Signal intensity changes in anterior cruciate ligament autografts: relation to magnetic field orientation

RATIONALE AND OBJECTIVES

The purpose of this study was to use magnetic resonance (MR) imaging to investigate the contribution of graft alignment to changes in signal intensity in anterior cruciate ligament (ACL) autografts.

MATERIALS AND METHODS

Forty patients who had undergone reconstruction of the ACL with an autograft underwent MR examinations of the knee in extension and flexion. The signal intensity of the intratibial bone tunnel and intraarticular portions of ACL graft were measured, and signal intensity ratios were defined by dividing the mean signal intensity of the graft by the mean signal intensity of the fatty marrow. The angles from the intraarticular and intratibial bone tunnel portions of the graft to the static magnetic field were measured for each signal intensity ratio. The Hotteling T2 test was used to evaluate the differences in signal intensity ratios to the differences in angles from flexion to extension for the intratibial bone tunnel and intraarticular portions of the graft.

RESULTS

Significant increases occurred in the signal intensity of the graft and the angle with the change in position from flexion to extension for both the intratibial bone tunnel (P < .01) and intraarticular (P < .01) portions of the graft. Changes in signal intensity ratios were greater than zero, and these values differed significantly for the intraarticular and the intratibial bone tunnel (P < .01) portions of the graft.

CONCLUSION

The signal intensity changes of the ACL graft related to changes in its alignment are likely a result of the magic-angle effect.

Two-dimensional aortographic coronary arteriography with above-K-edge monochromatic synchrotron radiation

RATIONALE AND OBJECTIVES

The diagnostic potential of two-dimensional aortographic coronary arteriography with synchrotron radiation was examined in dogs.

METHODS

The experiment was performed at a wiggler beam line by using a silicon monocrystal, fluorescent plate, and avalanche-type camera. The x-ray energy was adjusted to just above the iodine K-edge to obtain the highest contrast. Quantitative densitometry was used to compare intravenous coronary arteriography with aortographic coronary arteriography.

RESULTS

Aortographic coronary arteriography clearly depicted the branches of the coronary arteries such as the left anterior descending coronary artery, circumferential coronary artery, and right coronary artery to sizes of less than 0.2 mm without major overlap of coronary arteries. Intravenous coronary arteriography depicted only the branches of the left anterior descending coronary artery and right coronary artery with poor image quality. The ratio of contrast material dilution was about 2.4 to 3.4 in aortographic procedures, whereas in intravenous procedures it ranged widely from 7.7 to 15.6.

CONCLUSION

These preliminary investigations indicate that two-dimensional aortographic coronary arteriography with synchrotron radiation promises to be a minimally invasive and easily repeatable method of clearly imaging the coronary arteries.

Hyperattenuating rim on noncontrast CT of the liver: probable peritumoral sparing of fatty infiltration

CT scans showing a hyperattenuating rim within the liver were retrospectively evaluated in 10 patients to clarify the character, aetiology and clinical significance. All patients had hepatic tumours (7 cavernous haemangiomas in 6 patients, 3 metastatic tumours and 1 hepatocellular carcinoma) as well as fatty infiltration of the liver. Typical features of the hyperattenuating rim on noncontrast CT of the liver included (1) attenuation similar to that of the spleen, (2) a circular or semicircular shape, (3) a width of a few millimeters, (4) peritumoral localization and (5) loss of visualization with contrast enhancement. No such rims were noted around hepatic tumours unassociated with fatty infiltration. Peritumoral sparing of fatty infiltration was inferred. A hyperattenuating rim on noncontrast liver CT, although rare, suggests the presence of a hepatic tumour in fatty liver.

[The efficacy of early 123I-MIBG scintigraphy for pheochromocytoma diagnosis]

Early scintigraphy, that obtained 6 hours after intravenous administration of a low dose of 123I-metaiodobenzylguanidine (111 MBq) was evaluated for diagnostic efficacy. The accumulation of 123I-MIBG in the tumor masses of nine patients with pheochromocytoma and one patient with cortical adenoma were noted. The smallest pheochromocytoma visualized was 3 cm in diameter. The hepatic uptake of this radiolabeled compound was helpful to understand the anatomical position of the abnormal uptake. Three of five postoperative cases of pheochromocytoma showed uptake in the metastasis in the skeleton or recurrences in the neck or contralateral adrenal gland. No ectopic pheochromocytoma was found in the pelvic cavity. Faint accumulation in the normal medulla was noted in 45% of the cases. The present results demonstrate that superior images can be obtained in scintigrams takes 6 hours after administration of a lower dose of 123I-MIBG.