Peripheral MRA with continuous table movement: imaging speed and robustness compared to a conventional stepping table technique.

PURPOSE: To investigate the potential of continuous table movement (CTM)-MRA for reduction of acquisition time and to evaluate the image quality in comparison to conventional stepping table (CST) MRA. MATERIALS AND METHODS: The data of 82 patients were included in this retrospective, IRB-approved study. All patients underwent peripheral MRA at our institution. 41 consecutive patients were examined with a CST-MRA at a 1.5 T MR system. 41 different consecutive patients were examined with a CTM-MRA at 3.0 T MR system. Image quality was assessed by two independent radiologists in consensus on a 4-point Likert-type scale. Descriptive statistics and t-tests were used to compare image acquisition time of CST-MRA to that of CTM-MRA with and without additional time-resolved imaging of the feet using the TWIST technique. Additionally, acquisition time was compared in a subgroup of the fastest 50%. RESULTS: The mean imaging time for the CTM-MRA was 34% less than with the CST-MRA (18.2 min vs. 27.5 min; p<0.0001). Even with inclusion of the TWIST sequence the combined CTM-/TWIST-MRA protocol was 26% faster (20.3 min vs. 27.5 min; p<0.0001). The image quality was slightly better with CTM-MRA (CTM-MRA mean score 3.3±0.5, mean score CST-MRA 2.9±0.6). Venous overlay was significantly lower using the CTM-MRA approach (CTM-MRA mean score 2.8±0.4; CST-MRA mean score 2.2±0.7; p<0.0001). CONCLUSION: CTM-MRA is on average 30% faster than a comparable CST-MRA protocol with equal image quality. Even when adding an additional time-resolved-MRA of the calf station the CTM-MRA protocol is still 26% faster. In conclusion, this study proves that CTM-MRA further improves MRA by reducing user interference and image acquisition times and hence allowing to increase the clinical throughput.

8-bit or 11-bit monochrome displays--which image is preferred by the radiologist?

OBJECTIVES: Vendors of medical displays promise a better diagnostic performance using 10- or 11-bit instead of 8-bit monochrome displays. We measured the gain of "Just Noticeable Difference" (JND) steps using high grayscale resolutions and evaluated the preference of radiologists regarding different aspects of image quality. METHODS: The amount of JND steps was measured on a display using 8-, 10- and 11-bit Look Up Tables (LUT). Radiological images were presented simultaneously using an 8-bit and an 11-bit LUT, radiologists where asked to determine the better image presentation regarding quality parameters like sharpness, contrast and detectability of details. RESULTS: The 10-bit technology realized more than twice the number of JND steps compared to an 8-bit LUT, an 11-bit LUT presented only few additional JND steps. The radiologists did not attest the higher grayscale resolution a better image quality, they regarded the 8-bit technology to show a better sharpness and contrast, although this had no impact on the detectability of details. CONCLUSIONS: Our measurements confirmed that the higher grayscale resolution results in a more complete visualization of image information. But radiologists partially judged this as a lack of sharpness and contrast and generally preferred the 8-bit display.