Multidetector CT of pancreas: effects of contrast material flow rate and individualized scan delay on enhancement of pancreas and tumor contrast.

PURPOSE: To prospectively assess whether high contrast material flow rate (8 mL/sec) and individualized scan delay improve enhancement of normal pancreas with multidetector computed tomography (CT) and, as a result, tumor-to-pancreas contrast of pancreatic adenocarcinoma. MATERIALS AND METHODS: Informed consent was obtained in 40 patients (21 women, 19 men; mean age, 67.1 years); the institutional review board approved this protocol. Patients were referred for multidetector CT because they were suspected of having a pancreatic tumor and were randomized to receive 150 mL of nonionic contrast material (300 mg of iodine per milliliter) at a flow rate of 4 mL/sec (n = 21) or 8 mL/sec (n = 19). Patients underwent dynamic scanning at one level every 2 seconds for 66 seconds after intravenous administration of contrast material. Contrast enhancement of pancreas and tumors was measured with circular regions of interest (analysis of variance and Bonferroni-Holm corrected post hoc t tests). RESULTS: Peak contrast enhancement in pancreas was observed significantly earlier (mean +/- standard deviation, 28.7 seconds +/- 3.5 vs 48.2 seconds +/- 5.3; P < .05) and was significantly higher (129.0 HU +/- 25.7 vs 106.2 HU +/- 35.4, P < .05) with a flow rate of 8 mL/sec than with a flow rate of 4 mL/sec. Tumor-to-pancreas contrast greater than 40 HU lasted significantly longer with a flow rate of 8 mL/sec than with a flow rate of 4 mL/sec (26.4 seconds +/- 11.9 vs 8.6 seconds +/- 8.3, P < .05). With a flow rate of 8 mL/sec, an individualized scan delay of 19 seconds after aortic transit time revealed higher tumor-to-pancreas contrast than did a fixed scan delay, and tumor conspicuity was better. CONCLUSION: With 16-section CT, increased contrast material flow rate of 8 mL/sec and individualized scan delay were associated with improved pancreatic enhancement and tumor-to-pancreas contrast compared with flow rate of 4 mL/sec and fixed scan delay.

Computed tomography colonography: feasibility of computer-aided polyp detection in a "first reader" paradigm.

OBJECTIVE: : To determine the feasibility of a computer-aided detection (CAD) algorithm as the "first reader" in computed tomography colonography (CTC). METHODS: : In phase 1 of a 2-part blind trial, we measured the performance of 3 radiologists reading 41 CTC studies without CAD. In phase 2, readers interpreted the same cases using a CAD list of 30 potential polyps. RESULTS: : Unassisted readers detected, on average, 63% of polyps > or =10 mm in diameter. Using CAD, the sensitivity was 74% (not statistically different). Per-patient analysis showed a trend toward increased sensitivity for polyps > or =10 mm in diameter, from 73% to 90% with CAD (not significant) without decreasing specificity. Computer-aided detection significantly decreased interobserver variability (P = 0.017). Average time to detection of the first polyp decreased significantly with CAD, whereas total reading case reading time was unchanged. CONCLUSION: : Computer-aided detection as a first reader in CTC was associated with similar per-polyp and per-patient detection sensitivity to unassisted reading. Computer-aided detection decreased interobserver variability and reduced the time required to detect the first polyp.

Multidetector CT of pancreatic adenocarcinoma: diagnostic advances and therapeutic relevance.

Detection and staging of pancreatic malignancies remains a challenge for radiologists. Considering the poor prognosis of pancreatic adenocarcinoma, accurate preoperative staging is the key to a possibly curative surgical treatment. Contrast-enhanced helical CT has been the most commonly used for evaluation of pancreatic cancer in many institutions, although it suffers from many limitations. With the fast pace of advances in multidetector CT (MDCT), and the beginning clinical implementation of 16-row scanners, improvements in spatial resolution in the z-axis with near-isotropic imaging provide exquisite multiplanar reconstructions of pancreatic anatomy. This article provides an overview of current MDCT technique and protocols for assessment of pancreatic adenocarcinoma, and describes new 3D-display methods for effective visualization of large data sets provided by MDCT.

