Low-tube-voltage, high-tube-current multidetector abdominal CT: improved image quality and decreased radiation dose with adaptive statistical iterative reconstruction algorithm--initial clinical experience.

PURPOSE: To investigate whether an adaptive statistical iterative reconstruction (ASIR) algorithm improves the image quality at low-tube-voltage (80-kVp), high-tube-current (675-mA) multidetector abdominal computed tomography (CT) during the late hepatic arterial phase. MATERIALS AND METHODS: This prospective, single-center HIPAA-compliant study was institutional review board approved. Informed patient consent was obtained. Ten patients (six men, four women; mean age, 63 years; age range, 51-77 years) known or suspected to have hypervascular liver tumors underwent dual-energy 64-section multidetector CT. High- and low-tube-voltage CT images were acquired sequentially during the late hepatic arterial phase of contrast enhancement. Standard convolution FBP was used to reconstruct 140-kVp (protocol A) and 80-kVp (protocol B) image sets, and ASIR (protocol C) was used to reconstruct 80-kVp image sets. The mean image noise; contrast-to-noise ratio (CNR) relative to muscle for the aorta, liver, and pancreas; and effective dose with each protocol were assessed. A figure of merit (FOM) was computed to normalize the image noise and CNR for each protocol to effective dose. Repeated-measures analysis of variance with Bonferroni adjustment for multiple comparisons was used to compare differences in mean CNR, image noise, and corresponding FOM among the three protocols. The noise power spectra generated from a custom phantom with each protocol were also compared. RESULTS: When image noise was normalized to effective dose, protocol C, as compared with protocols A (P = .0002) and B (P = .0001), yielded an approximately twofold reduction in noise. When the CNR was normalized to effective dose, protocol C yielded significantly higher CNRs for the aorta, liver, and pancreas than did protocol A (P = .0001 for all comparisons) and a significantly higher CNR for the liver than did protocol B (P = .003). Mean effective doses were 17.5 mSv +/- 0.6 (standard error) with protocol A and 5.1 mSv +/- 0.3 with protocols B and C. Compared with protocols A and B, protocol C yielded a small but quantifiable noise reduction across the entire spectrum of spatial frequencies. CONCLUSION: Compared with standard FBP reconstruction, an ASIR algorithm improves image quality and has the potential to decrease radiation dose at low-tube-voltage, high-tube-current multidetector abdominal CT during the late hepatic arterial phase.

Characterization of adrenal lesions: comparison of 2D and 3D dual gradient-echo MR imaging at 3 T--preliminary results.

PURPOSE: To retrospectively compare a two-dimensional (2D) and a three-dimensional (3D) technique for in-phase (IP) and opposed-phase (OP) single-breath-hold 3-T magnetic resonance (MR) imaging in the characterization of adrenal lesions, with histopathologic confirmation, computed tomographic findings, or imaging follow-up for a minimum of 6 months used as the reference standard. MATERIALS AND METHODS: This retrospective HIPAA-compliant study was approved by institutional review board, and a waiver of informed consent was obtained. Thirty-four patients (mean age, 57 years) with 37 adrenal lesions underwent 3-T adrenal MR imaging with both 2D and 3D single-breath-hold dual gradient-echo (GRE) MR sequences. Signal intensity (SI) index and adrenal-to-spleen, adrenal-to-liver, and adrenal-to-muscle SI ratios for each lesion were compared between the two techniques by using repeated-measures analysis of variance. The area under the receiver operating characteristic curve (AUC) for each evaluation method was determined, with retrospective selection of suggested thresholds. RESULTS: For the 2D and 3D techniques, the mean SI index and SI ratios were significantly different between adenomas and nonadenomas (P < .05), except for the adrenal-to-liver SI ratio with the 2D technique and the adrenal-to-muscle SI ratio with both techniques. For all evaluation methods, the AUCs were higher, although not statistically significant, for the 3D technique. The two techniques exploited different suggested thresholds for discriminating adenomas from nonadenomas. CONCLUSION: Adrenal adenomas can be readily differentiated from nonadenomas at 3-T MR imaging with either a 2D or 3D single-breath-hold dual GRE MR technique. Depending on the acquisition technique, different suggested thresholds need to be selected for various evaluation methods.