantly increased with the acetylcholine challenge. Cortical perfusion, medullary perfusion, cortical oxygen bioavailability and TRBF significantly decreased during isoflurane anesthesia. Cortical perfusion (Spearman's correlation coefficient = 0.68; P < 1 × 10(-6)) and oxygen bioavailability (Spearman's correlation coefficient = -0.60; P < 0.0001) correlated significantly with TRBF, whereas medullary perfusion and oxygen bioavailability did not correlate with TRBF.

Conclusions: Our results demonstrate expected changes given the pharmacologically induced changes in renal function. Maintenance of the medullary oxygen bioavailability in low blood flow states may reflect the autoregulation particular to this region of the kidney. The ability to non-invasively measure all three parameters of kidney function in a single MRI examination and to evaluate the relationships between these functional parameters is potentially useful for evaluating the state of the human kidneys in situ in future studies.
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http://dx.doi.org/10.1093/ndt/gfr199DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3350337PMC
January 2012

Reproducibility of renal perfusion MR imaging in native and transplanted kidneys using non-contrast arterial spin labeling.

J Magn Reson Imaging 2011 Jun;33(6):1414-21

Department of Medical Physics, University of Wisconsin-Madison, Wisconsin Institute for Medical Research, Madison, Wisconsin 53705-2275, USA.

Purpose: To examine both inter-visit and intra-visit reproducibility of a MR arterial spin labeling (ASL) perfusion technique in native and transplanted kidneys over a broad range of renal function.

Materials And Methods: Renal perfusion exams were performed at 1.5 T in a total of 24 subjects: 10 with native and 14 with transplanted kidneys. Using a flow-sensitive alternating inversion recovery (FAIR) ASL scheme, 32 control/tag pairs were acquired and processed using a single-compartment model. Two FAIR-ASL MR exams were performed at least 24 h apart on all the subjects to assess inter-visit reproducibility. ASL perfusion measurements were also repeated back-to-back within one scanning session in 8 native subjects and in 12 transplant subjects to assess intra-visit reproducibility. Intra-class correlations (ICCs) and coefficients of variation (CVs) were calculated as metrics of reproducibility.

Results: Intra-visit ICCs ranged from 0.96 to 0.98 while CVs ranged from 4.8 to 6.0%. Inter-visit measurements demonstrated slightly more variation with ICCs from 0.89 to 0.94 and CVs from 7.6 to 13.1%. Medullary perfusion demonstrated greater variability compared with cortical blood flow: intra-visit ICCs from 0.72 to 0.78 and CVs from 16.7 to 26.7%, inter-visit ICCs from 0.13 to 0.63 and CVs from 19.8 to 37%.

Conclusion: This study indicates that a FAIR-ASL perfusion technique is reproducible in the cortex of native and transplanted kidneys over a broad range in renal function. In contrast, perfusion measurements in the medulla demonstrated moderate to poor reproducibility for intra-visit and inter-visit measures respectively.
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http://dx.doi.org/10.1002/jmri.22552DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3098463PMC
June 2011
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