Verification of the effect of data-driven brain motion correction on PET imaging.

INTRODUCTION: Brain positron emission tomography/computed tomography (PET/CT) scans are useful for identifying the cause of dementia by evaluating glucose metabolism in the brain with F-18-fluorodeoxyglucose or Aß deposition with F-18-florbetaben. However, since imaging time ranges from 10 to 30 minutes, movements during the examination might result in image artifacts, which interfere with diagnosis. To solve this problem, data-driven brain motion correction (DDBMC) techniques are capable of performing motion corrected reconstruction using highly accurate motion estimates with high temporal resolution. In this study, we investigated the effectiveness of DDBMC techniques on PET/CT images using a Hoffman phantom, involving continuous rotational and tilting motion, each expanded up to approximately 20 degrees. MATERIALS AND METHODS: Listmode imaging was performed using a Hoffman phantom that reproduced rotational and tilting motions of the head. Brain motion correction processing was performed on the obtained data. Reconstructed images with and without brain motion correction processing were compared. Visual evaluations by a nuclear medicine specialist and quantitative parameters of images with correction and reference still images were compared. RESULTS: Normalized Mean Squared Error (NMSE) results demonstrated the effectiveness of DDBMC in compensating for rotational and tilting motions during PET imaging. In Cases 1 and 2 involving rotational motion, NMSE decreased from 0.15-0.2 to approximately 0.01 with DDBMC, indicating a substantial reduction in differences from the reference image across various brain regions. In the Structural Similarity Index (SSIM), DDBMC improved it to above 0.96 Contrast assessment revealed notable improvements with DDBMC. In continuous rotational motion, % contrast increased from 42.4% to 73.5%, In tilting motion, % contrast increased from 52.3% to 64.5%, eliminating significant differences from the static reference image. These findings underscore the efficacy of DDBMC in enhancing image contrast and minimizing motion induced variations across different motion scenarios. CONCLUSIONS: DDBMC processing can effectively compensate for continuous rotational and tilting motion of the head during PET, with motion angles of approximately 20 degrees. However, a significant limitation of this study is the exclusive validation of the proposed method using a Hoffman phantom; its applicability to the human brain has not been investigated. Further research involving human subjects is necessary to assess the generalizability and reliability of the presented motion correction technique in real clinical scenarios.

[Relative Error between Organ Doses and Size-specific Dose Estimates for a Specific Location When the Mean CTDIvol Value Is Used for Calculation].

Size-specific dose estimates (SSDEs) are dose indices that account for differences in body shape in computed tomography (CT) scans, allowing the evaluation of approximate absorbed doses in any cross section that could not be obtained with the volume CT dose index (CTDIvol). When using automatic exposure control (AEC), CTDIvol is modulated in the body axis direction, but the value displayed after the examination is the mean CTDIvol for the entire scan, and it is expected that the SSDE value will change depending on which value is used in the calculation. In this study, using a human body phantom, we examined the influence of whether the mean CTDIvol or the modulation value for each slice is used to calculate the SSDE on local organ dose evaluation. A program to calculate water equivalent diameter according to the procedure in the American Association of Physicists in Medicine Report No. 220 was developed and compared. As a result, SSDE calculated using the mean CTDIvol (local-SSDEmean) overestimated organ doses in the lung region by 18%-56% compared with those calculated by a web system for evaluating CT exposure doses (WAZA-ARIv2, Japan). In contrast, local-SSDEmodulated, which was calculated using the modulated value of the CTDIvol, was able to estimate the organ dose with a relative error of 10%-13%. The average local-SSDE over the entire body axis direction was not significantly different between the two methods, regardless of which method was used for CTDIvol. If the mean CTDIvol is stored in the Digital Imaging and Communications in Medicine (DICOM) header tag (0018, 9345) of the CT image and the modulated CTDIvol value is not available for each slice, the calculated local SSDE will contain many errors and will not correctly reflect the organ doses at the scan region. In such cases, it is available to use the method of evaluating local organ doses by multiplying the SSDE, which is the average of the SSDE for the entire scan, by a factor for each organ.

Improvement of Imaging Conditions to Improve the Detection Rate of Head and Neck Cancer by Positron Emission Tomography/Computed Tomography Examination.

Positron emission tomography (PET)/computed tomography (CT) has improved sensitivity and resolution using silicon photomultiplier as a photosensor. Previously, only a fixed setting was available for the shooting time of 1 bed, but now, the shooting time can be changed for each bed. Time can be shortened or extended depending on the target area. A few studies reported on image reconstruction conditions for head and neck cancer in whole-body PET/CT examinations. Thus, this study aimed to optimize the imaging conditions of the head and neck region during whole-body imaging. A cylindrical acrylic container with a 200 mm diameter was used to simulate the head and neck area using a PET/CT system equipped with a semiconductor detector. Spheres of 6-30 mm in diameter were enclosed in the 200 mm diameter cylindrical acrylic vessel. Radioactivity in 18F solution (Hot:BG ratio 4:1) was enclosed in a phantom following the Japanese Society of Nuclear Medicine (JSNM) guidelines. Background radioactivity concentration was 2.53 kBq/mL. List mode acquisition of 1,800 s was collected at 60-1,800 s with the field of view of 700 mm and 350 mm. The image was reconstructed by resizing the matrix to 128 × 128, 192 × 192, 256 × 256, and 384 × 384, respectively. The imaging time per bed in the head and neck should be at least 180 s, and the reconstruction conditions should be a field of view (FOV) of 350 mm, matrix sizes of ≥ 192, and a Bayesian penalized likelihood (BPL) reconstruction with a ß-value of 200. This allows detection of > 70% of the 8-mm spheres in the images.

Image quality and radiation dose of low-tube-voltage CT with reduced contrast media for right adrenal vein imaging.

OBJECTIVES: To compare image quality and radiation dose of right adrenal vein (RAV) imaging computed tomography (CT) among conventional, low kV, and low kV with reduced contrast medium protocols. METHODS: One-hundred-and-twenty patients undergoing adrenal CT were randomly assigned to one of three protocols: contrast dose of 600mgI/kg at 120-kV tube voltage setting (600-120 group), 600mgI/kg at 80kV (600-80 group), and 360mgI/kg at 80kV (360-80 group). Iterative reconstruction was used for 80-kV groups. Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) of the RAV and size-specific dose estimates (SSDE) were measured. Three radiologists evaluated 4-point visualisation scores of RAV by consensus reading. RESULTS: The RAV detectability was 95%, 97.2%, and 97.3% for 600-120, 600-80, and 360-80 groups, respectively (p=1.000). Visualisation scores were not significantly different among the groups (p=0.152). There were no significant differences in CNR or SNR between the 600-120 and 360-80 groups. SSDE of the 360-80 group was significantly lower than that of the 600-120 group (5.86mGy±1.44 vs. 7.27mGy±1.81, p<0.001). CONCLUSIONS: 80-kV scans with 360 mgI/kg contrast media showed comparable detectability of RAV to conventional scans, while reducing 19% of SSDE.