CyberKnife® provides continuous guidance through radiography, allowing instantaneous X-ray images to be obtained; it is also equipped with 6D adjustment for patient setup. Its disadvantage is that registration is carried out just before irradiation, making it impossible to perform stereo-radiography during irradiation. In addition, patient movement cannot be detected during irradiation. In this study, we describe a new registration system that we term “Machine Vision,” which subjects the patient to no additional radiation exposure for registration purposes, can be set up promptly, and allows real-time registration during irradiation. Our technique offers distinct advantages over CyberKnife by enabling a safer and more precise mode of treatment. “Machine Vision,” which we have designed and fabricated, is an automatic registration system that employs three charge coupled device cameras oriented in different directions that allow us to obtain a characteristic depiction of the shape of both sides of the fetal fissure and external ears in a human head phantom. We examined the degree of precision of this registration system and concluded it to be suitable as an alternative method of registration without radiation exposure when displacement is less than 1.0 mm in radiotherapy. It has potential for application to CyberKnife in clinical treatment.
The purpose of this study was to evaluate the detection performance of simulated nodules in chest computed tomography (CT) images and nuclear medicine images with an ordinary liquid crystal display (LCD) and a medical LCD (grayscale standard display function: GSDF) and gamma 2.2. We collected 72 chest CT image slices obtained from an LSCT phantom with simulated signals composed of various sizes and CT values and 78 slices of monochrome and color nuclear medicine images obtained from a digital phantom with a simulated signal composed of various sizes and radiation levels. Six observers performed receiver operating characteristic (ROC) analysis using a continuous scale. The area under the ROC curve (AUC) was calculated for each monitor. The average AUC values for detection of chest CT images on a medical LCD (GSDF), medical LCD (gamma 2.2), and ordinary LCD were 0.71, 0.67, and 0.73, respectively. The average AUC values for detection of monochrome nuclear medicine images using a medical LCD (GSDF), medical LCD (gamma 2.2), and ordinary LCD were 0.81, 0.75, and 0.72, respectively. The average AUC values for detection of color nuclear medicine images on a medical LCD (GSDF), medical LCD (gamma 2.2), and ordinary LCD were 0.88, 0.86, and 0.90, respectively. Observer performance for detection of simulated nodules in chest CT images and nuclear medicine images was not significantly different between the three LCD monitors. We therefore conclude that an ordinary LCD monitor can be used to detect simulated nodules in chest CT images and nuclear medicine images.
Volumetric modulated arc therapy (VMAT) is an irradiation method in which the multi-leaf collimator (MLC) shape, gantry speed and dose-rate is continuously varied. Gantry speed and dose-rate are treated as specific dynamic parameters (DPs) in VMAT, so there is a need to confirm the influence of DPs on dose distribution. The purpose of this study was to verify the impact of DPs on the accuracy of dose delivery in VMAT. We adopted an irradiation scenario in which DPs were modified from the original plan without making any changes in the dose distribution. We carried out irradiation and measured the dose distributions using a Delta4 diode array phantom, during which we acquired log files that enabled us to calculate DPs. The results showed that dose errors exceeding 1% or geometric errors greater than 1 mm were not produced by modifying the DPs. We were therefore able to verify the impact of DPs on dose delivery accuracy in VMAT.
Purpose: In the iterative reconstruction method, image noise tends to increase in proportion to falling available photon count and increasing update number. Image filtering is an important factor in single photon emission computed tomography (SPECT) image reconstruction, but it is frequently treated in a subjective way. The aim of this study was to evaluate the effects of pre-reconstruction filtering and post-reconstruction filtering on the iterative reconstruction process. Methods: Using simulation phantoms, projection data were reconstructed using ordered subsets expectation maximization (OSEM) with or without compensation for resolution recovery. Pre- and post-reconstruction filtering was performed using a Butterworth filter (BW) (range: 0.3–1.3 cycles/cm) and a Gaussian filter (GA) (range: 0.3–1.3 mm) with various parameters. We evaluated the variances of full width at half maximum (FWHM), coefficients of variation (CV), image contrast and normalized mean squared error (NMSE) values. Results: The FWHM values for pre-reconstruction filtering tended to be lower than those observed for post-reconstruction filtering. These values were 5.1 mm (pre-reconstruction) and 6.7 mm (post-reconstruction). The CV on pre- and post-reconstruction filtering was 7.5% and 11.6%. Pre-reconstruction filtering reduced image noise more effectively than post-reconstruction filtering. The contrast for pre-reconstruction filtering was similar to that observed after post-reconstruction filtering. However, contrast after filtering with a GA slowly decreased as compared to the BW. NMSE values obtained by pre-reconstruction filtering tended to be lower than those observed for post-reconstruction filtering. Conclusions: Pre-reconstruction filtering provided SPECT image quality comparable to that from post-reconstruction filtering, especially when using the BW. Our results suggest that pre-reconstruction filtering is a beneficial method when applied to the iterative reconstruction method with or without compensation for resolution recovery.
