Diffusion-weighted imaging (DWI) has been used to characterize not only the brain, but also the breast by implementation of faster imaging techniques and higher magnetic field strengths. However, the optimum b value, which is an important scan parameter for DW images contrast on 3 T breast magnetic resonance imaging (MRI) has not been established. The purpose of this study was to investigate the influence of different b value combinations on the image contrast and apparent diffusion coefficient (ADC) in patients with known invasive carcinoma, ductal carcinoma in situ (DCIS), and normal mammary gland in breast DWI. The analysis procedure consisted of the following methods: 1) T2 correction of DW images with echo-planar imaging (EPI) T2-weighted images; 2) contrast measurement between normal mammary gland and tumor tissues; 3) ADC measurement of normal mammary gland and tumor tissues. In many cases, the highest contrast between normal mammary gland and tumor tissues was obtained using a b value of 1500 s/mm2. Our results indicated that when only one b value is used, the b value in which signal intensities of normal mammary gland decreases down to noise level, and the contrast between normal mammary gland and tumor tissues is recommended. ADC value decreased with increasing b value. Therefore, when determining the ADC threshold level, it is important to perform the evaluation using ADC values calculated from DW images with the same b value in clinical studies.
The purpose of this study was to design and construct a phantom for using motion artifact in the electrocardiogram (ECG)-gated reconstruction image. In addition, the temporal resolution under various conditions was estimated. A stepping motor was used to move the phantom over an arc in a reciprocating manner. The program for controlling the stepping motor permitted the stationary period and the heart rate to be adjusted as desired. Images of the phantom were obtained using a 320-row area-detector computed tomography (ADCT) system under various conditions using the ECG-gated reconstruction method. For estimation, the reconstruction phase was continuously changed and the motion artifacts were quantitatively assessed. The temporal resolution was calculated from the number of motion-free images. Changes in the temporal resolution according to heart rate, rotation time, the number of reconstruction segments and acquisition position in z-axis were also investigated. The measured temporal resolution of ECG-gated half reconstruction is 180 ms, which is in good agreement with the nominal temporal resolution of 175 ms. The measured temporal resolution of ECG-gated segmental reconstruction is in good agreement with the nominal temporal resolution in most cases. The estimated temporal resolution improved to approach the nominal temporal resolution as the number of reconstruction segments was increased. Temporal resolution in changing acquisition position is equal. This study shows that we could design a new phantom for estimating temporal resolution.
Objective: This research compared the field of view with the tissue absorbed dose and effective doses using the two dental cone beam computed tomography (CBCT) scanners. Materials and Methods: Two CBCT devices, an Alphard VEGA and 3DX multi-image micro CT MCT-1, were used. Measurements were made using an Alderson RANDO phantom and thermoluminescence dosimeters (TLDs). The calculation of the effective dose was carried out according to ICRP Publication 60 and 103. Results: The effective doses for Alphard VEGA D mode, I mode, P mode, and C mode were 86, 238, 413, and 323 μSv, respectively. The effective doses using 3DX for the maxillary incisor, maxillary molar, mandibular incisor, mandibular molar, TMJ, and mandibular molar scout images were 27, 30, 48, 60, 14, and 1 μSv, respectively. Conclusions: Both Alphard VEGA and 3DX values revealed salivary gland and oral mucosa doses much higher than those required for other tissues. It is necessary to select a small mode suitable in order to realize optimization.
The aim of this study was to assess the exposure dose value (DLP) displayed on the operator console in a computed tomography system with automatic exposure control (CT-AEC) which decides the exposure dose from a positioning image. We measured exposure dose with two kinds of CT systems and evaluated the error of the displayed DLP value on the operator console against the measured DLP value. The assessment was performed in three sites: head and neck, upper chest, and lower abdomen. As a result, the errors of displayed value with CT-AEC against the error without CT-AEC in system A (4.09%) were significantly different on two assessment sites (head and neck: –4.02%, upper chest: 6.60%). There is no significant difference on the third assessment site (lower abdomen: 0.06%). On the other hand, those values in system B (8.38%) were almost similar with no significant differences (head and neck: –1.12%, upper chest: –1.85%, lower abdomen: –0.64%). The results show that there were significant differences noted between the errors of displayed value with CT-AEC and without CT-AEC in system A for the head and neck and the upper chest. In conclusion, displayed value with CT-AEC and without CT-AEC were about the same error. However, the possibility that the error depended on a model and the examination site of CT was shown.
Dynamic magnetic resonance (MR) imaging for pituitary microadenomas is usually performed in 2-dimensional (2D) multi-slice method which used coronal T1-weighted imaging with turbo spin echo (SE) method. However, on MR images using 2D multi-slice method, the detectability of small lesions between slices may decrease. Therefore, the aim of our study is to investigate the influence that imaging parameters give to T1-weighted image with 3-dimensional (3D) turbo SE method, and to examine the use of 3D turbo SE method as the detection of pituitary microadenomas. We can plan the shortening of imaging time by shortening repetition time (TR), because the contrast to noise ratio (CNR) in the 3D turbo SE method was superior enough than that of the 2D turbo SE method. In addition, low refocusing flip angle induced the decrease of CNR, but it has the effect which decreases flow-induced artifacts. Dynamic MR imaging which used coronal T1-weighted imaging with 3D turbo SE method is feasible by utilizing the reduction of TR and low refocusing flip angle, as well as the combination of parallel imaging and radial sampling.
