Novel contrast-injection protocol for high-resolution abdominal CT-angiography: vascular visualization improvement with vasodilator.

PURPOSE: To evaluate the usefulness of a novel contrast-injection protocol for high-resolution abdominal computed tomography angiography (CTA) using nitroglycerin (NTG). METHODS: Abdominal CTA was performed in 80 patients using two 64-detector-row CT scanners. Forty patients were examined after administration of sublingual NTG (NTG group), while 40 were examined without NTG administration (non-NTG group). Arterial phase images were acquired with maximum intensity projection and volume rendering. Reduction rates: vessel cross-sectional areas ratio of 10 cm distal to origin at the superior mesenteric artery, contrast enhancements, signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR) were assessed. Three reviewers evaluated degree of depiction of the peripancreatic vasculature using a four-point scale (1 = poor, 4 = excellent). RESULTS: Reduction rates were significantly lower in the NTG group (P < 0.001), while there were no significant differences in contrast enhancements, SNR, or CNR between groups. Visual evaluation results of the NTG group were significantly better than those of the non-NTG group (P < 0.01). CONCLUSION: Abdominal CTA using NTG improved visualization of the abdominal peripheral vessels. This improved arterial view may be beneficial for preoperative evaluation of the arterial anatomy.

Differential diagnosis of adrenal masses by chemical shift and dynamic gadolinium enhanced MR imaging.

Chemical shift MRI is widely used for identifying adenomas, but it is not a perfect method. We determined whether combined dynamic MRI methods can lead to improved diagnostic accuracy. Fifty-seven adrenal masses were examined by chemical shift and dynamic MR imaging using 2 MR systems. The masses included 38 adenomas and 19 non-adenomas. In chemical shift MRI studies, the signal intensity index (SI) was calculated, and the lesions classified into 5 types in the dynamic MRI studies. Of the 38 adenomas studied, 37 had an SI greater than 0. In the dynamic MRI, 34 of 38 adenomas showed a benign pattern (type 1). If the SI for the adenomas in the chemical shift MRI was considered to be greater than 0, the positive predictive value was 0.9, and the negative predictive value was 0.94 and kappa = 0.79. If type 1 was considered to indicate adenomas in the dynamic MRI, the corresponding values were 0.94, 0.81 and kappa = 0.77 respectively. The results obtained when the 2 methods were combined were 1, 0.95 and kappa = 0.96 respectively. The chemical shift MRI was found to be useful for identifying adenomas in most cases. If the adrenal mass had a low SI (0 < SI < 5), dynamic MRI was also found to be helpful for making a differential diagnosis.

MR imaging of renal cell carcinoma: associations among signal intensity, tumor enhancement, and pathologic findings.

The purpose of this study was to compare the MR characteristics of renal cell carcinomas against histologic findings and to assess the correlations among signal intensity, tumor enhancement, and pathologic findings. Fifty-four patients (56 lesions) were examined by MR imaging and then underwent partial or radical nephrectomy. The pathologic diagnosis of all lesions was renal cell carcinoma. All MR examinations were performed as dynamic studies using the same 1.5-T scanner. MR characteristics were compared against pathologic findings after resection, and the correlations among signal intensity, tumor enhancement, and pathologic findings were then assessed. A significant correlation was observed between tumor grade and tumor enhancement, with G3 lesions tending to show little enhancement. Regardless of the histologic classification, G3 tumors were found to contain highly heterotypic cancer cells and very few vessels by histopathologic examination. No significant correlations were noted between the other MR characteristics and pathologic findings. Renal cell carcinomas showing little enhancement tend to be highly malignant lesions based on the pathologic findings. Special consideration is required for these tumors with regard to the selection of surgical intervention and follow-up observation.

MR imaging of vertebral metastases at 0.2 Tesla: clinical evaluation of T1-weighted opposed-phase gradient-echo imaging.

The purpose of this study was to evaluate clinically T1-weighted spin-echo imaging (T1-SE) and T1-weighted opposed-phase gradient-echo (T1-opposed GRE) in medical examinations for vertebral metastases using 0.2 Tesla MRI. Twenty-one patients (9 males and 12 females, 105 vertebrae) with non-neoplastic lesions were assigned to the normal group (Group N), whereas 27 patients (16 males and 11 females, 133 vertebrae) with malignant metastatic vertebral lesions were assigned to the metastatic group (Group M). Using quantitative analysis, the contrast to noise ratio (CNR) for bone marrow to muscle in the region of interest (ROI) defined by the operator were determined with both groups, whereas the CNR for lesion to bone marrow was determined with Group M. In the subjective analysis, 275 vertebrae of 27 patients in Group M were evaluated. There were significant differences in the Group M between CNR values, T1-SE and T1-opposed GRE. The evaluation by T1-SE image alone was rated as 85.0% for sensitivity, 99.3% for specificity, respectively. On the other hand, evaluation rate only by T1-opposed GRE was 98.5% for sensitivity, 82.4% for specificity, respectively. T1-opposed GRE image is an effective tool for 0.2 Tesla MRI to examine metastatic bone marrow tumors. These findings indicate the necessity of both T1-SE and T1-opposed GRE in diagnostic imaging of vertebral metastases using 0.2 Tesla MRI.

[Study of gradient echo (GRE) Dixon image using low-field MRI scanner for examination of metastatic bone marrow tumors: comparison of double and single echo sequences].

We evaluated the gradient echo (GRE) Dixon method in metastatic bone tumors using a low-field MRI scanner (0.2 Tesla). This method is characterized by the double echo sequence of in-phase and opposed-phase. Studies were carried out on a phantom, 14 healthy volunteers, and clinical examples (33 vertebral bodies) using the T(1)-weighted spin echo, T(2)-weighted turbo spin echo, and GRE Dixon methods. Further, we obtained addition and subtraction images from the double echo sequence. In the clinical examples, the contrast-to-noise ratio (CNR) of the subtraction images (51.3+/-24.1) was significantly better than that of the T(1)-SE images (6.7+/-3.1, p<0.0001). For the examination of metastatic bone marrow tumors using a low-field MRI scanner (0.2 Tesla), subtraction images are thought to be the most effective.