The purpose of this study was to evaluate the relationship of body habitus, blood glucose level and injected dose, respectively, with BGO (Bi4Ge3O12) positron emission tomography (PET) image quality using commercially available 2-deoxy-2-[18F] fluoro-D-glucose (FDG). We also evaluated the relationship between PET image quality and acquisition time for each weight group. Method: One hundred twenty-five patients (66 male, 59 female) were enrolled in the study. We adopted liver signal-to-noise ratio (liver SNR) as an image quality index, derived from the region of interest (ROI) placed on the axial image of the liver. Results: The correlation coefficient between liver SNR and dose per weight was 0.502. The liver SNR indicated a negative relationship with body weight, body mass index (BMI) and cross sectional area of the patient’s body, with the correlation coefficients of −0.594, −0.479 and −0.522, respectively. For all weight groups, an extended acquisition time of at least 60 s/bed was necessary to improve liver SNR. Conclusion: The findings of this study are potentially of use for designing imaging protocols for the BGO-PET/CT system when using commercially available FDG. It is easy to obtain good image quality for patients of low to average body size with the standard injection dose. However, large patients should be injected, wherever possible, with an FDG dose of up to 5 MBq/kg. The acquisition time in overweight and obese patients should be as longer as possible than in standard weight patients.
The array spatial sensitivity encoding technique (ASSET) is a form of parallel imaging (PI). Another scan, called a reference scan (Ref) is required before acquiring the ASSET image. However, artifacts tend to interfere with recognition of the object due to differences between the ASSET scan and Ref. scan. This is because the liver is in contact with the diaphragm, making it susceptible to respiratory motion. Further, since the liver upper edge is surrounded by the lung field, there is a risk of susceptibility artifacts. The purpose of this study was to reduce the accompanied deployment failure artifact using a thick slice sensitivity map. Our data showed it was possible to reduce accompanied deployment failure artifacts, as well as to suppress noise, by increasing the slice thickness of the Ref scan.
In this study we analyzed the influence of region of interest (ROI) selection on the uptake ratio of the liver to the liver plus heart at 15 min (LHL15) during 99mTc-galactosyl human serum albumin (GSA) scintigraphy and determined the optimal ROI by evaluating the individual effects of different ROIs in the heart on LHL15. Twenty patients were randomly selected from those who had undergone 99mTc-GSA scintigraphy GSA between April 2008 and June 2009. The liver body (L/B) ratio, liver uptake 15 min (LU15), and LHL15 were analyzed and compared among the following ROIs: entire heart, both ventricles, right ventricle, and left ventricle. There were significant differences in the L/B ratio and LU15 values among the different ROIs. However, LHL15 showed a tendency to shift toward a normal value when the size of the ROI was small (only the right or left ventricle), resulting in a lack of distinction between normal and abnormal LHL15 values. Furthermore, setting the entire heart as the ROI was difficult and reproducibility was low. Our results suggest that the use of both ventricles as the ROI provides optimal LHL15 values during 99mTc-GSA scintigraphy.
Alongside current improvements in the performance of computer tomography (CT) systems, there has been an increase in the use of bolus tracking (BT) to acquire arterial dominant phase images for dynamic CT at optimal timing for characterization of liver focal lesions. However, optimal BT settings have not been established. In the present study, methods of contrast enhancement and BT setting values were evaluated using a multicenter post-marketing surveillance study on contrast media used in patients with chronic hepatitis and/or cirrhosis who had undergone liver dynamic CT for diagnosis of hepatocellular carcinoma, conducted by Daiichi Sankyo Co., Ltd. The results suggested the contrast injection method to be clinically useful if the amount of iodine per kilogram of body weight is set at 600 mg/kg and the injection duration at 30 s. To achieve a good arterial dominant scan under conditions where the injection duration is fixed at 30 s or the average injection duration is 34 s using the fixed injection rate method, the scan delay time should ideally to be set to longer than 13 s. If using the BT method, we recommend that the BT settings should be revalidated in reference to our results.
In recent years, dose justification and optimization have been attempted in percutaneous coronary intervention (PCI); however, deterministic effects have been reported. To prevent radiation skin injuries in PCI, it is necessary to measure the patient entrance skin dose (ESD), but an accurate dose measurement method has not yet been established. In this study, we developed a dosimetry gown that can measure the ESD during PCI using multiple radiophotoluminescence dosimeters (RPLDs). The RPLDs were placed into 84 pockets that were sewn into a dosimetry gown. Patients wear the original dosimetry gown during the procedures, after which we obtain accurate ESD measurements. We believe that this method using RPLDs and a newly-designed dosimetry gown provides accurate ESD measurements during PCI. We expect this system to become a standard method for measuring ESD during PCI.