[Exposure Dose Reduction for Radiologists with Combination of Angular Beam Modulation and Radiation Protection Drape in CT Fluoroscopy: A Phantom Study].

PURPOSE: To assess the dose reduction of radiologists by using angular beam modulation (ABM) and radiation protection drape during computed tomography (CT) fluoroscopy. MATERIALS AND METHODS: The phantom was set on the lower that is 15 cm from the isocenter position. We measured the radiation exposure around the phantom with radiophotoluminescence glass dosimeters. The space radiation dose rate was measured with an ionization chamber dosimeter in the CT room. RESULTS: The dose rate of finger radiation exposure was 67% at assumed assist tool position with ABM. And the dose rate of finger radiation exposure with the combination of ABM and radiation protection drape was 33%. The space dose rate of exposure with the combination of ABM and radiation protection drape was 49% at 150 cm. CONCLUSION: The combination of ABM and radiation protection drape can reduce finger radiation exposure at assumed assist tool position. The space dose rate of the standing position of radiologists can get a clear dose of radiation reduction by the combination of both.

Optimization method of MRI scan parameters of a double inversion recovery sequence using a T1 map and a developed analysis algorithm.

BACKGROUND: Optimizing scan parameters for double inversion recovery (DIR) sequences remains difficult. OBJECTIVE: To evaluate a new method for optimizing DIR sequence scan parameters using T1 mapping and a newly developed analysis algorithm. METHODS: Twelve healthy volunteers underwent T1 mapping and DIR magnetic resonance imaging. The following steps were used for image optimization including: 1) measurement of gray matter (GM), white matter (WM), and cerebrospinal fluid (CSF) T1 values to create a T1 map; 2) calculation of optimized scan parameters by using a developed analysis algorithm; 3) performance assessment of DIR magnetic resonance imaging by using the calculated optimized imaging parameters. Additionally, we used scan parameters from previous studies to obtain DIR images in order to evaluate our new method. The contrast between GM and suppressed tissues was compared between these images and those obtained using the optimized parameters. RESULTS: Using our optimization method, WM and CSF regions were suppressed uniformly for all scan conditions. The contrast was significantly higher in images obtained using this optimization method compared to those obtained using previously published parameters (p < 0.01). CONCLUSIONS: It is possible to obtain superior DIR images by using an optimization method that involves T1 mapping and a newly developed analysis algorithm.

MTF Measurement of MR Blurring in Liver Dynamic MRI with Gd-EOB-DTPA.

During the arterial phase acquisition of Gd-EOB-DTPA examinations, use of a small volume of the Gd-EOB-DTPA may make it difficult the encoding center of the k-space, and produce blurring. The previous studies revealed the encoding technique of the k-space was one of the most important reasons. However, there is no report to discuss the reasons with quantitative evaluations. The purpose of this study was to quantitatively evaluate the characteristics of the artifacts using different k-space encoding techniques (centric-view ordering (CVO) and sequential-view ordering (SVO)) for liver dynamic MRI in computer simulation study. This simulation study consists of the following steps. First of all, the creation of a time intensity curve, and original simulation images at certain points among the one phase dynamic scanning. Secondly, creation-simulated MR echo data from the created original images using FFT, and encoding simulated k-space using the simulated MR echo data. Finally, a reconstruction of simulated dynamic MR images from the simulated k-space, and to evaluate each simulated MR images, we measured modulation transfer functions (MTFs) from the bar patterns of the reconstructed images. The results of the CVO simulation indicated that the bar patterns were blurring compared to the images encoded by the SVO. The results of the SVO simulation indicated that the bar patterns were not enhanced at late scan timings. In addition, the results of MTFs indicated that there was no edge enhancement at all scan timings and both encoding techniques. In conclusion, it is possible to quantitatively evaluate the characteristics of artifacts using MTF, which was measured by the bar patterns, in liver dynamic MRI.

[Development of an Optimizing Program of Scanning Parameters for Double Inversion Recovery MRI].

The purpose of this study was to develop an optimizing program of scanning parameters for double inversion recovery (DIR) MRI. The optimization algorithm consists of the following steps: (1) obtaining the initial parameters (TR, TE, and T1 values of the two attenuated tissues); (2) iterative calculation for minimization of errors; and (3) determination of the optimized TI(1st) and TI(2nd). To evaluate the developed algorithm, we performed the phantom and simulation studies using the phantoms which were imitated T1 values of white and gray matters and cerebrospinal fluid. In addition, white matter attenuated inversion recovery (WAIR) and gray matter attenuated inversion recovery (GAIR) images were obtained by optimized scan parameters in one volunteer. The developed algorithm could calculate the optimized TI(1st) and TI(2nd) values at once. Results of summation of signal intensity (SI) of two attenuated tissues shows that the SI of the two tissues were well-attenuated using the theoretical values which were calculated using the developed algorithm. The correlation coefficient of the SI of the phantom of the gray matter between actual and simulation measurements was r=0.997. The SI obtained by actual measurements well correlated with the SI obtained by the simulation measurements. The WAIR and GAIR images in the volunteer were well enhanced gray or white matters. We thus conclude that it is possible to calculate the optimized parameters for the DIR-MRI using the developed algorithm.