Prabhakar Rajiah

Imaging of Uncommon Retroperitoneal Masses

Retroperitoneal masses not arising from major solid organs are uncommon. Although there is no simple method of classifying retroperitoneal masses, a reasonable approach is to consider the masses as predominantly solid or cystic and to subdivide these into neoplastic and nonneoplastic masses. Because the treatment options vary, it is useful to be able to differentiate these masses by using imaging criteria. Although the differential diagnosis of retroperitoneal masses can be narrowed down to a certain extent on the basis of imaging characteristics, patterns of involvement, and demographics, there is still a considerable overlap of imaging findings for these masses, and histologic examination is often required for definitive diagnosis. Computed tomography (CT) and magnetic resonance (MR) imaging play an important role in characterization and in the assessment of the extent of the disease and involvement of adjacent and distant structures. Familiarity with the CT and MR imaging features of various retroperitoneal masses will facilitate accurate diagnosis and staging for aggressive lesions.

Utility of High-Resolution MR Imaging in Demonstrating Transmural Pathologic Changes in Crohn Disease

Magnetic resonance (MR) imaging has emerged as an imaging modality that can be used to help diagnose and evaluate Crohn disease of the small and large bowel. MR imaging has high diagnostic accuracy in the detection of Crohn disease, and high-resolution thin-section MR images can demonstrate transmural pathologic changes of Crohn disease from the level of the mucosa to that of the mesentery. High-resolution MR image data also may be used to construct high-quality multiplanar and endoluminal views that may provide additional diagnostic information. Knowledge of the MR imaging findings of Crohn disease and how they correlate with the pathologic features of the disease is important to facilitate accurate diagnosis and detect complications.

Aortic Stiffness Is Increased in Hypertrophic Cardiomyopathy With Myocardial Fibrosis: Novel Insights in Vascular Function From Magnetic Resonance Imaging

OBJECTIVES The aim of the study was to determine if patients with hypertrophic cardiomyopathy (HCM), both with and without myocardial fibrosis, have altered aortic stiffness as assessed by magnetic resonance imaging (MRI) pulse wave velocity (PWV) measurements. BACKGROUND Abnormal aortic stiffness implies an unfavorable prognosis and has been established in a variety of aortic diseases and ischemic cardiomyopathy. However, the relationship between aortic stiffness and HCM has not been studied previously. METHODS The study was institutional review board approved and Health Insurance Portability and Accountability Act of 1996 compliant. Velocity-encoded MRI was performed in 100 HCM and 35 normal control subjects. PWV was determined between the mid-ascending and -descending thoracic aorta. Delayed-enhancement MRI was acquired for identification of myocardial fibrosis. RESULTS Mean age was 52.4 years in HCM and 45.3 years in control subjects. The prevalence of myocardial fibrosis in HCM was 70%. PWV was significantly higher in HCM patients compared with control subjects (8.72 +/- 5.83 m/s vs. 3.74 +/- 0.86 m/s, p < 0.0001). PWV was higher (i.e., increased aortic stiffness) in HCM patients with myocardial fibrosis than in those without (9.66 +/- 6.43 m/s vs. 6.51 +/- 3.25 m/s, p = 0.005). CONCLUSIONS Increased aortic stiffness, as indicated by increased PWV, is evident in HCM patients, and is more pronounced in those with myocardial fibrosis. Further, aortic stiffening may adversely affect left ventricular performance. In addition, increased aortic stiffness correlates with myocardial fibrosis, and may represent another potentially important parameter for risk stratification in HCM, warranting further study.

Diffusion-weighted MR Imaging of the Gastrointestinal Tract: Technique, Indications, and Imaging Findings

