Purpose: 67Ga-single photon emission computed tomography (SPECT) images vary according to the imaging time and image display methods. The calculation of an index, such as the standardized uptake value used in positron emission tomography, from 67Ga-SPECT images would enable the accurate evaluation of the region of accumulation. The purpose of this study was to elucidate the conversion formula, the lower detection limit (LDL), and recovery coefficient (RC) for quantifying the radiation concentration in the 67Ga accumulation site. Methods: After chronologically obtaining SPECT/CT images at a radiation concentration of 1.0–442.4 kBq/mL with 27 bottles (diameter: 48 mm, 100 mL), the radiation concentration conversion formula was calculated using the successive approximation reconstruction method. The conversion coefficient was then calculated from the relationship between the count rate and the radiation concentration, and the LDL was determined. To compensate for the partial volume effect, the recovery curve was calculated using the mean SPECT count for six bottles (diameter: 9, 18, 29, 38, 48, and 94 mm). Results: There was a linear relationship between the radiation concentration and the count rate with a good correlation (r=0.99). The LDL was 1.0 kBq/mL. The recovery curve reached a plateau at a diameter of at least 48 mm. Conclusion: The calculation of the absorbed dose index was possible using the radiation concentration conversion formula and the RC.
Diffusion kurtosis imaging (DKI) is a method of analyzing restricted diffusion. Mean kurtosis (MK) is obtained from DKI. It is not known how different MRI scanners and coil systems will change MK when the same imaging parameters are used. The purpose of this study is to identify tendencies in MK when using various MRI scanners and coil systems. A total of 27 healthy volunteers were enrolled in this study. DKI was performed on the brain for each volunteer on five MRI scanner/coil system combinations using the same scan parameters. MK of 10 anatomical areas of the brain were compared, and the signal-noise ratios (SNRs) of b-2000 s/mm2 images were measured in identical areas. There were no significant differences among MKs from multi transmit (MT) MRI systems, but MK was significantly lower on the single transmit MRI system because of pepper artifact caused by low SNR. In conclusion, we found no significant differences in MK among MT systems, and MK was significantly lower without MT.
Three-dimensional fast spin-echo (3D FSE) imaging with variable refocusing flip angle has been recently applied to pre- or post-enhanced T1-weighted imaging. To reduce the acquisition time, this sequence requires higher echo train length (ETL), which potentially causes decreased T1 contrast. Spoiled equilibrium (SpE) pulse consists of a resonant +90° radiofrequency (RF) pulse and is applied at the end of the echo train. This +90° RF pulse brings residual transverse magnetization to the negative longitudinal axis, which makes it possible to increase T1 contrast. The purpose of our present study was to examine factors that influence the effect of spoiled equilibrium pulse and the relationship between T1 contrast improvement and imaging parameters and to understand the characteristics of spoiled equilibrium pulse. Phantom studies were conducted using an magnetic resonance imaging (MRI) phantom made of polyvinyl alcohol gel. To evaluate the effect of spoiled equilibrium pulse with changes in repetition time (TR), ETL, and refocusing flip angle, we measured the signal-to-noise ratio and contrast-to-noise ratio (CNR). The effect of spoiled equilibrium pulse was evaluated by calculating the enhancement rate of CNR. The factors that influence the effect of spoiled equilibrium pulse are TR, ETL, and relaxation time of tissues. Spoiled equilibrium pulse is effective with increasing TR and decreasing ETL. The shorter the T1 value, the better the spoiled equilibrium pulse functions. However, for tissues in which the T1 value is long (>600 ms), at a TR of 600 ms, improvement in T1 contrast by applying spoiled equilibrium pulse cannot be expected.
We aimed to apply the pediatric abdominal CT protocol of Donnelly et al. in the United States to the pediatric abdominal CT-AEC. Examining CT images of 100 children, we found that the sectional area of the hepatic portal region (y) was strongly correlated with the body weight (x) as follows: y=7.14x + 84.39 (correlation coefficient=0.9574). We scanned an elliptical cone phantom that simulates the human body using a pediatric abdominal CT scanning method of Donnelly et al. in, and measured SD values. We further scanned the same phantom under the settings for adult CT-AEC scan and obtained the relationship between the sectional areas (y) and the SD values. Using these results, we obtained the following preset noise factors for CT-AEC at each body weight range: 6.90 at 4.5–8.9 kg, 8.40 at 9.0–17.9 kg, 8.68 at 18.0–26.9 kg, 9.89 at 27.0–35.9 kg, 12.22 at 36.0–45.0 kg, 13.52 at 45.1–70.0 kg, 15.29 at more than 70 kg. From the relation between age, weight and the distance of liver and tuber ischiadicum of 500 children, we obtained the CTDIvol values and DLP values under the scanning protocol of Donnelly et al. Almost all of DRL from these values turned out to be smaller than the DRL data of IAEA and various countries. Thus, by setting the maximum current values of CT-AEC to be the Donnelly et al.’s age-wise current values, and using our weight-wise noise factors, we think we can perform pediatric abdominal CT-AEC scans that are consistent with the same radiation safety and the image quality as those proposed by Donnelly et al.