Effect of contrast dose and field strength in the magnetic resonance detection of brain metastases.

PURPOSE: To compare the diagnostic efficacy of a standard and cumulative triple dose of magnetic resonance (MR) imaging contrast agent in the evaluation of brain metastases using a high-field 3.0 T MR unit versus a standard field 1.5 T MR unit. METHODS: Twenty-two patients with suspected brain metastases were examined at both field strengths using identical postcontrast coronal 3D gradient echo with magnetization preparation, which was adjusted separately for each field strength. In both groups initially, iv injection of 0.1 mmol/kg body weight gadolinium chelate (gadodiamide) and thereafter, 0.2 mmol/kg body weight gadodiamide were administered. Subjective assessment of the images was performed independently by 3 neuroradiologists. Objective measurement of signal-to-noise and contrast-to-noise ratios was obtained. RESULTS: The subjective assessment of cumulative triple-dose 3.0 T images obtained the best results compared with other sequences, detecting 84 metastases, followed by 1.5 T cumulative triple-dose enhanced images with 81 brain metastases. The objective assessment confirmed those results, showing significantly higher signal-to-noise and contrast-to-noise ratios with 3.0 T than with 1.5 T. CONCLUSIONS: Cumulative triple-dose images of both field strengths were superior to standard field strengths. However, administration of gadodiamide contrast agent produces higher contrast between tumor and normal brain on 3.0 T than on 1.5 T, resulting in better detection of brain metastases and leptomeningeal involvement.

Line scan diffusion imaging of the spine.

BACKGROUND AND PURPOSE: Recent findings suggest that diffusion-weighted imaging might be an important adjunct to the diagnostic workup of disease processes in the spine, but physiological motion and the challenging magnetic environment make it difficult to perform reliable quantitative diffusion measurements. Multi-section line scan diffusion imaging of the spine was implemented and evaluated to provide quantitative diffusion measurements of vertebral bodies and intervertebral disks. METHODS: Line scan diffusion imaging of 12 healthy study participants and three patients with benign vertebral compression fractures was performed to assess the potential of line scan diffusion imaging of the spinal column. In a subgroup of six participants, multiple b-value (5-3005 s/mm(2)) images were obtained to test for multi-exponential signal decay. RESULTS: All images were diagnostic and of high quality. Mean diffusion values were (230 +/- 83) x 10(-6) mm(2)/s in the vertebral bodies, (1645 +/- 213) x 10(-6) mm(2)/s in the nuclei pulposi, (837 +/- 318) x 10(-6) mm(2)/s in the annuli fibrosi and ranged from 1019 x 10(-6) mm(2)/s to 1972 x 10(-6) mm(2)/s in benign compression fractures. The mean relative intra-participant variation of mean diffusivity among different vertebral segments (T10-L5) was 2.97%, whereas the relative difference in mean diffusivity among participants was 7.41% (P <.0001). The estimated measurement precision was <2%. A bi-exponential diffusion attenuation was found only in vertebral bodies. CONCLUSION: Line scan diffusion imaging is a robust and reliable method for imaging the spinal column. It does not suffer as strongly from susceptibility artifacts as does echo-planar imaging and is less susceptible to patient motion than are other multi-shot techniques. The different contributions from the water and fat fractions need to be considered in diffusion-weighted imaging of the vertebral bodies.

Local staging of pancreatic carcinoma with multi-detector row CT: use of curved planar reformations initial experience.

