Publications by authors named "Sabarish Narayanasamy"

13 Publications

  • Page 1 of 1

The Renal Vasculature: What the Radiologist Needs to Know.

Radiographics 2021 Sep-Oct;41(5):1531-1548. Epub 2021 Jul 30.

From the Joint Department of Medical Imaging, University Health Network, Mount Sinai Hospital, and Women's College Hospital, University of Toronto, 200 Elizabeth St, Toronto, ON, Canada M5G 2C4 (A.L., M.J.T., K.K., S.K.); Department of Radiology, University of Iowa, Iowa City, Iowa (S.N.); and Department of Medical Imaging, Ottawa Hospital, University of Ottawa, Ottawa, Ont, Canada (N.S.).

The physiologic role of the kidneys is dependent on the normal structure and functioning of the renal vasculature. Knowledge and understanding of the embryologic basis of the renal vasculature are necessary for the radiologist. Common anatomic variants involving the renal artery (supernumerary arteries and prehilar branching) and renal vein (supernumerary veins, delayed venous confluence, retroaortic or circumaortic vein) may affect procedures like renal transplantation, percutaneous biopsy, and aortic aneurysm repair. Venous compression syndromes (anterior and posterior nutcracker syndrome) can be symptomatic and can be diagnosed with a combination of radiologic features. Renal artery stenosis is commonly atherosclerotic and is diagnosed with Doppler US, CT angiography, or MR angiography. Fibromuscular dysplasia, the second most common cause of renal artery narrowing, has a characteristic string-of-beads appearance resulting from multifocal stenoses and dilatations. Manifestations of renal vasculitis differ depending on whether the affected vessels are large, medium, or small. Renal vascular injury is graded according to the American Association for the Surgery of Trauma (AAST) renal injury scale, which defines and in renal injuries. Both renal arteries and veins are affected by primary neoplasms or secondarily by neoplasms from adjacent structures. Differentiation between bland thrombus and tumor thrombus and the extent of involvement dictate management in malignancies, especially renal cell carcinoma. Aneurysms, pseudoaneurysms, arteriovenous malformations, and arteriovenous fistulas can affect renal vessels and can be diagnosed with specific imaging features. The radiologist has a critical role in identification of specific imaging characteristics and establishing the diagnosis in the varied pathologic conditions affecting the renal vasculature, which is critical for directing management. Thus, the renal vasculature should be an integral part of radiologists' checklist. RSNA, 2021.
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http://dx.doi.org/10.1148/rg.2021200174DOI Listing
July 2021

Factors Affecting Radiation Dose in Computed Tomography Angiograms for Pulmonary Embolism: A Retrospective Cohort Study.

J Clin Imaging Sci 2020 13;10:74. Epub 2020 Nov 13.

Department of Radiology, University of Iowa Hospitals and Clinics, Iowa City, United State.

Objectives: Computed tomography pulmonary angiogram (CTPA) is one of the most commonly ordered and frequently overused tests. The purpose of this study was to evaluate the mean radiation dose to patients getting CTPA and to identify factors that are associated with higher dose.

Material And Methods: This institutionally approved retrospective study included all patients who had a CTPA to rule out acute pulmonary embolism between 2016 and 2018 in a tertiary care center. Patient data (age, sex, body mass index [BMI], and patient location), CT scanner type, image reconstruction methodology, and radiation dose parameters (dose-length product [DLP]) were recorded. Effective dose estimates were obtained by multiplying DLP by conversion coefficient (0.014 mSv•mGy•cm). Multivariate logistic regression analysis was performed to determine the factors affecting the radiation dose.

Results: There were 2342 patients (1099 men and 1243 women) with a mean age of 58.1 years (range 0.2-104.4 years) and BMI of 31.3 kg/m (range 12-91.5 kg/m). The mean effective radiation dose was 5.512 mSv (median - 4.27 mSv; range 0.1-43.0 mSv). Patient factors, including BMI >25 kg/m, male sex, age >18 years, and intensive care unit (ICU) location, were associated with significantly higher dose ( < 0.05). CT scanning using third generation dual-source scanner with model-based iterative reconstruction (IR) had significantly lower dose (mean: 4.90 mSv) versus single-source (64-slice) scanner with filtered back projection (mean: 9.29 mSv, < 0.001).

Conclusion: Patients with high BMI and ICU referrals are associated with high CT radiation dose. They are most likely to benefit by scanning on newer generation scanner using advance model-based IR techniques.
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http://dx.doi.org/10.25259/JCIS_168_2020DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7708960PMC
November 2020

Imaging of COVID-19 pneumonia: Patterns, pathogenesis, and advances.

