This study proposes a method to accurately estimate the phantom scatter factor (Sp) of arbitrary rectangular fields. We measured output doses in water and air; these measured values were based on square fields and a limited number of symmetric rectangular fields using 4 MV and 10 MV X-rays of a Varian Clinac-iX. We calculated Sp from these measured values. Then, using these Sp values, we estimated equations of Sp on square fields consisting of the primary dose, Day’s scatter, and forward scatter. This equation may be used to estimate the Sp value on a square field, but it cannot estimate the Sp value on a rectangular field. We investigated the calculation method for an equivalent square of a rectangular field. As a result, this study’s calculation method for an equivalent square, the area ratio correction method, was more accurate than the conventional Bjärngard’s method. Therefore, when using the approximate equation of Sp on a square field and the equivalent square calculated by the area ratio correction method, a Sp value of an arbitrary rectangular field may be accurately estimated.
Development of multi-detector row computed tomography (MDCT) has enabled three-dimensions (3D) scanning with minute voxels. Minute voxels improve spatial resolution of CT images. At the same time, however, they increase image noise. Multi-planar reconstruction (MPR) is one of effective 3D-image processing techniques. The conventional MPR technique can adjust slice thickness of MPR images. When a thick slice is used, the image noise is decreased. In this case, however, spatial resolution is deteriorated. In order to deal with this trade-off problem, we have developed the weighted-averaging multi-planar reconstruction (W-MPR) technique to control the balance between the spatial resolution and noise. The weighted-average is determined by the Gaussian-type weighting function. In this study, we compared the performance of W-MPR with that of conventional simple-addition-averaging MPR. As a result, we could confirm that W-MPR can decrease the image noise without significant deterioration of spatial resolution. W-MPR can adjust freely the weight for each slice by changing the shape of the weighting function. Therefore, W-MPR can allow us to select a proper balance of spatial resolution and noise and at the same time produce suitable MPR images for observation of targeted anatomical structures.
The opposite-type array coil is useful because it is easy to attach in magnetic resonance imaging (MRI) examinations away from the center area. It is not well understood that sensitivity characteristics change when coil elements shift. We studied the effect when both coil elements (17×14 cm) shifted to the opposite side; we examined a hand including the wrist. The signal-to-noise ratio (SNR) of the axial image by the subtraction map declined 2.6%/cm. The profile of the sagittal and coronal view by the SNR map shows that the greater the distance between the center of the upper and lower coil elements, the lower the SNR is on the center of the examination area and the higher the SNR is on the edge of the examination area. In removing 10 cm from each of the coil elements, the profile became wide and linear. In the case of removing more than 7.5 cm, the wide area of uniformity was shown in the center of the images of sensitivity distribution. Uniformity by the segment method increased more than 10 cm. Use of the opposite-type array coil when shifting both coil elements to the opposite side may extend the examination area.
Background: The image qualities of coronary 64-multidetector-row computed tomography angiography (CCTA) in patients with atrial fibrillation (Afib) are often not enough. This study clarifies how to use electrocardiogram (ECG) -editing in Afib. Methods: We performed CCTA (Aquilion 64 with beam pitch: 0.125, 0.35 s/r) in 33 patients (M/F=24/9, age: 71±9 yr, mean heart rate: 71±12 bpm) with Afib. We injected 5 mg of verapamil into the vein when the mean HR was ≥80 bpm. First, we reconstructed images after deleting short RR (<800, 750, 700, 650, or 600). Second, we reconstructed images in 4 different methods: (1) end-systolic images with Phase Navi (automatically selecting an optimal phase) (ES-Navi), (2) Mid-diastolic images with Phase Navi (MD-Navi), (3) Mid-diastolic images reconstructed by the “R+absolute time method” [Edit-MD (R+)], and (4) Mid-diastolic images reconstructed by the “R-absolute time method” [Edit-MD (R–)]. We reconstructed 1 and 2 without ECG-editing, and 3 and 4 were reconstructed after ECG-editing without a data deficit. The quality of the images was classified into 3 ranks: no artifact (3), mild artifact (2), and severe artifact (1). Results: The image quality point of CCTA, reconstructed after deleting RR<750, was similar to RR<800, and RR<750 was even higher than that after deleting HR<600, 650, or 700. The mean image quality point of CCTA that was reconstructed by Edit-MD (R–) or Edit-MD (R+) was significantly higher than ES-Navi or MD-Navi. Conclusion: The high image quality of CCTA could be reconstructed after deleting RR<750 in 76% or after deleting RR<800 in 70% of Afib. The reconstruction using Edit-MD (R–) or Edit-MD (R+) without a data deficit could provide a better quality CCTA than using PhaseNavi in Afib.