Diffusion-weighted magnetic resonance (MR) imaging has emerged as an important tool in the diagnostic work-up of patients with bowel cancer and inflammatory conditions of the gastrointestinal tract. It functions on the basis of the microscopic motion of water molecules in a cellular environment and provides functional information about the water in body tissues. Diffusion-weighted imaging serves to complement conventional MR imaging, and its use may improve the accuracy of tumor detection and staging. It does not rely on the use of intravenous contrast material and may be performed in patients with renal impairment. Because it provides quantitative information about tissue cellularity, diffusion-weighted imaging may be used to distinguish between tissues with altered cellularity (eg, tumors and metastases) and normal tissues. Data from diffusion-weighted MR images enable the calculation of apparent diffusion coefficient (ADC) values, which provide useful information about response to treatment. Malignant gastrointestinal tract tumors have low ADC values, which increase after successful therapy. Diffusion-weighted imaging also plays a role in the evaluation of patients with inflammatory bowel disease and may help assess inflammation and complications, such as abscesses and fistulas. Quantitative measurements of signal intensity at diffusion-weighted imaging may help differentiate actively inflamed bowel from normal bowel, and ADC values provide useful information about disease activity and response to treatment.

Cardiac MR Assessment of Aortic Regurgitation: Holodiastolic Flow Reversal in the Descending Aorta Helps Stratify Severity

PURPOSE To assess the utility of holodiastolic flow reversal (HDR) in the descending aorta on velocity-encoded cardiac magnetic resonance (MR) images in the stratification of aortic regurgitation (AR) severity. MATERIALS AND METHODS This study was approved by the institutional review board, with waiver of informed consent. A total of 80 patients (overall mean age, 49 years ± 18 [standard deviation]; 22 women and 58 men) with clinical indication for cardiac MR imaging of the aorta were analyzed retrospectively. Velocity-encoded MR imaging was used to quantify AR and assess for HDR at the level of the middescending aorta. These indexes were compared with a qualitative integrated echocardiographic evaluation of AR severity. Sensitivity and specificity for HDR in the prediction of substantial AR were determined, and logistic regression analysis (with associated odds ratios and C statistics) was performed, with HDR and regurgitant fraction as independent predictors. An additional 42 patients (overall mean age, 48 years ± 21; 12 female and 30 male) were then prospectively evaluated in similar fashion to evaluate a decision model derived from analysis of the first group. RESULTS HDR predicted severe AR (echo grade, 4) with high sensitivity (100%) and specificity (93%). HDR was highly specific (100%) but had lower sensitivity (61%) for moderate to severe AR (echo grade, 3-4). Integration of HDR and direct AR quantification into a combined stratification model based on analysis of the primary group showed good predictive results in the validation group, with a C statistic of 0.94 for moderate to severe AR and 0.93 for severe AR. CONCLUSION HDR in the middescending thoracic aorta observed at cardiac MR is indicative of severe AR and can be used in conjunction with quantified regurgitant values obtained from velocity-encoded MR imaging to stratify AR severity.

Cardiac MRI: Part 2, Pericardial Diseases

OBJECTIVE MRI plays an important role in the morphologic and functional evaluation of pericardial diseases. MRI has the advantages of high spatiotemporal resolution, soft-tissue contrast, wide FOV, and multiplanar imaging capabilities, making it a valuable tool in the evaluation of pericardial disorders. In this article, the role of MRI in the evaluation of pericardial disorders, including pericardial constriction, is described and illustrated. CONCLUSION MRI is a vital diagnostic tool in the evaluation of pericardial diseases, particularly inflammation and constriction, because it can provide both morphologic and functional information essential for determining the optimal therapeutic strategy. It is used for the characterization and delineation of the extent of spread of pericardial masses. Various imaging sequences are available, so the MRI protocol should be optimized and tailored to the specific clinical condition that is being evaluated.

Computed tomography of the pericardium and pericardial disease.

The spectrum of pericardial abnormalities includes congenital absence, pericardial cyst, pericarditis, effusion, constriction, tamponade, retained foreign body, and neoplasms. Because of it high spatial and temporal resolutions, multiplanar reconstruction capability, and large field of view, computed tomography (CT) is a very useful tool in the comprehensive anatomical and functional evaluation of the pericardium. Knowledge of normal pericardial anatomy, anatomic variants, and imaging appearances of various pericardial abnormalities is essential for accurate diagnoses and characterization. In this pictorial review, the CT appearances of the normal pericardium and pericardial abnormalities are discussed and illustrated.

Cardiovascular MR imaging at 3 T: opportunities, challenges, and solutions.