Br J Radiol 2020 Sep 6;93(1113):20200538. Epub 2020 Aug 6.

Department of Radiology, University of Iowa, Carver College of Medicine, Iowa City, Iowa, USA.

COVID-19 pneumonia is a newly recognized lung infection. Initially, CT imaging was demonstrated to be one of the most sensitive tests for the detection of infection. Currently, with broader availability of polymerase chain reaction for disease diagnosis, CT is mainly used for the identification of complications and other defined clinical indications in hospitalized patients. Nonetheless, radiologists are interpreting lung imaging in unsuspected patients as well as in suspected patients with imaging obtained to rule out other relevant clinical indications. The knowledge of pathological findings is also crucial for imagers to better interpret various imaging findings. Identification of the imaging findings that are commonly seen with the disease is important to diagnose and suggest confirmatory testing in unsuspected cases. Proper precautionary measures will be important in such unsuspected patients to prevent further spread. In addition to understanding the imaging findings for the diagnosis of the disease, it is important to understand the growing set of tools provided by artificial intelligence. The goal of this review is to highlight common imaging findings using illustrative examples, describe the evolution of disease over time, discuss differences in imaging appearance of adult and pediatric patients and review the available literature on quantitative CT for COVID-19. We briefly address the known pathological findings of the COVID-19 lung disease that may help better understand the imaging appearance, and we provide a demonstration of novel display methodologies and artificial intelligence applications serving to support clinical observations.
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http://dx.doi.org/10.1259/bjr.20200538DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7465853PMC
September 2020

Dynamic Contrast-Enhanced MRI-Upgraded Prostate Imaging Reporting and Data System Version 2 Category 3 Peripheral Zone Observations Stratified by a Size Threshold of 15 mm.

AJR Am J Roentgenol 2019 10 23;213(4):836-843. Epub 2019 May 23.

Department of Medical Imaging, The Ottawa Hospital, 1053 Carling Ave, Rm C159, Ottawa, ON K1Y 4E9, Canada.

The purpose of this study is to evaluate dynamic contrast-enhanced (DCE) MRI (DCE-MRI)-upgraded Prostate Imaging Reporting and Data System version 2 (PI-RADSv2) peripheral zone (PZ) observations stratified by a size threshold of 15 mm. Two blinded radiologists independently assessed 301 patients with 326 clinically significant tumors (Gleason score [GS] ≥ 7) using multiparametric MRI performed before radical prostatectomy (RP) between 2012 and 2017 and then assigned PI-RADSv2 scores for the tumors. PI-RADSv2 category 3 PZ observations upgraded on the basis of abnormal DCE-MRI findings were tabulated, agreement was calculated, and discrepancies were resolved by consensus. The rate of detection of clinically significant cancer among upgraded observations was calculated. Size was measured at consensus review and was compared with pathologic outcomes on the basis of the PI-RADSv2 size threshold of 15 mm or more, with the use of chi-square tests. Reader 1 identified 5.2% (17/326) of DCE-MRI-upgraded PZ observations, and reader 2 identified 8.3% (27/326) of such observations. Interobserver agreement for PI-RADSv2 scoring was moderate (κ = 0.42) overall, but it was fair (κ = 0.23) when only DCE-MRI-upgraded observations were considered. Of the upgraded observations, which had a mean (± SD) size of 14 ± 6 mm (range, 6-29 mm), 10.4% (34/326) were agreed on after consensus review. Size smaller than 15 mm was noted for 61.8% (21/34) of observations. Among DCE-MRI-upgraded PZ observations, true- and false-positive detection rates for significant cancer were 91.2% (31/34) and 8.8% (3/34), respectively. Observations 15 mm or larger had no false-positive diagnoses and higher rates of extraprostatic extension (84.6% [11/13] vs 38.1% [8/21]; = 0.016); however, there was no difference in GS ( = 0.354) compared with observations less than 15 mm in size. PZ observations upgraded on the basis of abnormal DCE-MRI findings have a high likelihood of being clinically significant cancer; however, agreement between readers was low. DCE-MRI-upgraded tumors of 15 mm or larger had no false-positive diagnoses and higher rates of extraprostatic extension, suggesting that they could be assigned to PI-RADSv2 assessment category 5.
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http://dx.doi.org/10.2214/AJR.18.21005DOI Listing
October 2019

Diagnostic Accuracy of MRI for Detecting Inferior Vena Cava Wall Invasion in Renal Cell Carcinoma Tumor Thrombus Using Quantitative and Subjective Analysis.

AJR Am J Roentgenol 2019 03 27;212(3):562-569. Epub 2018 Dec 27.