In external radiotherapy, the X-ray beam passes through the treatment couch, leading to the dose reduction by the attenuation of the couch. As a method to compensate for the reduction, radiation treatment planning systems (RTPS) support virtual couch function, namely “couch modeling method”. In the couch modeling method, the computed tomography (CT) numbers assigned to each structure should be optimized by comparing calculations to measurements for accurate dose calculation. Thus, re-optimization of CT numbers will be required when the dose calculation algorithm or their version changes. The purpose of this study is to evaluate the calculation accuracy of the couch modeling method in different calculation algorithms and their versions. The optimal CT numbers were determined by minimizing the difference between measured transmission factors and calculated ones. When CT numbers optimized by Anisotropic Analytical Algorithm (AAA) Ver. 8.6 were used, the maximum and the mean difference of transmission factor were 5.8% and 1.5%, respectively, for Acuros XB (AXB) Ver. 11.0. However, when CT numbers optimized by AXB Ver. 11.0 were used, they were 2.6% and 0.6%, respectively. The CT numbers for couch structures should be optimized when changing dose calculation algorithms and their versions. From the comparison of the measured transmission to calculation, it was found that the CT numbers had high accuracy.
During percutaneous coronary intervention (PCI) for chronic total occlusion (CTO), longer fluoroscopic time as compared with PCI for non-CTO lesions may cause skin injury by increased radiation. We have performed a multi-center observational study comparing the exposed dose during the PCI of CTO (CTO group) and during the PCI of non-CTO lesions (non-CTO group). Exposure doses were assessed in 313 patients with CTO and 3,310 patients with non-CTO lesions. Total fluoroscopy time (59.0 ±35.5 vs 26.8 ±18.8 min, p<0.0001) and the total air kerma (2.76±2.11 vs 1.27±0.94 Gy, p<0.0001) were significantly greater in the CTO group than in the non-CTO group. The maximum air kerma of the CTO group was 13.62 Gy. Informed consent about the risk of transient depilation and the transient erythema is required for the case with radiation dose over 3 Gy. The frequency of the patient who received radiation >3 Gy was significantly higher in the CTO group as compared with the non-CTO group (34.1% vs 4.9%). Therefore, informed consent before an operation and postoperative follow-up are indispensable for the performed PCI of CTO. Moreover, comprehensive understanding of the exposure dose during operation and to record the final exposure dose may be extremely important for the radiological technologists.
Our aim was to investigate the feasibility of a three-dimensional (3D) -printed head-and-neck (HN) immobilization device by comparing its positional accuracy and dosimetric properties with those of a conventional immobilization device (CID). We prepared a 3D-printed immobilization device (3DID) consisting of a mask and headrest with acrylonitrile-butadiene-styrene resin developed from the computed tomography data obtained by imaging a HN phantom. For comparison, a CID comprising a thermoplastic mask and headrest was prepared using the same HN phantom. We measured the setup error using the ExacTrac X-ray image system. Furthermore, using the ionization chamber and the water-equivalent phantom, we measured the changes in the dose due to the difference in the immobilization device material from the photon of 4 MV and 6 MV. The positional accuracy of the two devices were almost similar in each direction except in the vertical, lateral, and pitch directions (t-test, p<0.0001), and the maximum difference was 1 mm, and 1°. The standard deviations were not statistically different in each direction except in the longitudinal (F-test, p=0.034) and roll directions (F-test, p<0.0001). When the thickness was the same, the dose difference was almost similar at a 50 mm depth. At a 1 mm depth, the 3DID-plate had a 2.9–4.2% lower dose than the CID-plate. This study suggested that the positional accuracy and dosimetric properties of 3DID were almost similar to those of CID.