PURPOSE: To evaluate the utility of curved planar reformations compared with standard transverse images in the assessment of pancreatic tumors. MATERIALS AND METHODS: Forty-three patients suspected of having pancreatic tumors underwent contrast material-enhanced biphasic multi-detector row computed tomography (CT). Curved planar reformations were generated along the pancreatic duct, common bile duct, and major mesenteric vessels. Three blinded independent readers assessed the curved planar reformations and transverse images separately for the presence of tumor, resectability, and vascular involvement. The results were compared with those of a consensus panel who evaluated the curved planar reformations and transverse images together along with clinical data and surgical findings. RESULTS: Of 43 patients, 20 had pancreatic malignancies as judged by the consensus panel and proven at biopsy and/or clinical follow-up. For tumor detection, transverse images and curved planar reformations had an average sensitivity of 95.0% and 98.4% (P >.05), respectively, and an average specificity of 90.9% and 91.3% (P >.05), respectively. For tumor resectability, transverse images and curved planar reformations had an average sensitivity of 85.7% and 71.4% (P >.05), respectively, and an average specificity of 85.2% and 84.3% (P >.05), respectively. Average interpretation time was 6.4 minutes with transverse images and 4.1 minutes with curved planar reformations. CONCLUSION: Curved planar reformations are equivalent to transverse images in the detection of pancreatic tumors and determination of surgical resectability.

Isoattenuating pancreatic adenocarcinoma at multi-detector row CT: secondary signs.

PURPOSE: To assess the frequency of isoattenuating pancreatic adenocarcinoma with multi-detector row computed tomography (CT) and determine whether there are specific secondary signs that aid in detection. MATERIALS AND METHODS: Fifty-three patients with pancreatic adenocarcinoma underwent contrast material-enhanced biphasic multi-detector row CT with curved planar reformation. Tumors were initially deemed isoattenuating or hypoattenuating to normal pancreatic parenchyma on the basis of visual inspection, and the degree of attenuation was confirmed by calculating the mean attenuation differences between normal pancreatic parenchyma and tumor (tumor-pancreas contrast) during the pancreatic phase. Indirect signs of pancreatic tumor were tabulated in patients with an isoattenuating tumor. RESULTS: Of the 53 patients, six (11%) had isoattenuating tumors with a mean tumor-pancreas contrast of 9.25 HU +/- 11.3 during the pancreatic phase and 4.15 HU +/- 8.5 during the portal venous phase. The secondary signs of pancreatic tumor in these six patients included an interrupted pancreatic duct (n = 5), dilated biliary and pancreatic ducts (n = 1), atrophic distal pancreatic parenchyma (n = 3), and mass effect and/or convex contour abnormality (n = 3). The mean tumor-pancreas contrast for the remaining 47 patients was 74.76 HU +/- 35.61 during the pancreatic phase. CONCLUSION: With no visible tumor-pancreas contrast for isoattenuating tumors, indirect signs such as mass effect, atrophic distal parenchyma, and an interrupted duct sign are important indicators for the presence of tumor.

Diffusion tensor imaging using single-shot SENSE-EPI.

SENSitivity Encoding (SENSE) greatly enhances the quality of diffusion-weighted echo-planar imaging (EPI) by reducing blurring and off-resonance artifacts. Such improvement would also be desirable for diffusion tensor imaging (DTI), but measures derived from the diffusion tensor can be extremely sensitive to any kind of image distortion. Whether DTI is feasible in combination with SENSE has not yet been explored, and is the focus of this study. Using a SENSE-reduction factor of 2, DTI scans in eight healthy volunteers were carried out with regular- and high-resolution acquisition matrices. To further improve the stability of the SENSE reconstruction, a new coil-sensitivity estimation technique based on variational calculus and the principles of matrix regularization was applied. With SENSE, maps of the trace of the diffusion tensor and of fractional anisotropy (FA) had improved spatial resolution and less geometric distortion. Overall, the geometric distortions were substantially removed and a significant resolution enhancement was achieved with almost the same scan time as regular EPI. DTI was even possible without the use of quadrature body coil (QBC) reference scans. Geometry-factor-related noise enhancement was only discernible in maps generated with higher-resolution matrices. Error boundaries for residual fluctuations in SENSE reconstructions are discussed. Our results suggest that SENSE can be combined with DTI and may present an important adjunct for future neuroimaging applications of this technique.

