Development of Upright Computed Tomography With Area Detector for Whole-Body Scans

Abstract

Objectives Multiple human systems are greatly affected by gravity, and many disease symptoms are altered by posture. However, the overall anatomical structure and pathophysiology of the human body while standing has not been thoroughly analyzed due to the limitations of various upright imaging modalities, such as low spatial resolution, low contrast resolution, limited scan range, or long examination time. Recently, we developed an upright computed tomography (CT), which enables whole-torso cross-sectional scanning with 3-dimensional acquisition within 15 seconds. The purpose of this study was to evaluate the performance, workflow efficacy, effects of gravity on a large circulation system and the pelvic floor, and potential clinical impact of upright CT. Materials and Methods We compared noise characteristics, spatial resolution, and CT numbers in a phantom between supine and upright CT. Thirty-two asymptomatic volunteers (48.4 ± 11.5 years) prospectively underwent both CT examinations with the same scanning protocols on the same day. We conducted a questionnaire survey among these volunteers who underwent the upright CT examination to determine their opinions regarding the stability of using the pole throughout the acquisition (closed question), as well as safety and comfortability throughout each examination (both used 5-point scales). The total access time (sum of entry time and exit time) and gravity effects on a large circulation system and the pelvic floor were evaluated using the Wilcoxon signed-rank test and the Mann-Whitney U test. For a large circulation system, the areas of the vena cava and aorta were evaluated at 3 points (superior vena cava or ascending aorta, at the level of the diaphragm, and inferior vena cava or abdominal aorta). For the pelvic floor, distances were evaluated from the bladder neck to the pubococcygeal line and the anorectal junction to the pubococcygeal line. We also examined the usefulness of the upright CT in patients with functional diseases of spondylolisthesis, pelvic floor prolapse, and inguinal hernia. Results Noise characteristics, spatial resolution, and CT numbers on upright CT were comparable to those of supine CT. In the volunteer study, all volunteers answered yes regarding the stability of using the pole, and most reported feeling safe (average rating of 4.2) and comfortable (average rating of 3.8) throughout the upright CT examination. The total access time for the upright CT was significantly reduced by 56% in comparison with that of supine CT (upright: 41 ± 9 seconds vs supine: 91 ± 15 seconds, P < 0.001). In the upright position, the area of superior vena cava was 80% smaller than that of the supine position (upright: 39.9 ± 17.4 mm2 vs supine: 195.4 ± 52.2 mm2, P < 0.001), the area at the level of the diaphragm was similar (upright: 428.3 ± 87.9 mm2 vs supine: 426.1 ± 82.0 mm2, P = 0.866), and the area of inferior vena cava was 37% larger (upright: 346.6 ± 96.9 mm2 vs supine: 252.5 ± 93.1 mm2, P < 0.001), whereas the areas of aortas did not significantly differ among the 3 levels. The bladder neck and anorectal junction significantly descended (9.4 ± 6.0 mm and 8.0 ± 5.6 mm, respectively, both P < 0.001) in the standing position, relative to their levels in the supine position. This tendency of the bladder neck to descend was more prominent in women than in men (12.2 ± 5.2 mm in women vs 6.7 ± 5.6 mm in men, P = 0.006). In 3 patients, upright CT revealed lumbar foraminal stenosis, bladder prolapse, and inguinal hernia; moreover, it clarified the grade or clinical significance of the disease in a manner that was not apparent on conventional CT. Conclusions Upright CT was comparable to supine CT in physical characteristics, and it significantly reduced the access time for examination. Upright CT was useful in clarifying the effect of gravity on the human body: gravity differentially affected the volume and shape of the vena cava, depending on body position. The pelvic floor descended significantly in the standing position, compared with its location in the supine position, and the descent of the bladder neck was more prominent in women than in men. Upright CT could potentially aid in objective diagnosis and determination of the grade or clinical significance of common functional diseases.

Comparison of inspiratory and expiratory lung and lobe volumes among supine, standing, and sitting positions using conventional and upright CT

“…1B) and sitting positions with arms down (Fig. 1C) performed using a 320-detector-row upright CT (prototype TSX-401R, Canon Medical Systems) 2,6 on the same day. Subjects were scanned in the three positions in breath-hold both at the end-inspiration, near total lung capacity on PFT, and at the end-tidal expiration, near functional residual capacity on PFT, as described in a previous study 13 .…”

Evaluation of three-dimensional acromiohumeral distance in the standing position and comparison with its conventional measuring methods

“…This study evaluated the shortest distance between the acromion and humeral head in the standing position by using a newly developed upright CT scanner with a 3D approach. 8,9 Measuring 3D AHD while standing straight was feasible, and the mean value of the 3D AHD of healthy participants without previous injuries was 7.3 mm, ranging from 4.7 mm to 14.0 mm. The AHD was greater in men than in women.…”

“…The minimum distance between the acromion and humeral head in the standing position has not been evaluated using a 3D approach. However, a novel upright CT scanner has been developed, which enables 3D whole-torso cross-sectional scanning in the standing position 8 and evaluation of the effect of gravity on the human body. 9 This study aimed to clarify the 3D minimum distance between the acromion and humeral head of normal shoulders in the standing position using an upright CT scanner and compare the AHD values with those obtained using conventional methods.…”

Comparisons of acromiohumeral distance measurements between two- and three-dimensional imaging and between the supine and standing positions

“…This study used imaging from a newly developed upright CT scanner [8,9] to accurately measure AHD in the standing position, which is better representative of daily living than is AHD measured when supine.…”

“…Moreover, it is possible that the AHD could change between the supine and standing positions owing to the effect of gravity and the rotation of the upper arm. This study aimed to accurately measure the distance between the acromion and the humeral head in the standing position using a newly developed upright CT scanner [8,9] and to evaluate differences in measurements of the AHD between the supine and standing positions and between 2D and 3D imaging.…”