Quantification of Liver Iron Overload with MRI: Review and Guidelines from the ESGAR and SAR.

Accumulation of excess iron in the body, or systemic iron overload, results from a variety of causes. The concentration of iron in the liver is linearly related to the total body iron stores and, for this reason, quantification of liver iron concentration (LIC) is widely regarded as the best surrogate to assess total body iron. Historically assessed using biopsy, there is a clear need for noninvasive quantitative imaging biomarkers of LIC. MRI is highly sensitive to the presence of tissue iron and has been increasingly adopted as a noninvasive alternative to biopsy for detection, severity grading, and treatment monitoring in patients with known or suspected iron overload. Multiple MRI strategies have been developed in the past 2 decades, based on both gradient-echo and spin-echo imaging, including signal intensity ratio and relaxometry strategies. However, there is a general lack of consensus regarding the appropriate use of these methods. The overall goal of this article is to summarize the current state of the art in the clinical use of MRI to quantify liver iron content and to assess the overall level of evidence of these various methods. Based on this summary, expert consensus panel recommendations on best practices for MRI-based quantification of liver iron are provided.

Lung and kidney perfusion deficits diagnosed by dual-energy computed tomography in patients with COVID-19-related systemic microangiopathy.

OBJECTIVES: There is increasing evidence that thrombotic events occur in patients with coronavirus disease (COVID-19). We evaluated lung and kidney perfusion abnormalities in patients with COVID-19 by dual-energy computed tomography (DECT) and investigated the role of perfusion abnormalities on disease severity as a sign of microvascular obstruction. METHODS: Thirty-one patients with COVID-19 who underwent pulmonary DECT angiography and were suspected of having pulmonary thromboembolism were included. Pulmonary and kidney images were reviewed. Patient characteristics and laboratory findings were compared between those with and without lung perfusion deficits (PDs). RESULTS: DECT images showed PDs in eight patients (25.8%), which were not overlapping with areas of ground-glass opacity or consolidation. Among these patients, two had pulmonary thromboembolism confirmed by CT angiography. Patients with PDs had a longer hospital stay (p = 0.14), higher intensive care unit admission rates (p = 0.02), and more severe disease (p = 0.01). In the PD group, serum ferritin, aspartate aminotransferase, fibrinogen, D-dimer, C-reactive protein, and troponin levels were significantly higher, whereas albumin level was lower (p < 0.05). D-dimer levels ≥ 0.485 µg/L predicted PD with 100% specificity and 87% sensitivity. Renal iodine maps showed heterogeneous enhancement consistent with perfusion abnormalities in 13 patients (50%) with lower sodium levels (p = 0.03). CONCLUSIONS: We found that a large proportion of patients with mild-to-moderate COVID-19 had PDs in their lungs and kidneys, which may be suggestive of the presence of systemic microangiopathy with micro-thrombosis. These findings help in understanding the physiology of hypoxemia and may have implications in the management of patients with COVID-19, such as early indications of thromboprophylaxis or anticoagulants and optimizing oxygenation strategies. KEY POINTS: • Pulmonary perfusion abnormalities in COVID-19 patients, associated with disease severity, can be detected by pulmonary DECT. • A cutoff value of 0.485 µg/L for D-dimer plasma levels predicted lung perfusion deficits with 100% specificity and 87% sensitivity (AUROC, 0.957). • Perfusion abnormalities in the kidney are suggestive of a subclinical systemic microvascular obstruction in these patients.

Pathology associated with adherent perirenal fat and its clinical effect.