1 Department of Medical Imaging, The Ottawa Hospital, 1053 Carling Ave, Rm C159, Ottawa, ON K1Y 4E9, Canada.

Objective: The purpose of this study is to evaluate MRI in inferior vena cava (IVC) renal cell carcinoma (RCC) tumor thrombus for the diagnosis of caval wall invasion.

Materials And Methods: This retrospective case-control study evaluated 24 consecutive patients who underwent thrombectomy for RCC IVC tumor thrombus (11 [45.8%] with invasion) seen at preoperative MRI. A blinded radiologist segmented tumor thrombus on apparent diffusion coefficient (ADC) maps and T2-weighted images for texture analysis, measured the diameter of the renal vein and IVC at the level of the renal vein ostium, and measured the craniocaudal extent and volume of the tumor thrombus. Two blinded radiologists independently evaluated the margin of the tumor thrombus (smooth vs irregular), thinning or thickening and abnormal T2-weighted signal or enhancement of the IVC wall, and overall impression of invasion. Comparisons were performed using logistic regression models and chi-square with accuracy calculated using ROC.

Results: Subjective features were associated with invasion (p = 0.001-0.045) with moderate-to-substantial agreement (κ = 0.49-0.66). The overall impression of invasion had a sensitivity of 63.6% (95% CI, 30.8-89.1%) and a specificity of 92.3% (95% CI, 64.0-99.8%) with perfect agreement (κ = 1.0). Tumor thrombus with invasion had larger diameters of renal vein (28 ± 8 vs 15 ± 6 mm; p = 0.031) and IVC (41 ± 9 vs 19 ± 6 mm; p = 0.003), greater craniocaudal extent (87 ± 34 vs 51 ± 31 mm; p = 0.0239), and greater volume (77.4 ± 57.6 vs 17.7 ± 17.4 cm; p = 0.003) than did thrombi without invasion. The ROC AUC ranged from 0.78 to 0.83. ADC and texture parameters were not significantly different between groups (p = 0.208-0.503); however, larger entropy in invasive tumor thrombus trended toward significance (p = 0.061). A model combining volume, entropy, and overall impression achieved an AUC of 0.91 (95% CI, 0.77-1.0).

Conclusion: The combination of tumor thrombus volume with entropy and subjective overall impression of IVC wall invasion achieved the highest accuracy for diagnosis.
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http://dx.doi.org/10.2214/AJR.18.20209DOI Listing
March 2019

Encapsulating Peritoneal Sclerosis: The Abdominal Cocoon.

Radiographics 2019 Jan-Feb;39(1):62-77. Epub 2018 Dec 7.

From the Departments of Radiology (M.S., A.L., N.K.), Histopathology (A.B.), General Surgery (T.D.Y.), and Gastroenterology (R.K., S.K.S.), PGIMER, Chandigarh, India; and the Abdominal Imaging Section, Department of Medical Imaging, The Ottawa Hospital, University of Ottawa, Ottawa, Ont, Canada (S.K., S.N., A.M.S.).

Encapsulating peritoneal sclerosis (EPS) is a rare but serious condition that results in (a) encapsulation of bowel within a thickened fibrocollagenous peritoneal membrane and (b) recurrent episodes of bowel obstruction. Although described by various names in the literature, the preferred term is encapsulating peritoneal sclerosis because it best describes the morphologic and histologic changes in this disorder. The etiology of EPS is multifactorial, with a wide variety of implicated predisposing factors that disrupt the normal physiologic function of the peritoneal membrane-prime among these factors being long-term peritoneal dialysis and bacterial peritoneal infections, especially tuberculosis. The clinical features of EPS are usually nonspecific, and knowledge of the radiologic features is necessary to make a specific diagnosis. The findings on radiographs are usually normal. Images from small-bowel follow-through studies show the bowel loops conglomerated in a concertina-like fashion with a serpentine arrangement in a fixed U-shaped configuration. US demonstrates a "cauliflower" appearance of bowel with a narrow base, as well as a "trilaminar" appearance depicted especially with use of high-resolution US probes. CT is the imaging modality of choice and allows identification of the thickened contrast material-enhanced abnormal peritoneal membrane and the encapsulated clumped bowel loops. In addition, CT can potentially help identify the cause of EPS (omental granuloma in tuberculosis), as well as the complications of EPS (bowel obstruction). Conservative medical treatment and surgical therapy early in the course of EPS have been used for management of the condition. The purpose of this article is to review the nomenclature and etiopathogenesis of EPS, describe the multimodality imaging appearances of EPS, including differentiating its features from those of other conditions mimicking EPS, and give an overview of management options. Online DICOM image stacks are available for this article. RSNA, 2018.
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http://dx.doi.org/10.1148/rg.2019180108DOI Listing
March 2020

Evaluation of a free-breathing respiratory-triggered (Navigator) 3-D T1-weighted (T1W) gradient recalled echo sequence (LAVA) for detection of enhancement in cystic and solid renal masses.

