Application Of 3.0T Time-Resolved Magnetic Resonance Angiography In Patients With Peripheral Arterial Occlusive Disease

Part one Functional evaluation of calf arteries in PAOD patients with 3.0 T TWIST MRAObjective:1. To verify the necessity of using TWIST MRA in calf artery.2. To explore the correlation between information derived from TWIST MRA and ankle-brachial index (ABI). Materials and Methods:34 patients with confirmed or suspected peripheral arterial occlusive disease (PAOD) received TWIST MRA of the calf station. Siemens 3.0T MRI was used. 0.1 ml/kg Gadolinium contrast agents was used at TWIST MRA. TWIST MRA data were used to determine the bolus arriving time of the popliteal artery, bolus arriving time of the pedal veins, and peak enhancement time of middle anterior tibial artery, middle posterior tibial artery and middle peroneal artery. Further calculations were conducted to acquire the time difference of the bolus arrival in the popliteal artery between the two legs, calf artery transit time (the popliteal artery-pedal vein transit time),the mean enhancement time of calf arteries(the average of peak enhancement time of middle anterior tibial artery, middle posterior tibial artery and middle peroneal artery). ES-1000 spectrophotometer was used to detect ABI in 20 patients. Results:1. In 34 patients(67 lower extremities, except one amputation), the bolus arriving time of the popliteal artery is 30.54±6.82s (14.4-47. 1s), the time difference of the bolus arrival in the popliteal artery(33 patients) between the two legs is 2.10±2.43s (0-9.4s), the calf artery transit time is 35.93±17.41s (11.80-78.00s)2. The mean peak enhancement time of calf arteries was much shorter in patients with a ABI less than 0.5 than those with a ABI more than 0.5. However,there was no difference in mean peak enhancement time in bolus arriving time of the popliteal artery and the calf artery transit time. The mean peak enhancement time in calf arteries obtained by TWIST MRA was correlated well with ABI with a Pearson correlation index of 0.589. Conclusion:1. There is marked hemodynamic difference between patients and between bilateral legs of each patient, as a result the use of dynamic TWIST MRA sequence is crucial.2. The mean peak enhancement time in calf arteries can be used as a functional index to reflect clinical ABI index and the degree of lower extremity ischemia. Key words:PAOD, MRA, ABIPart two Comparison of 3.0T TWIST MRA and conventional CE-MRA in the examination of calf artery in PAOD patientsObjective:To evaluate the quality and the diagnostic accuracy of time-resolved imaging with stochastic trajectories Magnetic Resonance Angiography (TWIST MRA) in calf artery in PAOD patients. Materials and Methods:34 patients with confirmed or suspected PAOD received both TWIST MRA and CE-MRA of the lower extremity.3.0T MRI was used. O.1ml/kg Gadolinium contrast agents was used at the TWIST MRA, and then 0.3ml/kg gadolinium was used for CE-MRA at all lower extremity examination. A test bolus of gadolinium(lml) was used to determine the peak enhancement time of aorta (at renal artery level).The calf arteries were divided into 13 segments:the popliteal artery, the tibioperoneal trunk,proximal anterior tibial artery, middle anterior tibial artery, distal anterior tibial artery, proximal posterior tibial artery, middle posterior tibial artery, distal posterior tibial artery, proximal peroneal artery, middle peroneal artery, distal peroneal artery, dorsal arterial arch and plantar arterial arch. Two experienced radiologists evaluated the image quality and the degree of stenosis. The visibility of arterial segments was scored with 0-3 points rating(0=no diagnostic value, and 3 points=good vascular enhancement, strong signal, no artifacts). Venous pollution was scored with 0-3 points rating(0=no venous overlap, and 3 points=venous enhancement, seriously affecting diagnosis, impossible to diagnose).Arterial stenosis were graded with 0-2 point rating (0=normal and mild stenosis (0-49% stenosis); 1 point=significant stenosis (50-99% stenosis); 2 points=occlusion (stenosis 100%).Venous pollution was evaluated per leg. The visibility and degree of stenosis were evaluated per segement of calf artery. Combined TWIST MRA and CE-MRA was used as the diagnostic criteria to evaluate the sensitivity, specificity, positive predictive value and negative predictive value of TWIST MRA and CE-MRA. And DSA was used as the gold standard to evaluate these values of TWIST MRA and CE-MRA in 15 patients who underwent DSA examination.Results:1. The average visibility score of TWIST MRA image was 2.82±0.465, while that of CE-MRA image was 2.77±0.435 with no significant difference between the two. The average visibility score was higher in TWIST MRA than in CE-MRA in the popliteal artery segment.2. Among 67 legs(1 case with one leg amputation), on CE-MRA, there were 35 legs with different degrees of venous enhancement. The mean venous pollution score of TWIST MRA was 0±0 while that score of CE-MRA was 0.67±0.766.3. Using TWIST MRA+CE-MRA as the diagnostic criteria, the sensitivity and specificity of TWIST MRA and CE-MRA in showing normal and mild stenosis were 98.1%,99.7%, and 94.4%,99.2%, in showing significant stenosis 94.6%, 97.3%, and 91.1%,97.1%, in showing occlusion 97.7%,97.9%, and 93.6%, 97.7%. When using DSA as gold standard, both TWIST MRA and CE-MRA also showed very high sensitivity and specificity in evaluating stenosis of all levels.Conclusion:1. There is no difference in visibility of calf artery segments between TWIST MRA and CE-MRA. The visibility of popliteal artery and the tibioperoneal trunk is better in TWIST MRA than in CE-MRA.2. Both TWIST MRA and CE-MRA show very high sensitivity and specificity in evaluating stenosis of different levels at different segements.3. TWIST MRA has no venous pollution in the calf region and has other advantages such as no need of estimating scan delay time,lower dose of contrast and dynamic depiction of calf arteries.4. We can optimize the examination procedure by first examining the calf arteries using TWIST MRA and then examining the abdominal station, pelvic station and thigh station using CE-MRA, so as to eliminating the venous pollution in the calf station.