Purpose: Sensitivity and count rate performance of the latest PET/CT scanners with a silicon photomultiplier (SiPM) have been substantially improved compared to scanners with a photomultiplier tube (PMT), thereby promising a low-dose whole-body PET scan with maintaining image quality. However, it is ethically difficult to verify the low-dose protocol in actual clinical settings. In this study, we investigated the effect of dose reduction on reconstructed images by using a low-dose simulation technique, i.e., reducing the number of events from the acquired data. Method: For 21 subjects who underwent whole-body ¹⁸F-FDG PET examination with an SiPM-based PET/CT scanner, Biograph Vision (Siemens Healthineers, Erlangen, Germany), at a dosage of 3.5 MBq/kg and a continuous bed motion speed of 1.1 mm/sec (the standard protocol in our hospital), the number of events in acquired list data (100%; “full-dose”) was reduced to 50%, 25%, 12.5%, and 6.25% (“low-dose”). The low-dose reconstructed images were evaluated visually and physically with reference to the full-dose images. The physical evaluation was performed by calculating differences in SUV_max at abnormal uptake (n=54) between the full-dose and low-dose images. Result: The 25% data images were visually acceptable, and the difference in SUV_max between the 100% and 25% data images was 9.8±13.5%. Conclusion: Our results suggest that Biograph Vision is a feasible method to reduce conventional dose with the potential use of 25% data images.

Purpose: Radioproteomics studies investigating the relationship between lesion phenotype and proteins have been progressed. The purpose of this study was to develop a radioproteomics method for discriminating between active and inactive immune checkpoint molecules based on lesion phenotype. Methods: From the public database TCGA-BRCA, mRNA and fat suppression contrast-enhanced T₁-weighted images of 49 patients with breast cancer were selected for the experiment. Using mRNA, we defined cases with active (10 cases) and inactive (39 cases) immune checkpoint molecules. To discriminate these cases using lesion phenotype, 275 radiomics features were measured from the tumor area. After selecting 3 radiomics features by using Lasso, logistic regression was employed to discriminate between active and inactive cases of immune checkpoint molecules. Results: Evaluation of ROC analysis showed that the AUC was 0.81. Conclusion: Patients whose immune cell function is being braked by immune checkpoint molecules are likely to respond to immune checkpoint inhibitors when their activity is inhibited. Therefore, our results may be applied to predict the effects of immune checkpoint inhibitors in breast cancer treatment.

Purpose: The noise power spectrum (NPS) in computed tomography (CT) images potentially varies with the X-ray tube angle in a spiral orbit of the helical scan. The purpose of this study was to propose a method for measuring the NPS for each angle of the X-ray tube. Methods: Images of the water phantom were acquired using a helical scan. As a conventional method, we measured the two-dimensional (2D) NPS from each image and averaged them; the obtained 2D-NPS was referred to as NPS_conventional. In the proposed method, we made the X-ray tube angle θ (0°≤θ<360°) to correspond to the image according to each slice position of the images that located within the travel distance of the CT scan table per 360° rotation of the X-ray tube. We obtained the 2D-NPS from each image and assigned the θ (0°, 30°, 60°, 90°, 120°, 150°, 180°); the obtained 2D-NPS was referred to as NPSs_θ. The NPSs_θ was compared to the NPS_conventional. Also, we investigated the dependency of the NPSs_θ on the θ. Results: The NPS_conventional was found to be isotropic, and in contrast, the NPSs_θ was anisotropic. The NPSs_θ showed a continuously rotational change while increasing the θ. There was an excellent correlation (R²>0.999) between the rotation angle of NPS_θ and the θ. Conclusion: The proposed method was demonstrated to be effective for evaluating anisotropic noise characteristics depending on the X-ray tube angle.

Purpose: Although breast compression has been an efficient practice to reduce the breast dose in mammography, there may be some differences between analog and digital systems. The purpose of this study was to evaluate the dose-reduction efficiency by breast compression in digital mammography under its own criterion that signal difference-to-noise ratio (SDNR) be kept at a certain value. Method: By adopting SDNR as an image quality indicator and average glandular dose (AGD) as a dose indicator, we measured SDNR versus AGD relationship for each breast depth. Then by utilizing figure of merit (FOM), we calculated the breast depth that we had to reduce for halving the breast dose while keeping the SDNR. Result: To halve the dose, 1.49 cm compression was necessary for 0% breast density, 1.25 cm for 50%, and 1.06 cm for 100%. Conclusion: Through FOM analysis, we quantitatively revealed the dose-reduction efficiency by breast compression in digital mammography.

Purpose: To investigate whether the volume of white matter hyperintensity (WMH) extracted from FLAIR images changes when the imaging parameters of the original images are changed. Methods: Seven healthy volunteers were imaged by changing the imaging parameter ETL of FLAIR images, and WMHs were extracted and their volumes were calculated by the automatic extraction software. The results were statistically analyzed to examine the relationship (Experiment 1). Simulated images with different SNRs were created by adding white noise to four examples of healthy volunteer images. The SNR of the simulated images simulated the SNR of the measured images of different ETLs. The WMH was extracted from the simulated images and its volume was calculated using the automatic extraction software (Experiment 2). Results: Experiment 1 showed that there was no significant difference between FLAIR imaging parameters and WMH volume in automatic white matter signal analysis, except for some conditions. Experiment 2 showed that as the SNR of the original image decreased, the volume of high white matter signal extracted decreased. Conclusion: In automatic white matter signal analysis, WMH was shown to be small when the ETL of the FLAIR sequence was larger than normal and/or the SNR of the image was low.

Purpose: In order to prevent magnetic materials from being brought into the magnetic resonance imaging (MRI) examination room, many facilities have metal detectors, etc., but there are various types of equipment with different performance and characteristics. The purpose of this study was to evaluate each detector in actual clinical practice. Methods: At multiple facilities, gate-type magnetic detectors, pole-type magnetic detectors, handy-type magnetic detectors, and handy-type metal detectors were used to identify 9 types of objects that may be brought into the MRI examination room. We performed evaluation of detection distance measurement assuming actual operation. Results: The gate type was only able to detect objects with strong magnetism. With the pole type, the closer the measurement distance was to the pole, the more objects could be detected, and the lower the pole, the shorter the detection distance. With the handy type, there were many objects that could be detected when the device and the object were brought into close contact. Conclusion: The detectability of the instruments varied depending on the size and type of the object. It is important to understand the characteristics of each device and use it according to the purpose in carrying-in confirmation before the examination.