Eur Radiol 2019 May 30;29(5):2507-2517. Epub 2018 Nov 30.

The Ottawa Hospital, The University of Ottawa, 1053 Carling Avenue, Ottawa, Ontario, K1Y 4E9, Canada.

Objectives: To evaluate free-breathing Navigator-triggered 3-D T1-weighted MRI (NAV-LAVA) compared to breath-hold (BH)-LAVA among cystic and solid renal masses.

Materials And Methods: With an IRB waiver, 44 patients with 105 renal masses (71 non-enhancing cysts and 14 cystic and 20 solid renal masses) underwent MRI between 2016 and 2017 where BH-LAVA and NAV-LAVA were performed. Subtraction images were generated for BH-LAVA and NAV-LAVA using pre- and 3-min post-gadolinium-enhanced images and were evaluated by two blinded radiologists for overall image quality, image sharpness, motion artifact, and quality of subtraction (using 5-point Likert scales) and presence/absence of enhancement. Percentage signal intensity change (Δ%SI) = ([SI.post-gadolinium-SI.pre-gadolinium]/SI.pre-gadolinium)*100, was measured on BH-LAVA and NAV-LAVA. Likert scores were compared using Wilcoxon's sign-rank test and accuracy for detection of enhancement compared using receiver operator characteristic (ROC) analysis.

Results: Overall image quality (p = 0.002-0.141), image sharpness (p = 0.002-0.031), and motion artifact were better (p = 0.002) comparing BH-LAVA to NAV-LAVA for both radiologists; however, quality of image subtraction did not differ between groups (p = 0.09-0.14). Sensitivity/specificity/area under ROC curve for enhancement in cystic and solid renal masses using subtraction and %SIΔ were (1) BH-LAVA: 64.7%/98.6%/0.82 (radiologist 1), 61.8%/95.8%/0.79 (radiologist 2), and 70.6%/81.7%/0.76 (%SIΔ) versus 2) NAV-LAVA: 58.8%/95.8%/0.79 (radiologist 1, p = 0.16), 58.8%/88.7%/0.73 (radiologist 2, p = 0.37), and 73.5%/76.1%/0.75 (%SIΔ, p = 0.74).

Conclusions: NAV-LAVA showed similar quality of subtraction and ability to detect enhancement compared to BH-LAVA in renal masses albeit with lower image quality, image sharpness, and increased motion artifact. NAV-LAVA may be considered in renal MRI for patients where BH is suboptimal.

Key Points: • Free-breathing Navigator (NAV) 3-D subtraction MRI is comparable to breath-hold (BH) images. • Accuracy for subjective and quantitative diagnosis of enhancement in renal masses on NAV 3-D T1W is comparable to BH MRI. • NAV 3-D T1W renal MRI is useful in patients who may not be able to adequately BH.
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http://dx.doi.org/10.1007/s00330-018-5839-7DOI Listing
May 2019

Radiographic Review of Avulsion Fractures RadioGraphics Fundamentals | Online Presentation.

Radiographics 2018 Sep-Oct;38(5):1496-1497

From the Department of Radiology, Ottawa Hospital, University of Ottawa, 501 Smyth Rd, Ottawa, ON, Canada K1G 4B5 (S.N., S.K., P.S., W.A., A.M.S.); and Department of Medical Imaging, Children's Hospital of Eastern Ontario, Ottawa, Canada (K.K.).

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http://dx.doi.org/10.1148/rg.2018180064DOI Listing
December 2018

Diagnostic Accuracy of MRI for Diagnosis of Internal Hernia in Pregnant Women With Prior Roux-en-Y Gastric Bypass.

AJR Am J Roentgenol 2018 10 14;211(4):755-759. Epub 2018 Aug 14.

3 The Ottawa Hospital, The University of Ottawa, Ottawa, ON, Canada.

Objective: The purpose of this study was to evaluate the accuracy of MRI for the diagnosis of internal hernia (IH) in pregnant women who have undergone Roux-en-Y gastric bypass (RYGB).

