Development of a subject-standing-type cone-beam computed tomography for chest and orthopedic imaging.

A subject-standing-type cone-beam computed tomography (CT) with high spatial resolution has been developed as a new three-dimensional imaging modality for subjects standing or sitting naturally on a turntable. A 16-in. X-ray image intensifier and charge coupled device camera acquires a 12-bit 5122-pixel projection at 60 f/s and the rotation period is 4.8 or 9.6 s for 288 or 576 projections, respectively. To reduce image noise, the system controls the X-ray pulse duration and iris-opening area through real-time analysis of the projection image. To improve CT accuracy and eliminate artifacts, the veiling glare of the image intensifier and scattered X-rays are corrected. Human chest and orthopedic studies with about 50 patients were conducted. Three-dimensional images with a spherical field of view with a diameter of 21-25 cm, 0.4- to 0.5-mm voxels and a 512(3) matrix were obtained. In coronal, sagittal and volume rendering images, the surface of arthrosis was visualized smoothly with a resolution higher than that of conventional CT. In the case of gonarthrosis, narrowing of the clearance at the surface of arthrosis was visualized clearly under body-weight burdening, which would be difficult if the subject was lying down.

[Evaluation of parathyroid imaging methods with 99mTc-MIBI--the comparison of planar images obtained using a pinhole collimator and a parallel-hole collimator].

Parathyroid scintigraphy with 99mTc-MIBI was performed using two kinds of collimators, namely, a pinhole one and a parallel-hole one, to evaluate which one was more suitable for the detection of hyperfunctioning parathyroid lesions. In the studies using 99mTc source, the pinhole collimator showed better efficiency and spatial resolution in the distance where the parathyroid scan are actually performed. In the phantom study, the nodular activities modeling parathyroid lesions were visualized better on the images obtained using the pinhole collimator. In clinical studies for 30 patients suspicious of hyperparathyroidism, hyperfunctioning parathyroid nodules were better detected when the pinhole collimator was used. In conclusion, the pinhole collimator was thought to be more suitable for parathyroid scintigraphy with 99mTc-MIBI than the parallel-hole collimator.

[Evaluation of renal function using 99mTc-MAG3 comparison with 131I-OIH by simultaneous dual energy peak acquisition method].

A newly developed 99mTc-labeled renal scintigraphic and renographic agent, 99mTc-mercaptoacetyltriglycine (99mTc-MAG3) was studied clinically and compared with 131I-OIH in 16 patients with various renal and urinary tract disorders. The abdominal aorta and the common iliac artery were clearly visualized in the vascular phase. The renogram patterns showed the same pattern in all cases. The parameters on the renogram such as Tmax, T2/3, T1/2 were compared. The highly significant correlations of Tmax, T2/3 and T1/2 were observed between 99mTc-MAG3 and 131I-OIH with correlation coefficient of 0.982, 0.907, 0.990, respectively. In all cases, excretion of 99mTc-MAG3 was slower than that of 131I-OIH and the ratios of Tmax, T2/3 and T1/2 between 99mTc-MAG3 and 131I-OIH were 1.113 +/- 0.121, 1.277 +/- 0.247, 1.179 +/- 0.075, respectively. It is concluded that 99mTc-MAG3 is useful renal imaging agent as an alternative to 131I or 123I-OIH.

[Phase I clinical study of 99mTc-ECD].

A phase I clinical study of 99mTc-L,L-ethyl cysteinate dimer (99mTc-ECD) was carried out in 3 normal volunteers. There was no significant change in vital signs and laboratory parameters attributing to the radiopharmaceutical. 99mTc-ECD was rapidly taken up by the brain, reaching the maximum peak activity within 1 min after the injection and remained relatively constant over several hours. The brain uptake of 99mTc-ECD at 5 min was 5.4 +/- 0.5% which decreased to 5.0 +/- 0.3% by 65 min. 99mTc-ECD cleared rapidly from other organs. The primary excretion route was through the kidneys. Cumulative 99mTc activity in the urine at 90 min and 24 hr were 60.2 +/- 7.3% and 88.5 +/- 10.3%, respectively. The critical organ was the bladder wall with an estimated radiation dose of 0.073 mGy/MBq, which was acceptable value. Clear SPECT images were obtained at 30, 90 and 150 min postinjection. In conclusion, 99mTc-ECD is a safe and promising radiopharmaceutical for the evaluation of regional cerebral blood flow.