There are several methods for measuring modulation transfer function (MTF) in computed tomography (CT) images. The aluminum slit method, scanning a phantom consisting of a thin aluminum foil sandwiched by flat plastic slabs, is a standard method for measuring field of view (FOV) in clinical CT scan. But this method requires extreme caution when handling metal foil of high precision. Therefore, we devised a more simple method named air gap slit (AS) method. This new technique is based on the aluminum slit method but use air gap instead of metal foil between phantoms. The MTF was calculated from a reversed profile curve of air slit which indicated minimum CT number. The aim of this study was to investigate a possibility of AS method evaluating MTF. We investigated fluctuation of MTF and FOV in clinical CT scan compared with the aluminum slit method. The result showed that the fluctuation of MTF was caused by statistics noise and is more affected by a bone kernel than standard kernel when reconstructing. Also, the MTF value in AS method was slightly higher than in aluminum slit method and did not correspond with. AS method is a useful method for measurement of MTF in clinical CT scan. When we use this method, we have to take into consideration the noise influence of data.
In interventional X-ray for cardiology of flat panel digital detector (FPD), the phenomenon that exposure dose was suddenly increased when a subject thickness was thickened was recognized. At that time, variable metal built-in filters in FPD were all off. Therefore, we examined whether dose reduction was possible without affecting a clinical image using metal filter (filter) which we have been conventionally using for dose reduction. About 45% dose reduction was achieved when we measured an exposure dose at 30 cm of acrylic thickness in the presence of a filter. In addition, we measured signal to noise ratio/contrast to noise ratio/a resolution limit by the visual evaluation, and there was no influence by filter usage. In the clinical examination, visual evaluation of image quality of coronary angiography (40 cases) using a 5-point evaluation scale by a physician was performed. As a result, filter usage did not influence the image quality (p=NS). Therefore, reduction of sudden increase of exposure dose was achieved without influencing an image quality by adding filter to FPD.
The immobilization device for treatment becomes important to obtain fixation and reproducibility of the treatment position. It was confirmed that reproducibility of the treatment position obtains higher accuracy by the method of using immobilization device. Methods: We divided into three terms by the methods of immobilization. An infrared reflective marker performs the setup of a position at the start of treatment, and setup of the patient in a fixed implement is performed by ExacTrac. Difference between coordinates of the immobilization device and the patient position was calculated by the vector in three directions. We estimated the position error index (PEindex) by using the square root of the sum of square of each vectors, and evaluated the amount of differences of patient position at three terms. Results: Mean and standard deviation of index values were 9.53±7.21, 8.50±5.93, and 6.42±3.80 at each three terms. With every passing year, the amount of gap and difference of the patient fixation has decreased. Conclusion: By the improvement of the use of the immobilization device, gap and difference of fixation has decreased. Accordingly, we could obtain better accuracy of fixation.
The management of the radiation dose is very important in interventional radiology (IVR), especially in percutaneous coronary intervention (PCI). Therefore, we measured entrance surface doses at the interventional reference point of 27 cardiac intervention procedures in 22 cardiac catheterization laboratories around Hiroshima, and compared these doses. Recently, for cardiac interventional radiology, the X-ray machines using flat-panel detectors (FPD) instead of image intensifiers (I.I.) is increasing; 13 systems used FPD and 14 systems used I.I. For fluoroscopy rate, the difference between laboratories was 9 times. For cineangiography rate, the difference between laboratories was 7 times. In addition, between both devices, the I.I. group is bigger than the FPD group. When comparing by the same condition, for the dose at the interventional reference point, no significant difference was detected between the FPD group and the I.I. group. This study shows that FPD is not available for reducing the radiation dose simply. Therefore, it is necessary that we think of the balance with image quality and radiation dose. The optimization of the devices and cardiac intervention procedures becomes very important.
Determination of the input function for the 99mTc-ethyl cysteinate dimmer brain uptake ratio (99mTc-ECD BUR) method as a non-invasive quantitative measurement of cerebral blood flow measurement is of critical importance in order to improve the accuracy of this method. The input functions were experimentally obtained by setting the regions of interest (ROIs) in the ascending aorta, aortic arch, and descending aorta on the 49 chest RI-angio images. rCBFs by the BUR method with 3 input functions of the 6 cases were compared with those by the 123I-iodoamphetamine (IMP) continuous arterial blood sampling method in order to determine the best location for the ROI of the input function. The input function of the ascending aorta was higher than those of the aortic arch and the descending aorta. The input functions of the aortic arch and the descending aorta decreased due to the origin of the three branches of the right brachiocephalic artery, left subclavian artery, and left common carotid artery. A good correlation was found in the regional cerebral blood flow (rCBF) values between the 123I-IMP continuous arterial blood sampling method and the 99mTc-ECD BUR method with the input function of the ascending aorta. Therefore, the ascending aorta is the best location for the ROI of the input function for the 99mTc-ECD BUR method.