INTRODUCTION: The dissection of perirenal fat is of critical importance to kidney surgery and ease of dissection is more important when using minimally invasive approaches. This study aimed to determine the clinical, radiological, and pathological significance of adherent perirenal fat (APF). MATERIALS AND METHODS: This prospective study included 22 patients scheduled for partial nephrectomy and 40 patients for donor nephrectomy. Intraoperative fat dissection time was recorded, and the complexity of perirenal fat dissection was surgeon-classified as easy, moderate, and difficult. Perirenal fat and subcutaneous fat thickness were measured. Measurement of perirenal fat depth and the Hounsfield unit (HU) for both perirenal and subcutaneous fields were performed using computed tomography (CT) images. All specimens were submitted for histopatological analysis. Researchers in each arm were blinded to other researchers' data. RESULTS: Mean age of the patients was 51.3 ± 12.7 years. Mean perirenal fat dissection time was 15.0 ± 13.5 minutes. Patient demographics, BMI, nor occupational status differed between the 3 complexity of perirenal fat dissection groups. Radiological findings showed that there was a significant correlation between perirenal fat depth and complexity of perirenal fat dissection (P < .05), but not with HU measurements or subcutaneous fat thickness. Surgeon classification of the complexity of perirenal fat dissection was in accordance with the duration of dissection (P < .05). Perinephric fat contained more fibrous tissue in the patients with histologically proven APF than in those without (P < .05). CONCLUSIONS: APF is a challenge during kidney surgery. Difficult dissection prolongs the duration of perirenal fat dissection and surgery. Perirenal fat thickness measured via preoperative CT might be used to predict APF.

A sling of a normal right inferior vena cava around the abdominal aorta.

Variations in the anatomy of inferior vena cava (IVC) may have important clinical implications. In-depth knowledge of its embryology and variations are of fundamental importance to prevent any potential medical complications related to anatomic variations of the IVC. In this article, we described a previously unreported, to the best of our knowledge, a variation of IVC. In the case we presented, the IVC was seen almost completely encircling the abdominal aorta. We decided to call this anatomic variation as "a sling of a normal right IVC around the abdominal aorta". Cross-sectional imaging is a prompt and highly reliable method to evaluate IVC anatomy and may have significant clinical importance to prevent any potential complications related to IVC during surgery or interventional radiology procedures.

Tissue fat quantification by magnetic resonance imaging: proton density fat fraction in polycystic ovary syndrome.

RESEARCH QUESTION: What are the potential differences between lean women with and without polycystic ovary syndrome (PCOS) in fat content in liver, vertebrae, paraspinal muscles, pancreas, subcutaneous (SCAT) and visceral adipose tissue (VAT)? Magnetic resonance imaging proton density fat fraction (PDFF) was used to establish these differences. This is a novel, non-invasive, operator-independent method with comparable diagnostic sensitivity and specificity to histologic examination for fatty liver disease, and strong correlation with muscle strength in neuromuscular studies. DESIGN: Twenty lean women with PCOS (mean age 23.9 ± 2.3; body mass index [BMI] 22.4 ± 2.0) and 20 age- and BMI-matched healthy women (mean age 24.9 ± 1.5; BMI 21.5 ± 1.9) were enrolled in this cross-sectional study. Anthropometric, biochemical and hormonal evaluations along with magnetic resonance imaging proton density fat fraction were carried out. RESULTS: PDFF% measurements of liver, SCAT and VAT were higher in the PCOS group, indicating increased fat content in these areas in lean women with PCOS compared with controls (P = 0.045, 0.030 and 0.037, respectively). In contrast, PDFF% values of vertebrae and paraspinal muscles in the PCOS group were lower than controls (P = 0.038 and 0.05, respectively). Pancreatic PDFF% measurements were similar between the groups. In the PCOS group, PDFF% of VAT was positively correlated with free androgen index (r = 0.69, P = 0.002). CONCLUSIONS: PDFF% measurement, an MRI-based novel biomarker, reveals increased fat in liver, SCAT and VAT, and decreased fat in vertebral bones and paraspinal muscles of lean women with PCOS.

Prostatitis, the Great Mimicker of Prostate Cancer: Can We Differentiate Them Quantitatively With Multiparametric MRI?

