A new method for assessing lung tumor motion in radiotherapy using dynamic chest radiography.

Dynamic chest radiography (DCR) is a recent advanced modality to acquire dynamic and functional images. We developed a new method using DCR and the free analysis software, Kinovea, to assess lung tumor motion. This study aimed to demonstrate the usefulness of our method. Phantom and clinical studies were performed. In the phantom study, dynamic images of a moving lead sphere were acquired using DCR, and the motion of the phantom was tracked using Kinovea in a DCR video. The amplitude of phantom motion was measured and compared with a predetermined baseline amplitude. In a clinical study, DCR and respiratory-gated four-dimensional computed tomography (4D-CT) were performed on 15 patients who underwent stereotactic body radiation therapy for lung tumors. The amplitudes of tumor motion in DCR and 4D-CT were measured in the superior-inferior (SI), left-right (LR), and anterior-posterior (AP) directions, and the square root of the sum of squares (SRSS) of the amplitude was calculated in all directions. Spearman's rank correlation and the Wilcoxon signed-rank test were performed to determine the correlations of the amplitudes of tumor motion obtained using DCR and 4D-CT. In the phantom study, the absolute mean error between the measured and predetermined amplitudes was 0.60 mm (range: 0.061.53 mm). In the clinical study, the amplitudes of tumor motion obtained using DCR correlated significantly with those of 4D-CT in the SI and LR directions, as did the SRSS values. The median amplitudes for DCR were significantly higher than those for 4D-CT in all (SI, LR, and AP) directions, as were the SRSS values. Our proposed method based on DCR and Kinovea is useful for assessing lung tumor motion, visually and quantitatively. Therefore, DCR has potential as a new modality for evaluating lung tumor motion in radiotherapy.

[Analysis of accidents for magnetically induced displacement of the large ferromagnetic material in magnetic resonance systems].

To improve magnetic resonance (MR) safety, we surveyed the accidents caused by large ferromagnetic materials brought into MR systems accidentally. We sent a questionnaire to 700 Japanese medical institutions and received 405 valid responses (58%). A total of 97 accidents in 77 institutions were observed and we analyzed them regarding incidental rate, the detail situation and environmental factors. The mean accident rate of each institute was 0.7/100,000 examinations, which was widely distributed (0-25.6/100,000) depending on the institute. In this survey, relatively small institutes with less than 500 beds tend to have these accidents more frequently (p<0.01). The institutes in which daily MR examination counts are more than 10 patients have fewer accidents than those with less than 10 daily examinations. The institutes with 6-10 MR examinations daily have significantly more accidents than that with more than 10 daily MR examinations (p<0.01). The main mental factors of the accidents were considered to be "prejudice" and "carelessness" but some advocate "ignorance." Though we could not find significant reduction in the institutes that have lectures and training for MR safety, we should continue lectures and training for MR safety to reduce accidents due to "ignorance."

AUTOMATIC ACQUISITION OF CT RADIATION DOSE DATA: USING THE DIAGNOSTIC REFERENCE LEVEL FOR RADIATION DOSE OPTIMIZATION.

The present work describes that we try to construct a system that collects dose information that performed CT examination from multiple facilities and unified management. The results of analysis are compared with other National diagnostic reference level (DRL), and the results are fed back to each facility and the cause of the abnormal value is investigated for dose optimization. Medical information collected 139 144 tests from 33 CT devices in 13 facilities. Although the DRL of this study is lower than that of Japan DRL, it was higher than the DRL of each country. When collecting all the examination, it is thought that the variation of the dose due to the error other than the intended imaging site is large. In future, we should continue to collect information in order to DRL renewal and we also think that it is desirable to collect information on physique and detailed scan region as well.

[Fundamental study of the relation between flow velocity and signal intensity in the TrueFISP sequence].

The purpose of this study was to evaluate the effect of inflow phenomenon on TrueFISP. We created a phantom using a vinyl tube and distilled water, and applied a pump-oxygenator to the phantom to obtain stationary flow. First, to evaluate the effect of inflow and the dephase phenomenon on signal intensity, the phantom was measured for the signal intensity of variable flow velocity. Second, the relation of TR/TE with signal intensity was analyzed. The results showed that a flow velocity of less than 15 cm/sec did not participate in signal reduction; however, signal intensity was reduced when flow velocity was more than 30 cm/sec. Moreover, the reduction of signal intensity was remarkable with a flow velocity of 50-100 cm/sec, which corresponds with arterial flow velocity. In the analysis of TR/TE, signal intensity was increased when TR of less than 5 ms was applied to the slow velocity of 15 cm/sec. Signal intensity was decreased when the same TR was applied to the high velocity of 50-100 cm/sec. When TR was 6-9 ms, peak signal intensity was recognized at the high velocity of 50-100 cm/sec. This peak, however, might correspond only to the inflow phenomenon, and steady state might have already collapsed. Based on these results, we concluded that TrueFISP is suitable for the imaging of slow flow velocity. A short TR of less than 5 ms was effective for obtaining high signal intensity. Our next goal will be to apply TrueFISP to MR venography, although further investigation will be necessary.