[Phase I clinical study on 99mTc-MIBI].

A phase I clinical study on 99mTc-hexakis 2-methoxy isobutylisonitrile (99mTc-MIBI) was carried out in 6 normal volunteers. There was no significant change in vital signs and laboratory parameters attributing to the reagent other than complaint of slight and transient metallic taste immediately after the injection in 4 volunteers. The highest dosimetry was calculated as 1.1 mGy/37 MBq at lower large intestine, which was within the acceptable range. 99mTc-MIBI was rapidly cleared from the blood and accumulated in the heart immediately after the injection with 1.4% dose and 1.8% dose at 5 min at rest and at stress, respectively. The retention of radioactivity in the heart well continued for at least several hours. The heart-to-lung ratio was over 2.00 at 5 min and heart-to-liver ratio was over 1.00 at 60 min. Myocardial planar and SPECT images were obtained with high quality. In conclusion, 99mTc-MIBI is a useful myocardial perfusion imaging agent.

[Tumor imaging using 99mTc-hexamethylpropyleneamine oxime].

Tumor imagings have been performed in 32 tumor sites in 28 patients with a variety of malignancies by using 99mTc-HM-PAO. They have been compared with radionuclide angiography and conventional tumor imagings such as 67Ga citrate or 201TlCl scanning, and then their possible values have been evaluated for the investigation of tumor blood flow. Tumors were clearly visualized in 19 out of 32 sites, with 59% of positive rate. Good correlation was observed between the radioactivity in the tumor site on static image of 99mTc-HM-PAO and the radioactivity at arterial phase on radionuclide angiography, which represents tumor blood flow. The radioactivities in the marginal regions tended to be stronger than those in the center of large tumors. These results indicated that tumor imaging by 99mTc-HM-PAO mainly reflected tumor blood flow. On the other hand, 99MTc-HM-PAO imagings were not well correlated with 67Ga-studies, while they were coincided with all 201Tl scannings performed. It suggested that the affinity of 99mTc-HM-PAO to capillary wall also involved in its accumulation in the tumor. In conclusion, tumor imaging by 99MTc-HM-PAO was able to estimate tumor blood flow, and this examination would be helpful for the management of malignancies.

[Renography and renal imaging with 123I-orthoiodohippurate; comparison with 131I-orthoiodohippurate].

Renography and renal imaging with 123I-orthoiodohippurate (OIH) were performed in 29 patients with various renal diseases, and a comparison made with 131I-OIH. In all patients, renograms and images with 123I-OIH were superior to those with 131I-OIH, because of the increased density and image excellence of 123I-OIH. In addition, dynamic images to evaluate renal blood flow, as well as high quality sequential excretion images, can be obtained with 123I-OIH. From our clinical results, 123I-OIH is expected to replace 131I-OIH in renal function studies.

Assessment of mucociliary clearance in patients with tracheobronchoplasty using radioaerosol.

To assess mucociliary clearance in patients with tracheobronchoplasty, radioaerosol inhalation scanning was performed in 14 patients. The unilateral total lung clearance curve was fitted into two compartmental curves, fast and slow, by least-squares techniques in order to assess mucociliary clearance of the bronchial tree quantitatively. Half-time (T 1/2) of the curve resulting from the subtraction of the slow compartment curve from the fast compartment curve was calculated. The mucociliary clearance of the bronchial tree post so-called lobectomy (N = 5) was intact (T 1/2; 13.1 +/- 7.3 min). On the other hand, the mucociliary clearance of the bronchial tree postreconstruction (N = 14) was prolonged (T 1/2; 28.3 +/- 10.6 min), compared with that of the control bronchial tree (N = 15, T 1/2; 11.9 +/- 3.9 min) (p less than 0.01). However, the mucociliary clearance of the bronchial tree postreconstruction showed improvement with the passage of time, and the original clearance was regained 5 to 12 mo after the operation. Radioaerosol inhalation studies revealed both the degree of impairment and the recovery time of mucociliary clearance in patients post-tracheobronchoplasty.