OBJECTIVE. The purpose of this study was to investigate the diagnostic performance of semiquantitative and quantitative pharmacokinetic parameters and quantitative apparent diffusion coefficient (ADC) values obtained from prostate multiparametric MRI (mpMRI) to differentiate prostate cancer (PCa) and prostatitis objectively. MATERIALS AND METHODS. We conducted a retrospective review of patients with biopsy-proven PCa or prostatitis who underwent mpMRI study between January 2015 and February 2018. Mean ADC, forward volume transfer constant (Ktrans), reverse volume transfer constant (kep), plasma volume fraction (Vp), extravascular extracellular space volume fraction (Ve), and time to peak (TTP) values were calculated for both lesions and contralateral normal prostate tissue. Signal intensity-time curves were analyzed. Lesion-to-normal prostate tissue ratios of pharmacokinetic parameters were also calculated. The diagnostic accuracy and cutoff points of all parameters were analyzed to differentiate PCa from prostatitis. RESULTS. A total of 138 patients (94 with PCa and 44 with prostatitis) were included in the study. Statistically, ADC, quantitative pharmacokinetic parameters (Ktrans, kep, Ve, and Vp), their lesion-to-normal prostate tissue ratios, and TTP values successfully differentiated PCa and prostatitis. Surprisingly, we found that Ve values were significantly higher in prostatitis lesions. The combination of these parameters had 92.7% overall diagnostic accuracy. ADC, kep, and TTP made up the most successful combination for differential diagnosis. Analysis of the signal intensity-time curves showed mostly type 2 and type 3 enhancement curve patterns for patients with PCa. Type 3 curves were not seen in any prostatitis cases. CONCLUSION. Quantitative analysis of mpMRI differentiates PCa from prostatitis with high sensitivity and specificity, appears to have significant potential, and may improve diagnostic accuracy. In addition, evaluating these parameters does not cause any extra burden to the patients.

RSNA Committee on International Radiology Education: 25 Years of Global Education Outreach.

The Radiological Society of North America (RSNA) Committee on International Radiology Education (CIRE) has worked for the past 25 years to create academic programs oriented to the needs of international radiologists. The CIRE develops organized and structured approaches to help build one's capabilities and increase one's capacity for professional growth, which then facilitates better patient care. The authors describe the four programs that CIRE is responsible for and introduces its newest initiative, Global Learning Centers, which is planned to start in 2021. RSNA involvement in global radiology education provides opportunities for early, mid-, and late-career radiologists to participate in these programs as students or teachers. The authors describe some of the programs' success stories and invite readers to become a part of and contribute to the growth of radiologic academic endeavors globally. ©RSNA, 2020.

Imaging findings of congenital anomalies of seminal vesicles.

The seminal vesicles are paired organs of the male reproductive tract, which produce and secrete seminal fluid. Although congenital anomalies of seminal vesicles are usually asymptomatic, they may lead to various urogenital symptoms, including infertility. Due to their embryologic relationship with other urogenital organs, congenital anomalies of seminal vesicles may accompany other urinary or genital anomalies. Congenital anomalies of seminal vesicles include agenesis, hypoplasia, duplication, fusion, and cyst. These anomalies can be diagnosed with various imaging techniques. The main purpose of this article is to summarise imaging findings and clinical importance of congenital anomalies of seminal vesicles with images of some rare and previously unreported anomalies.

Primary retroperitoneal fasciitis; A rare cause of acute abdominal pain.

The retroperitoneal fascial planes can be affected by various clinical disorders. In most of the cases retroperitoneal involvement occurs secondary to spread of a distinct underlying etiology. Herein we report two cases of primary retroperitoneal fasciitis diagnosed with imaging findings. The diagnosis of retroperitoneal fasciitis should be made by exclusion since various and more frequently encountered disorders including acute pancreatitis, duodenitis, pyelonephritis, and appendicitis may present with similar imaging findings.

Hepatobiliary Tuberculosis: Imaging Findings.

OBJECTIVE: Tuberculosis (TB) may present with highly variable imaging findings. The findings may vary from nonspecific hepatomegaly to abscesses or solid focal lesions, mimicking liver tumors. Biliary tract involvement may also be detected, which may manifest with ductal dilatations from underlying strictures. CONCLUSION: All cross-sectional imaging modalities, including sonography, CT, and MRI, may be used in the evaluation of patients with TB. Imaging findings may be perplexing to radiologists, particularly ones who practice in areas where TB is not endemic; thus, histopathologic diagnosis may be required.

A comparison of liver fat content as determined by magnetic resonance imaging-proton density fat fraction and MRS versus liver histology in non-alcoholic fatty liver disease.