Although 3-T magnetic resonance (MR) imaging is well established in neuroradiology and musculoskeletal imaging, it is in the nascent stages in cardiovascular imaging applications, and there is limited literature on this topic. The primary advantage of 3 T over 1.5 T is a higher signal-to-noise ratio (SNR), which can be used as such or traded off to improve spatial or temporal resolution and decrease acquisition time. However, the actual gain in SNR is limited by other factors and modifications in sequences adapted for use at 3 T. Higher resonance frequencies result in improved spectral resolution, which is beneficial for fat suppression and spectroscopy. The higher T1 values of tissues at 3 T aid in myocardial tagging, angiography, and perfusion and delayed-enhancement sequences. However, there are substantial challenges with 3-T cardiac MR imaging, including higher magnetic field and radiofrequency inhomogeneities and susceptibility effects, which diminish image quality. Off-resonance artifacts are particularly challenging, especially with steady-state free precession sequences. These artifacts can be managed by using higher-order shimming, frequency scouts, or low repetition times. B1 inhomogeneities can be managed by using radiofrequency shimming, multitransmit coils, or adiabatic pulses. Chemical shifts are also increased at 3 T. The higher radiofrequency results in higher radiofrequency deposition power and a higher specific absorption rate. MR angiography, dynamic first-pass perfusion sequences, myocardial tagging, and MR spectroscopy are more effective at 3 T, whereas delayed-enhancement, flow quantification, and black-blood sequences are comparable at 1.5 T and 3 T. Knowledge of the relevant physics helps in identifying artifacts and modifying sequences to optimize image quality. Online supplemental material is available for this article.

Low-dose, wide-detector array thoracic aortic CT angiography using an iterative reconstruction technique results in improved image quality with lower noise and fewer artifacts

BACKGROUND Iterative reconstruction techniques (IRTs) may improve image quality for low-dose imaging compared with filtered back projection (FBP) reconstruction. OBJECTIVES We compared the results of an IRT for low-dose thoracic aortic computed tomography (CT) imaging with those from FBP reconstruction. METHODS Data from 50 patients who underwent 256-slice CT for evaluation of the thoracic aorta were reconstructed with FBP and an IRT (iDose(4)) at 3 noise-reduction strengths (levels 2, 4, and 6). A blinded reader graded image quality (scale, 1-5; 5 = high diagnostic confidence) and the extent of shoulder artifact (scale, 1-5; 5 = no artifact) on all reconstructions. A second reader evaluated a subset of 20 cases to determine interreader and intrareader reproducibility. The mean and SD of attenuation were measured at 5 locations along the thoracic aorta and both subclavian arteries. RESULTS Image noise (SD of attenuation) improved with IRT relative to FBP (aorta: FBP, 31.4 ± 8.6 HU; IRT level 2, 25.1 ± 6.9 HU; level 4, 21.7 ± 6.2 HU; level 6, 17.2 ± 5.4 HU; P < 0.0001; subclavian arteries: FBP, 92.7 ± 34.6 HU; IRT level 2, 50.1 ± 17.1 HU; level 4, 48.9 ± 18.6 HU; level 6, 45.2 ± 19.2 HU; P < 0.0001), whereas mean attenuation was unchanged. Increasing image quality was observed in the aorta and through the shoulders as the contribution from IRT to the final images increased (P < 0.0001). Significant differences were noted between readers in image quality assessment of the aorta but not through the shoulders. CONCLUSION IRT is associated with reduced noise and shoulder artifact and allows for low-dose aortic CT imaging.

Extramedullary hematopoiesis in unusual locations in hematologically compromised and noncompromised patients.

Extramedullary hematopoiesis (EMH) occurs as a compensatory reaction to an underlying hematologic abnormality. EMH is most commonly seen in the liver and spleen but rarely has been reported in other locations, as well. On rare occasions, EMH may mimic a neoplasm in hematologically noncompromised patients. In this report, we present three cases of EMH in unusual locations, two in the presacral soft tissue and one in the synovial lining of the knee joint. The patients with presacral masses had no hematologic abnormality. In all patients with EMH, imaging plays an important role in both localization of the lesion and guidance for the biopsy; when imaging results are correlated with histological findings, the diagnosis of EMH can be confirmed.