Diffusion-weighted imaging of the spinal cord: interleaved echo-planar imaging is superior to fast spin-echo.

PURPOSE: To compare and evaluate two novel diffusion-weighted sequences, based either on fast spin-echo (FSE) or interleaved echo-planar imaging (EPI) methods, as potential tools for investing spinal cord abnormalities. MATERIALS AND METHODS: Following recent improvements, both interleaved EPI (IEPI) and FSE techniques could be alternative approaches for rapid diffusion-weighted imaging (DWI). Therefore, a navigated diffusion-weighted multishot FSE sequence and a fat-suppressed navigated diffusion-weighted IEPI sequence with local shimming capabilities were tested. Both methods were compared in a consecutive series of five healthy volunteers and five patients with suspected intramedullary lesions. The sequences were graded qualitatively as either superior, inferior, or equal in quality, and also quantitatively by measuring the amount of ghosting artifacts in the background. Quantitative measurements of the diffusion coefficients within the spine were included. RESULTS: The overall image quality of IEPI was superior to FSE. Two out of five FSE scans were rated with poor image quality, whereas all IEPI scans were of sufficient quality. The ghosting levels ranged from approximately 3.3% to 6.2% for IEPI and from approximately 7.5% to 18.9% for FSE. Diffusion coefficients measured in healthy volunteers were similar for both IEPI and FSE, but showed higher fluctuations with the FSE technique. CONCLUSION: Despite potential advantages of FSE, the IEPI technique is preferable for DWI applications in the spinal cord.

CT angiography of the subclavian artery: utility of curved planar reformations.

Despite advances in the diagnosis and treatment of peripheral vascular occlusive disease, an ever-aging population continues to provide scores of new cases requiring medical care. While traditional angiography has been the mainstay of diagnosis for many years, newer, less invasive techniques such as CT angiography with three-dimensional reformation are rapidly establishing themselves as first-line diagnostic modalities. We present a case of severe left subclavian artery stenosis that demonstrates the utility of curved planar reformation in providing a concise visual summary of the pertinent anatomy and abnormalities.

Accuracy of multiphasic helical computed tomography and intraoperative sonography in patients undergoing orthotopic liver transplantation for hepatoma: what is the truth?

OBJECTIVE: To determine the real value of liver imaging in cirrhosis by macro- and histomorphologic examination of the entire organ after orthotopic liver transplantation for hepatocellular carcinoma (HCC). SUMMARY BACKGROUND DATA: In comparative studies, a virtual sensitivity of up to 94% is described for helical computed tomography in HCC staging. The tumor detection rate of intraoperative ultrasonography (IOUS) is reported to be almost 100%. METHODS: This prospective observational study comprised 23 patients with HCC in cirrhosis admitted for orthotopic liver transplantation. Results of preoperative triphasic helical computed tomography (HCT) and IOUS were correlated with histopathologic results after 3-mm-slicing of the explanted liver. RESULTS: Overall, 179 liver segments were examined by HCT, IOUS, and MHM. Fifty-two malignant lesions and 10 dysplastic nodules were revealed by MHM. Using HCT, 13 HCCs could not be identified in 8 patients and 15 results were falsely positive in 10 patients. The detection rate of dysplastic nodes was 40% for HCT and 60% for IOUS. IOUS missed four HCCs in four patients and had six false-positive results in six patients. In a segment-based analysis, the overall accuracy of IOUS was significantly higher for IOUS (95.5%) versus HCT (89.9%). In the lesion-by-lesion analysis, the sensitivity was 92.3% for IOUS and 75.0% for HCT, with a significant difference. CONCLUSIONS: Correlation of explanted liver pathologic results offers precise evaluation of imaging modalities. The data of this histopathologically based study confirm that IOUS is significantly superior in staging HCC in cirrhosis versus CT, even after technical refinements through enhanced multiphasic high-velocity helical scanning.