BACKGROUND: Many imaging methods have been defined for quantification of hepatic steatosis in non-alcoholic fatty liver disease (NAFLD). However, studies comparing the efficiency of magnetic resonance imaging-proton density fat fraction (MRI-PDFF), magnetic resonance spectroscopy (MRS), and liver histology for quantification of liver fat content are limited. PURPOSE: To compare the efficiency of MRI-PDFF and MRS in the quantification of liver fat content in individuals with NAFLD. MATERIAL AND METHODS: A total of 19 NAFLD patients underwent MRI-PDFF, MRS, and liver biopsy for quantification of liver fat content. The MR examinations were performed on a 1.5 HDx MRI system. The MRI protocol included T1-independent volumetric multi-echo gradient-echo imaging with T2* correction and spectral fat modeling and MRS with STEAM technique. RESULTS: A close correlation was observed between liver MRI-PDFF- and histology- determined steatosis (r = 0.743, P < 0.001) and between liver MRS- and histology-determined steatosis (r = 0.712, P < 0.001), with no superiority between them (ƶ = 0.19, P = 0.849). For quantification of hepatic steatosis, a high correlation was observed between the two MRI methods (r = 0.986, P < 0.001). MRI-PDFF and MRS accurately differentiated moderate/severe steatosis from mild/no hepatic steatosis (P = 0.007 and 0.013, respectively), with no superiority between them (AUCMRI-PDFF = 0.881 ± 0.0856 versus AUCMRS = 0.857 ± 0.0924, P = 0.461). CONCLUSION: Both MRI-PDFF and MRS can be used for accurate quantification of hepatic steatosis.

Does coronary calcium scoring with a SCORE better predict significant coronary artery stenosis than without? Correlation with computed tomography coronary angiography.

OBJECTIVE: To determine effectiveness of coronary artery calcium score (CACS) alone and combined with Systematic Coronary Risk Evaluation (SCORE) in adult patients for significant coronary artery stenosis by using computed tomography coronary angiography (CTCA) as reference standard. METHODS: Two thousand twenty-one patients with suspected coronary artery disease (CAD) underwent CACS test and CTCA. Patients were examined with dual-source CT and were grouped according to their age, gender, CACS, and estimated SCORE risk. Coronary plaque existence and degree of stenosis were assessed with CTCA. Sensitivity, specificity, and ROC curves were analyzed. RESULTS: CACS was the single independent variable in estimating relative risk of critical stenosis and had superior outcome when compared with SCORE risk in logistic regression and ROC curve. Area under the ROC curve was greatest in the interval between 50-59 years. When SCORE was combined with CACS in patients with zero CACS, percentage of significant stenosis increased from 1.4% to 7.0% in patients with high or very high SCORE risk, and decreased to 0.9 % in patients with low or moderate SCORE risk. CONCLUSIONS: CACS combination with SCORE risk predicts coronary artery stenosis. When CACS is zero, CTCA can be performed in patients with high or very high SCORE risk.

Imaging of hepatobiliary involvement in sarcoidosis.

Sarcoidosis is mainly a disease of the respiratory system; however, several other organ systems may be affected in the course of the disease. Liver is one of the most frequently affected organs in the setting of sarcoidosis after lungs and lymph nodes. Microscopic hepatic involvement is common in these patients but is mostly clinically silent. However, in a significant portion of these patients, macroscopic findings can be detected in the course of the disease, and these findings may easily be confused with other benign and malignant conditions of the liver. The purposes of this article are to briefly summarize the clinical findings and the underlying pathophysiology of sarcoidosis and detailed presentation of the radiologic findings of hepatic involvement in this disease. We subgrouped the imaging findings based on the location and the radiologic appearance of the hepatic involvement. We tried to provide images that would enable the readers to link the imaging findings with the underlying pathology and clinical symptoms.

Quantification of liver, pancreas, kidney, and vertebral body MRI-PDFF in non-alcoholic fatty liver disease.