Materials And Methods: Fifteen consecutively registered pregnant women (eight with surgically proven IH, seven without IH) who had previously undergone RYGB underwent MRI to rule out IH between July 2011 and July 2016. Two blinded radiologists retrospectively evaluated MRI examinations for the presence or absence of 13 established CT findings of IH. The final diagnosis of IH was evaluated subjectively and with two previously validated CT models (model 1, mesenteric swirl or small-bowel obstruction; model 2, beaking of the superior mesenteric vein or small-bowel obstruction). Diagnostic odds ratio (DOR) and interobserver agreement were calculated for each feature, and the subjective and model-based diagnoses of IH were compared by chi-square test.

Results: There were no statistically significant differences in patient age (p = 0.68), gestational age (p = 0.35), or time since RYGB (p = 0.55) between patients with and those without IH. The findings with best DOR and interobserver agreement were beaking of the superior mesenteric vein (reader 1 DOR, 39; reader 2 DOR, 39; κ = 1.00), mesenteric swirl (reader 1 DOR, 11; reader 2 DOR, 39; κ = 0.86), engorgement of mesenteric vessels (reader 1 DOR, 24; reader 2 DOR, 15; κ = 0.84), and mesenteric edema (reader 1 DOR, 11; reader 2 DOR, 3; κ = 0.73). The other findings had either low accuracy, poor interobserver agreement, or both. The overall sensitivity and specificity of the diagnosis of IH ranged from 75% to 88% and 86% to 100% for the two readers. There was no difference in diagnostic accuracy between the three methods (p = 0.93).

Conclusion: MRI is useful in the diagnosis of IH in pregnant women who have undergone RYGB. The specificity is comparable to that of CT, and the sensitivity approaches that of CT.
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http://dx.doi.org/10.2214/AJR.17.19252DOI Listing
October 2018

Intraventricular migration of an isolated fourth ventricular cysticercus following cerebrospinal fluid shunting.

Surg Neurol Int 2016 5;7(Suppl 39):S952-S954. Epub 2016 Dec 5.

Department of Radiodiagnosis, J N Medical College, Aligarh, India.

Background: Isolated intraventricular neurocysticercosis (NCC) is less frequently seen and can be missed on plain magnetic resonance imaging (MRI). Three-dimensional constructive interference in steady state (CISS) sequence is an extremely helpful sequence in identifying the lesion but is rarely used routinely.

Case Description: Here, we report a case of young male adult who presented with diminution of vision and headache. MRI of the brain revealed hydrocephalus, and on using CISS sequence only, the lesion could be identified in the fourth ventricle. He was treated with medical management, and ventriculoperitoneal shunting of cerebrospinal fluid was done to relieve the hydrocephalus. It resulted in immediate relief with aggravation of headache few days later. Repeat MRI revealed intraventricular migration into the left foramen of monro leading to left lateral ventricle dilatation necessitating endoscopic removal of the lesion.

Conclusion: CISS sequence is definitely the sequence of choice in identifying intraventricular NCC. Ventriculoperitoneal shunting can result in the intraventricular migration of the cyst due to sudden decompression necessitating repeat surgery. Endoscopic removal of NCC has a high success rate with limited complications.
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http://dx.doi.org/10.4103/2152-7806.195232DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5180433PMC
December 2016

Coexistent borderline serous cystadenoma with multifocal hydatidosis in a young female: lessons learnt.

J Med Ultrason (2001) 2016 Oct 17;43(4):553-6. Epub 2016 Jun 17.

Department of Pathology, Faculty of Medicine, Jawaharlal Nehru Medical College and Hospital, Aligarh Muslim University, Aligarh, 202002, UP, India.

Hydatid disease (HD) is a commonly occurring zoonotic disease caused by tapeworms of the genus Echinococcus. It is endemic in many parts of the world and can involve almost any organ of the body. Although HD of the liver and lungs is quite common, ovarian involvement is rare. We present a case of a 24-year-old female patient who was diagnosed with multifocal hydatidosis involving the liver and bilateral ovaries on imaging. Postoperative histopathology confirmed the hydatid disease in the liver and one ovary. However, the cystic lesion in the other ovary turned out to be a borderline serous cystadenoma. This case highlights the limitation of imaging in differentiating between simple hydatid cysts and serous cystadenomas of the ovaries. Another point we learnt is that even in the presence of multifocal hydatidosis in endemic regions, serous cystadenoma needs to be considered in imaging differential diagnosis.
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http://dx.doi.org/10.1007/s10396-016-0727-8DOI Listing
October 2016

Localized acral hypertrophy.

Oman Med J 2015 Jan;30(1):70-1

Department of Radiodiagnosis, Jawaharlal Nehru Medical College and Hospital, AMU, Aligarh, India.

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http://dx.doi.org/10.5001/omj.2015.14DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4371455PMC
January 2015
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