[Usefulness of 3D-VIBE method in breast dynamic MRI: imaging parameters and contrasting effects].

MR imaging (MRI) has been reported to be a useful modality to characterize breast tumors and to evaluate disease extent. Contrast-enhanced dynamic MRI, in particular, allows breast lesions to be characterized with high sensitivity and specificity. Our study was designed to develop three-dimensional volumetric interpolated breath-hold examination (3D-VIBE) techniques for the evaluation of breast tumors. First, agarose/Gd-DTPA phantoms with various concentrations of Gd-DTPA were imaged using 3D-VIBE and turbo spin echo (TSE). Second, one of the phantoms was imaged with 3D-VIBE using different flip angles. Finally, water excitation (WE) and a chemical shift-selective (CHESS) pulse were applied to the images. Each image was analyzed for signal intensity, signal-to-noise ratio (1.25*Ms/Mb) (SNR), and contrast ratio [(Ms1-Ms2)/[(Ms1+Ms2)/2]]. The results showed that 3D-VIBE provided better contrast ratios with a linear fit than TSE, although 3D-VIBE showed a lower SNR. To reach the best contrast ratio, the optimized flip angle was found to be 30 degrees for contrast-enhanced dynamic study. Both WE and CHESS pulses were reliable for obtaining fat-suppressed images. In conclusion, the 3D-VIBE technique can image the entire breast area with high resolution and provide better contrast than TSE. Our phantom study suggests that optimized 3D-VIBE may be useful for the assessment of breast tumors.

[Evaluation of metal artifact in computed radiography].

We know that computed radiography (CR) has many factors to generate artifacts, such as the over / under shoot, aliasing and more. Recently, we encountered an artifact, we call a metal artifact, not attributable to any known factors in clinical images. To elucidate the cause of this artifact, we did some experiments with an in-house phantom. The experiments showed that the metal artifact was seen only when we put an object that absorbs X-rays parallel to the scanning line on imaging plate (IP). From these results, we speculated that the factor causing the afterglow is associated with photo-stimulated luminescence from IP.

[T2 image contrast evaluation using three dimension sampling perfection with application optimized contrasts using different flip angle evolution (3D-SPACE)].

PURPOSE: Sampling perfection with application optimized contrasts using different flip angle evolution (3D-SPACE) sequence enables one to decrease specific absorption rate (SAR) by using variable flip angle refocusing pulse. Therefore, it is expected that the contrast obtained with 3D-SPACE sequences is different from that of spin echo (SE) images and turbo spin echo (TSE) images. The purpose of this study was to evaluate the characteristics of the signal intensity and central nervous system (CNS) image contrast in T(2) weighted 3D-SPACE. METHOD: Using 3 different sequences (SE, 3D-TSE and 3D-SPACE) with TR/TE=3500/70, 90 and 115 ms, we obtained T(2) weighted magnetic resonance (MR) images of inhouse phantom and five healthy volunteers' brain. Signal intensity of the phantom which contains various T(1) and T(2) value was evaluated. Tissue contrasts of white/gray matter, cerebrospinal fluid (CSF)/subcutaneous fat and gray matter/subcutaneous fat were evaluated for a clinical image study. RESULTS: The phantom study showed that signal intensity in 3D-SPACE significantly decreased under a T(1) value of 250 ms. It was markedly decreased in comparison to other sequences, as effective echo time (TE) was extended. White/gray matter contrast of 3D-SPACE was the highest in all sequences. On the other hand, CSF/fat and gray matter/fat contrast of 3D-SPACE was higher than TSE but lower than SE. CONCLUSION: CNS image contrasts of 3D-SPACE were comparable to that of SE. Signal intensity had decreased in the range where T(1) and T(2) values were extremely short.

[An investigative report concerning safety and management in the magnetic resonance environment: there are more accidents than expected].

Using a questionnaire, we surveyed 2,500 facilities in Japan to clarify medical accidents concerning the magnetic resonance device and its environment. Data derived from 1,319 valid responses (52.8%), allowed us to analyze the situation of (or the reason for) the occurrence of the accidents and their environmental factors. Five hundred and nine facilities (39% of all facilities) had the experience of magnetically induced displacement of the large ferromagnetic material. Intravenous (I.V.) drip stands were involved the largest number of them: 31% (228 cases). Oxygen bottles had the second largest number of incidents: 20%. There were also many incidents involving various materials brought in by non-medical staff (e.g. stepladder for construction). About 20% of the accidents occurred outside of working hours. Patients in 12% of the facilities (154 facilities) experienced burns. In 39 of the cases, burns were received to the inside of the thighs. In 38 of the cases, patients received burns from an electrical cable touching the skin. There were also frequent incidents of burning regarding the boa. We received reports of burns and pain from the halo vest even though it's required to be worn for MR safety. Regarding incidents of contraindications, 280 patients with pacemakers were brought into the magnetic resonance (MR) inspection room. Twelve percent of the facilities experienced natural quench. Lack of training for the staff who introduce and operate high magnetic field devices are considered involving frequently occurring accidents of attractions and burns at hospitals with over 500 beds caused by carrying in materials.