PURPOSE: The purpose of the present study was to determine liver, pancreas, kidney, and vertebral fat deposition in NAFLD patients by proton density fat fraction (PDFF) using magnetic resonance imaging (MRI) and to evaluate the relationships among them. METHODS: A total of 41 biopsy-proven NAFLD patients underwent MRI-PDFF with IDEAL-IQ. MRI protocol included T1-independent volumetric multi-echo gradient-echo imaging with T2* correction and spectral fat modeling. The MR examinations were performed on a 1.5 HDx MRI system. MRI-PDFF measurements were obtained from liver, pancreas, renal cortex and sinus, and vertebral body. Liver biopsy specimens were retrieved from the archives and evaluated by one pathologist according to NASH CRN. RESULTS: The median age of the patients was 47 years. The median interval between liver biopsy and MRI examination was 16 days. Mean liver, pancreas, renal cortex, renal sinus, T12 and L1 vertebral body MRI-PDFFs were 18.7%, 5.7%, 1.7%, 51%, 43.2%, and 43.5%, respectively. No correlation between either liver MRI-PDFF or histological steatosis, and other organ MRI-PDFFs was observed. A good correlation between pancreas and vertebral body MRI-PDFFs, and pancreas and renal sinus MRI-PDFFs was observed. Diabetic patients had higher average pancreas MRI-PDFF compared to non-diabetics (12.2%, vs., 4.8%; P = 0.028). CONCLUSIONS: Pancreas and vertebral body MRI-PDFF is well correlated in NAFLD patients and both of them are higher in diabetic patients which may explain increased bone fractures in diabetics. MRI-PDFF can be used to demonstrate fat fractions of different organs and tissues and to understand fat metabolism.

Impact of sequential proton density fat fraction for quantification of hepatic steatosis in nonalcoholic fatty liver disease.

OBJECTIVE: To determine the utility of sequential MRI-estimated proton density fat fraction (MRI-PDFF) for quantification of the longitudinal changes in liver fat content in individuals with nonalcoholic fatty liver disease (NAFLD). METHODS: A total of 18 consecutive individuals (M/F: 10/8, mean age: 47.7±9.8 years) diagnosed with NAFLD, who underwent sequential PDFF calculations for the quantification of hepatic steatosis at two different time points, were included in the study. All patients underwent T1-independent volumetric multi-echo gradient-echo imaging with T2* correction and spectral fat modeling. RESULTS: A close correlation for quantification of hepatic steatosis between the initial MRI-PDFF and liver biopsy was observed (rs=0.758, p<0.001). The median interval between two sequential MRI-PDFF measurements was 184 days. From baseline to the end of the follow-up period, serum GGT level and homeostasis model assessment score were significantly improved (p=0.015, p=0.006, respectively), whereas BMI, serum AST, and ALT levels were slightly decreased. MRI-PDFFs were significantly improved (p=0.004). A good correlation between two sequential MRI-PDFF calculations was observed (rs=0.714, p=0.001). With linear regression analyses, only delta serum ALT levels had a significant effect on delta MRI-PDFF calculations (r2=38.6%, p=0.006). At least 5.9% improvement in MRI-PDFF is needed to achieve a normalized abnormal ALT level. The improvement of MRI-PDFF score was associated with the improvement of biochemical parameters in patients who had improvement in delta MRI-PDFF (p<0.05). CONCLUSIONS: MRI-PDFF can be used for the quantification of the longitudinal changes of hepatic steatosis. The changes in serum ALT levels significantly reflected changes in MRI-PDFF in patients with NAFLD.

Applications of dual-energy CT in emergency radiology.

OBJECTIVE: Recent technologic advances in MDCT have led to the introduction of dual-energy CT (DECT). The basic principle of DECT is to acquire images at two different energy levels simultaneously and to use the attenuation differences at these different energy levels for deriving additional information, such as virtual monochromatic images, artifact suppression, and material composition of various tissues. CONCLUSION: A variety of image reconstruction and postprocessing techniques are available for better demonstration and characterization of pathologic abnormalities. DECT can provide both anatomic and functional information of different organ systems. This article focuses on the main applications of DECT in emergency radiology.

Marked difference in liver fat measured by histology vs. magnetic resonance-proton density fat fraction: A meta-analysis.