We tried to remove contamination of radioisotope (RI) for an X-ray detector (photostimulable phosphor plate; IP) and verified that our procedure suggested by Nishihara et al. was effective for decontamination. The procedure was as follows. First, the IP was kept for approximately twelve hours, and then it was processed [image (A)] as well as a clinical processing mode. Second, using a wet-type chemical wiper, we scavenged the IP to remove the adhered RI on its surface. Then, once again, the IP was kept for approximately fifteen hours and processed [image (B)] in order to check an effect of decontamination. Finally, the two images of (A) and (B) were analyzed using ImageJ, which can be downloaded as a free software, and a percentage of removal was calculated. The procedure was applied to two IPs using the FCR 5501 plus. In the present case, the percentage of removal was approximately 96%. The removed radioisotopes in the chemical wipers were analyzed by Ge detector. Then, 134Cs and 137Cs were found with activities of 2.9 4.3 Bq and 3.5 5.2 Bq, respectively. For three months after that, we cannot see black spots on the IPs owing to the contamination of the RI and there are no defects caused by decontamination using a wet-type chemical wiper.
In our institute, an MR apparatus, MAGNETOM VISION (Siemens) was replaced by ECHELON Vega (HITACHI). Z-score data acquired by MPRAGE (VISION) was compared with those by radio frequency-spoiled steady-state acquisition with rewinded gradient echo (RSSG) and gradient echo inversion recovery (GEIR) (ECHELON). For this study, ten normal volunteers were recruited and their data ware obtained within two months using both apparatuses. In addition, the difference of the contrasts of the images of these apparatuses was compared. There was a significant difference between Z-scores of MPRAGE and RSSG while there was no difference between MPRAGE and GEIR. As for the contrast, data of MPRAGE were similar to those of GEIR. To compare Z-scores acquired with MAGNTOM VISION (Siemens), it seems appropriate to use GEIR in ECHELON Vega.
Purpose: The aim of this study is to investigate various intra-fractional errors and to determine the appropriate planning target volume (PTV) margins in intensity modulated radiation therapy (IMRT) for prostate cancer. Methods: Ten patients with prostate cancer treated with IMRT between July 2009 and March 2010 were analyzed. PTV was created by adding 4 mm posterior and 7 mm anterior and lateral margins to the clinical target volume (CTV) including prostate and proximal seminal vesicles. Intra-fractional set-up and organ motion errors were measured using cone beam computed tomography (CBCT) images before and after each irradiation. Systematic and random errors were calculated by van Herk and Stroom’s models. Results: Intra-fractional errors of set-up and organ motion were 0.70±0.84 mm and 0.88±0.95 mm in the left-right (L-R), 1.04±0.98 mm and 1.69±1.58 mm in the cranial-coudal (C-C), and 1.08±1.01 mm and 1.91±1.58 mm in the anterior-posterior (A-P) directions, respectively. The errors in the C-C and A-P were significantly larger than those in the L-R (p<0.01). The organ motion errors in the C-C and A-P were significantly larger than the set-up errors (p<0.01). The appropriate PTV margin estimated in this study was 4.73 mm. Conclusions: Intra-fractional errors in all directions were less than 2 mm and required PTV margin in the study was similar to actual posterior margin in our routine practice. It is important to determine intra-fractional errors as well as inter-fractional errors to deliver successful IMRT for prostate cancers.
The objective of this study was to develop a personal computer-based nuclear medicine data processor for education and research in the field of nuclear medicine. We call this software package “Prominence Processor” (PP). Windows of Microsoft Corporation was used as the operating system of this PP, which have 1024×768 image resolution and various 63 applications classified into 6 groups. The accuracy was examined for a lot of applications of the PP. For example, in the FBP reconstruction application, there was visually no difference in the image quality as a result of comparing two SPECT images obtained from the PP and GMS-5500A (Toshiba). Moreover, Normalized MSE between both images showed 0.0003. Therefore the high processing accuracy of the FBP reconstruction application was proven as well as other applications. The PP can be used in an arbitrary place if the software package is installed in note PC. Therefore the PP is used to lecture and to practice on an educational site and used for the purpose of the research of the radiological technologist on a clinical site etc. widely now.
In order to obtain an image of scattered X-ray in the diagnosis domain, we have newly developed a pin-hole camera. Because of the necessity of the X-ray shielding, the pin-hole part has a depth corresponding to that of the shielded material. As a result, efficiencies of obliquely incident X-rays are reduced. To decrease the descent of the efficiencies, we developed a large camera using a 10×12 inch size phosphor plate as an X-ray detector. A phantom was irradiated by X-rays with conditions of 500 mAs and 5000 mAs, and images of scattered X-rays were obtained. The former image showed scattered X-rays from the phantom. The latter image showed those from the air of beam axis as well as from the phantom. Moreover, we made a new proposal to obtain an optical image using the fading effect.