[Investigation of Changing Imaging Contrast Using Compressed Sensing in Gd-EOB-DTPA Hepatocyte Phase].

In recent years, gadolinium ethoxybenzyl diethylenetriamine pantaacetic acid (Gd-EOB-DTPA) has been commonly used in magnetic resonance imaging (MRI) for liver contrast studies. The purpose of this study was to investigate the effect of Hyper SENSE factor on contrast in the Gd-EOB-DTPA hepatocyte phase. The subjects were 21 patients [16 males and 5 females, aged 50-94 years (mean age 68±12years)] who underwent hepatic contrast-enhanced MRI with Gd-EOB-DTPA from March 2021 to December 2021. The contrast ratios (CRs) of liver/spleen and liver/tumor were measured when the Hyper SENSE factor was changed to 1.0, 1.4 and 1.8. As a result, there was no statistically significant difference in signal intensity and CR with the change in the Hyper SENSE factor. In this study, the acquisition time can be shortened without decreasing the CR; therefore, it was suggested to improve MR images to avoid motion artifact.

Optimization of T1-weighted Imaging Parameters in MR Carotid Plaque Imaging: Influence for the Quantitative Evaluation among Different MRI Scanner Types.

Carotid artery plaques with high-signal intensity on T1 weighted image (T1 WI) are known to cause cerebral ischemic disease. Signal intensity ratio (SIR), which is calculated from T1 WI in the quantitative evaluation of plaque characterization have been used. However, the various sequences in T1 WI and difference in the sequences were utilized among institutions. Therefore, difference in sequence may influence SIR. The purpose of this study was to evaluate the optimization of T1 WI sequence in MR carotid plaque imaging. We directly compared four kinds of T1 WI imaging techniques, including inversion recovery (IR)-3 dimensional (3D) gradient echo (GRE), 3D fast spin echo (FSE), 2 dimensional (2D) FSE, 2D spin echo (SE), among different magnetic resonance imaging (MRI) scanner. As a result, the 2D SE method had the smallest difference in SIR. Even if 2D SE T1 WI uses a different MRI device, equal SIR is provided. Therefore, 2D SE is appropriate to evaluate the characteristics of carotid plaque.

[Usefulness of short inversion time inversion recovery-low B diffusion weighted imaging after pouring in gadolinium- ethoxybenzyl-diethylene-triaminepentaacetic acid].

Diffusion weighted imaging (DWI) using a low b value for examination of the body is not common, so we examined its usefulness. Phantom experiments were performed in which I changed the length of the echo time (TE), with and without short inversion time inversion recovery (STIR). The signal intensity of each phantom was reduced by using a longer TE or by combination with STIR, but contrast was improved. We noted a similar pattern in clinical cases, and concluded that the results of the phantom study and clinical cases indicated the potential usefulness of TE with moderate STIR. Low-b DWI using appropriate imaging parameters gave better results than high-b DWI followed by visual assessment. The T1 value of normal liver cells is shortened by incorporating gadolinium-ethoxybenzyl-diethylene-triaminepentaacetic acid (Gd-EOB-DTPA). Normal liver cells are close to the null point in STIR-low-b DWI under these conditions. The signal-to-noise ratio (SNR) of normal liver cells thus decreases, unlike that for tumors containing no normal liver cells, giving improved contrast. At high SNRs, the use of low-b DWI provides several advantages: the anatomical location structure is easy to identify, and there is less left lateral division of liver signal degradation. We thus conclude STIR-low-b DWI after injection of Gd-EOB-DTPA to be a useful technique.

[Imaging characteristics of two-dimensional spin echo T1-weighted image in carotid artery plaque].

Recently, T1 weighted image (T1WI) has proven to be useful for diagnosing carotid plaque. This time, the image parameter of two-dimensional spin echo (2D SE) T1WI was examined. Phantoms that imitated muscle and carotid plaque were made. Signal noise ratio (SNR) and the contrast of phantoms were examined when the flip angle (FA) of radio frequency (RF) pulse, repetition time (TR), and echo train length (ETL) was changed. A visual evaluation was done in a clinical case. Both SE and fast spin echo (FSE) SNR improved according to the extension of TR, and the contrast decreased. Moreover, the contrast improved when there was a lot of ETL and the FA of RF pulse. It is thought that this is because SNR and the contrast depend on the interrelation of TR, T1 value, and the FA of RF pulse. When the FA of RF pulse was set to 70 degrees and the TR was set to 400 ms resulting from the phantom experiment, clinical cases obtained great results. This examination confirmed the utility of 2D SE in carotid plaque inspection.

[A study of ADC value in PROPELLER DWI].

Diffusion weighted imaging(DWI)is rapidly becoming widespread in MRI, with many reports of the differential diagnosis using the Apparent Diffusion Coefficient(ADC)being seen. We examined the influence of scan parameter on ADC in PROPELLER-DWI. Neither the TR nor T1 value had a major influence on the ADC value. Number of MPG pulse, effective TE, and T2 value were the factors in which the ADC value was changed. In addition, the ADC value has been changed by the scan sequence. The factor that influenced the ADC value was able to be confirmed by this experiment. It is necessary to understand the influence that an individual factor has on ADC.

[Influence of the difference in start-up echo on signal intensity in the FIESTA sequence].

The FIESTA sequence is a fast imaging method used for various parts in recent years. A constant flip angle (CFA) or linear flip angle (LFA) are used as the start-up echo in many cases. It is reported from CFA, which is the conventional method, that the T1 value and T2 value influence the speed that reaches steady state. However, there is no such report in LFA. Therefore, we examined the influence of the difference of start-up echo method upon signal intensity. In phantoms other than vegetable oil, the difference was not accepted in the change of speed that reaches steady state and the signal intensity in steady-state transit. In LFA, signal intensity of vegetable oil was clearly lower than CFA. The same result was obtained regardless of on or off resonance. From the result, it was thought that it depended on T2/T1 for the speed that reaches steady state. Moreover, the difference in resonant frequency was considered to greatly influence LFA but not CFA. That is, it was suggested by the difference in start-up echo that the signal intensity of fat changes greatly.