Background & Aims: Pathologists quantify liver steatosis as the fraction of lipid droplet-containing hepatocytes out of all hepatocytes, whereas the magnetic resonance-determined proton density fat fraction (PDFF) reflects the tissue triacylglycerol concentration. We investigated the linearity, agreement, and correspondence thresholds between histological steatosis and PDFF across the full clinical spectrum of liver fat content associated with non-alcoholic fatty liver disease. Methods: Using individual patient-level measurements, we conducted a systematic review and meta-analysis of studies comparing histological steatosis with PDFF determined by magnetic resonance spectroscopy or imaging in adults with suspected non-alcoholic fatty liver disease. Linearity was assessed by meta-analysis of correlation coefficients and by linear mixed modelling of pooled data, agreement by Bland-Altman analysis, and thresholds by receiver operating characteristic analysis. To explain observed differences between the methods, we used RNA-seq to determine the fraction of hepatocytes in human liver biopsies. Results: Eligible studies numbered 9 (N = 597). The relationship between PDFF and histology was predominantly linear (r = 0.85 [95% CI, 0.80-0.89]), and their values approximately coincided at 5% steatosis. Above 5% and towards higher levels of steatosis, absolute values of the methods diverged markedly, with histology exceeding PDFF by up to 3.4-fold. On average, 100% histological steatosis corresponded to a PDFF of 33.0% (29.5-36.7%). Targeting at a specificity of 90%, optimal PDFF thresholds to predict histological steatosis grades were ≥5.75% for ≥S1, ≥15.50% for ≥S2, and ≥21.35% for S3. Hepatocytes comprised 58 ± 5% of liver cells, which may partly explain the lower values of PDFF vs. histology. Conclusions: Histological steatosis and PDFF have non-perfect linearity and fundamentally different scales of measurement. Liver fat values obtained using these methods may be rendered comparable by conversion equations or threshold values. Impact and implications: Magnetic resonance-proton density fat fraction (PDFF) is increasingly being used to measure liver fat in place of the invasive liver biopsy. Understanding the relationship between PDFF and histological steatosis fraction is important for preventing misjudgement of clinical status or treatment effects in patient care. Our analysis revealed that histological steatosis fraction is often significantly higher than PDFF, and their association varies across the spectrum of fatty liver severity. These findings are particularly important for physicians and clinical researchers, who may use these data to interpret PDFF measurements in the context of histologically evaluated liver fat content.

Hepatic steatosis: quantification by proton density fat fraction with MR imaging versus liver biopsy.

PURPOSE: To determine utility of proton density fat fraction (PDFF) measurements for quantifying the liver fat content in patients with nonalcoholic fatty liver disease (NAFLD), and compare these results with liver biopsy findings. MATERIALS AND METHODS: This retrospective study was approved by the institutional review board with waivers of informed consent. Between June 2010 and April 2011, 86 patients received a diagnosis of NAFLD. Ten patients did not accept liver biopsy and six patients had contraindications for magnetic resonance (MR) imaging. Seventy patients were included in this study. Seventy patients with NAFLD (40 men, 30 women; mean age, 44.7 years; range, 16-69 years) underwent T1-independent volumetric multiecho gradient-echo imaging with T2* correction and spectral fat modeling. Median time interval between MR imaging and liver biopsy was 14.5 days (range, 0-259 days). MR examinations were performed with a 1.5-T MR imaging system. Complex-based PDFF measurements were performed by placing regions of interest in Couinaud system segments V-VI and all liver segments from I to VIII. All liver biopsy specimens were retrieved from archives and evaluated by one pathologist for hepatic steatosis according to criteria from a previous study. Pearson correlation coefficient, receiver operating characteristics, and linear regression analyses were used for statistical analyses. RESULTS: Mean PDFF calculated with MR imaging was 18.1% ± 9.5 (standard deviation). Close correlation for quantification of hepatic steatosis was observed between PDFF and liver biopsy (r = 0.82). PDFF was effective in discriminating moderate or severe hepatic steatosis from mild or no hepatic steatosis, with area under the curve of 0.95. The correlation between biopsy and PDFF-determined steatosis was less pronounced when fibrosis was present (r = 0.60) than when fibrosis was absent (r = 0.86; P = .02). CONCLUSION: PDFF measurement by MR imaging provided a noninvasive, accurate estimation of the presence and grading of hepatic steatosis in patients with NAFLD. Hepatic fibrosis reduced the correlation between biopsy results and PDFF.