Circulation time end points. A quantitative comparison of saccharin and radioiodinated albumin as indicators

The optimization of scan timing for contrast-enhanced magnetic resonance angiography

OBJECTIVE

To determine the optimal scan timing for contrast-enhanced magnetic resonance angiography and to evaluate a new timing method based on the arteriovenous circulation time.

MATERIALS AND METHODS

Eighty-nine contrast-enhanced magnetic resonance angiographic examinations were performed mainly in the extremities. A 1.5T scanner with a 3-D turbo-FLASH sequence was used, and during each study, two consecutive arterial phases and one venous phase were acquired. Scan delay time was calculated from the time-intensity curve by the traditional (n = 48) and/or the new (n = 41) method. This latter was based on arteriovenous circulation time rather than peak arterial enhancement time, as used in the traditional method. The numbers of first-phase images showing a properly enhanced arterial phase were compared between the two methods.

RESULTS

Mean scan delay time was 5.4 sec longer with the new method than with the traditional. Properly enhanced first-phase images were found in 65% of cases (31/48) using the traditional timing method, and 95% (39/41) using the new method. When cases in which there was mismatch between the target vessel and the time-intensity curve acquisition site are excluded, erroneous acquisition occurred in seven cases with the traditional method, but in none with the new method.

CONCLUSION

The calculation of scan delay time on the basis of arteriovenous circulation time provides better timing for arterial phase acquisition than the traditional method.

Aortoiliac and lower extremity arteries: comparison of three-dimensional dynamic contrast-enhanced subtraction MR angiography and conventional angiography

PURPOSE

To determine the clinical feasibility of three-dimensional dynamic contrast agent-enhanced subtraction magnetic resonance (MR) angiography in patients with symptoms of lower extremity ischemia.

MATERIALS AND METHODS

Twenty-three patients suspected of having lower extremity ischemia underwent three-dimensional dynamic contrast-enhanced subtraction MR angiography of the aortoiliac arteries and arteries of the lower extremity. As the reference standard, conventional angiography was also performed. For data analysis, the arterial system was divided into 10 segments. Each segment was classified as normal, mildly stenosed, moderately stenosed, severely stenosed, or occluded.

RESULTS

At conventional angiography, 83 stenosed segments (14 mildly stenosed, 16 moderately stenosed, 14 severely stenosed, and 39 occluded) were identified in a total of 423 segments. For the segments with more than mild stenosis, MR angiography was 97.1% sensitive and 99.2% specific.

CONCLUSION

Three-dimensional dynamic contrast-enhanced subtraction MR angiography has high sensitivity and specificity. This technique is a noninvasive alternative to conventional angiography for screening patients suspected of having lower extremity ischemia.