We evaluated exposed-radiation doses on dual-source cardiac computed tomography (CT) examinations with prospective electrocardiogram (ECG)-gated fast dual spiral scans. After placing dosimeters at locations corresponding to each of the thoracic organs, prospective ECG-gated fast dual spirals and retrospective ECG-gated dual spiral scans were performed to measure the absorbed dose of each organ. In the prospective ECG-gated fast dual spiral scans, the average absorbed doses were 5.03 mGy for the breast, 9.96 mGy for the heart, 6.60 mGy for the lung, 6.48 mGy for the bone marrow, 9.73 mGy for the thymus, and 4.58 mGy for the skin. These values were about 5% of the absorbed doses for the retrospective ECG-gated dual spiral scan. However, the absorbed dose differed greatly at each scan, especially in the external organs such as the breast. For effective and safe use of the prospective ECG-gated fast dual spiral scan, it is necessary to understand these characteristics sufficiently.
We studied the position dependent influence that sensitivity correction processing gave the signal-to-noise ratio (SNR) measurement of parallel imaging (PI). Sensitivity correction processing that referred to the sensitivity distribution of the body coil improved regional uniformity more than the sensitivity uniformity correction filter with a fixed correction factor. In addition, the position dependent influence to give the SNR measurement in PI was different from the sensitivity correction processing. Therefore, if we divide SNR of the sensitivity correction processing image by SNR of the original image in each pixel and calculate SNR ratio, we can show the position dependent influence that sensitivity correction processing gives the SNR measurement in PI. It is with an index of the sensitivity correction processing precision.
Magnetic resonance spectroscopy (MRS) is a useful tool for obtaining metabolic information non-invasively. However, low reducibility of MRS data, measuring biases caused by the operator, effects of relaxation time, and environmental contamination may sometimes become problematic. In this study, we examined contamination in echo time (TE) and the availability of outer volume suppression (OVS) by using the excitation and localization methods. In addition, we investigated the optimized condition for three-dimensions (3D)-chemical shift imaging (CSI) in gliomas. Contamination was dependent on resolution in the excitation and localization methods and on CSI resolution, but it was not dependent on TE. The additional installation of OVS and saturation pulse (SAT) corresponding to the target sites were extremely useful. There was concern about the influence of chemical shift, crosstalk, contamination, and no radio frequency (RF) uniformity in the marginal volume of interest (VOI). Metabolite distribution was deteriorated along the Z-axis but not in the X–Y plane. It, however, was improved by using a small voxel size in the Z-axis.
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.
We compared the accuracy in evaluating an unrapture aneurysm between NV and 3D-DSA. In vitro, we evaluated the accuracy in calculating the volume of the Aneurysm model. We compared the diameter of the first coil and estimated the diameter of the Aneurysm. The Aneurysm size calculated by NV resembled the first coil more than the size measured by 3D-DSA. In clinical cases, the measurement of NV is objective; the measurement of 3D-DSA, however, is subjective by person. NV has an automatic measurement that is useful for clinical cases.
Changing into slippers when entering the nuclear medicine management district prevented pollution expansion. Accidents involving patients falling occurred in university facilities. It was thought that changing slippers was the cause. The pollution situation was measured in three facilities by using the smear method and the direct technique to examine the effect of changing slippers. The current state was measured. After pollution prevention guidance was continuously done, pollution expansion was measured; three weeks of measurements were compared. Pollution was detected in the first period of weeks at a frequency of 19 times. For the latter period, it was detected 6 times. Half the pollution was in the restroom. Pollution was reduced by doing pollution prevention guidance for the restroom. Patients’ falls occur even if they change slippers. Falling accidents can be decreased.
Objectives: We have designed a phantom to evaluate acquisition and reconstruction parameters using contrast transfer function (CTF). The goal of this study was to evaluate the accuracy of the phantom for contrast resolution. Methods: The phantom consisted of spaced (0–14 mm, 1 mm intervals) pairs of cubic containers (5 mm wide, 20 mm long, and 50 mm high). The phantom’s accuracy was examined by comparing a real value of a measured count profile using the phantom with a theoretical value obtained by the line spread function (LSF) using a line source. A SPECT acquisition was 256×256 matrix (pixel size: 0.9×0.9 mm2), 360 degrees at 30 s/view. The radius of rotation was set to 15 cm, and the types of collimators were low energy high resolution (LEHR) and low middle energy general purpose (LMEGP). Reconstructions were performed with filtered backprojection and ordered subsets expectation maximization method (10 iterations, 10 subsets) with collimator-detector response correction. Results: The actual measured count profile and CTF accorded closely with the theoretical one. Discussion: The line pair (LP) phantom, obtained with smaller pixels, was really accurate. The size of cubic containers poses as a minimal problem for accurately evaluating the contrast resolution and plotted counts profile. Conclusions: This phantom could be a useful method for evaluating acquisition and reconstruction parameters in SPECT.