Computed tomography angiography (CTA) has become in large part for imaging the peripheral artery system in clinical practice¹. However, the presence of vascular wall calcification limits the evaluation of arterial patency in CTA, then the evaluation with curved MPR or thin slice axial images are required, but these processes are time-consuming and cumbersome. Recently, an automatic calcification removable tool has been developed, which can remove arterial wall calcification by post-processing in short time².

Fresh blood imaging (FBI) is a non-contrast enhanced 3D MR angiography technique, which using a physiological signal change of an artery during a cardiac cycle³. FBI was reported to offer an excellent diagnostic capability comparable to CTA⁴.

The purpose of this study is to compare the diagnostic ability of FBI with that of CTA using a calcification removal tool in the evaluation of the lower-extremity arteries with wall calcifications.

This study was approved by the institutional review board, and informed consent was obtained. Twenty consecutive patients (10 men and 10 women [mean age, 72.6 y.o.]) underwent both FBI and CTA examinations. The arterial vascular system was divided into 19 anatomic segments, from which a total of 131 arterial segments with wall calcification was included in this study.

All MR examinations were performed on a 1.5-T clinical imager (EXCELART Vantage powered by Atlas, Toshiba Medical Systems Corp., Japan) using a combination of an Atlas SPEEDER body and an Atlas SPEEDER spine coil. After acquiring diastolic and systolic ECG-triggered 3D data, the system automatically performed the systolic-diastolic subtraction, and then a maximum intensity projection (MIP) processing. All CTA studies were examined on a 64-detector row CT scanner and 320-detector row CT scanner (Aquilion 64 and Aquilion One; Toshiba Medical Systems Corp., Japan) with 1 mm slice thickness. Maximum intensity projection images (CTA-MIP) and calcification removed MIP images (CTA-MIP w/o Ca) were created on a clinical image workstation (Synapse Vincent, Fuji medical systems, Tokyo).

The degree of arterial wall calcification was divided into three categories; “severe” is 50% or more luminal narrowing due to wall calcification, “moderate” is from 10 to 50%, “mild” is less than 10%. Each segment was graded for degree of stenosis using a five-point grading system (grade 1, <10% of stenosis; grade 2, 10%-49%; grade 3, 50%-99%; grade 4, occlusion; and grade 5, nondiagnostic) by three observers with consensus. Sensitivity, specificity, and accuracy for detection of 50% or greater stenotic lesions using FBI, CTA-MIP, and CTA-MIP w/o Ca were calculated. “Truth” of the stenosis was determined by the clinical information, thin slice axial CT images, curved MPR, and source images of FBI.

In all segments, FBI provided diagnostic images regardless of the degree of wall calcification. On the contrary, CTA-MIP and CTA-MIP w/o Ca were strongly affected by calcification, and the segments which could be evaluated were15.2% in CTA-MIP, 28.3% in CTA-MIP w/o Ca in severe wall calcification; 54.2% in CTA-MIP, 67.9% in CTA-MIP w/o Ca in moderate wall calcification. Mild calcification had little effect to luminal evaluation. (Fig. 1)

The overall sensitivity, specificity, and accuracy of FBI were 0.80%, 0.98%, and 0.92%, respectively. The diagnostic ability of FBI showed no significant difference between the calcification grades. (Fig. 2). CTA-MIP showed good diagnostic performance in the segment with mild wall calcification with using multi-directional observation (accuracy 0.94%). However it was difficult to evaluate the luminal changes in most of the moderate and all of the severe calcification cases.

In some cases with mild calcification or localized moderate calcification, the calcification was sufficiently removed then it became easier to evaluate luminal narrowing than those before calcification removal (Figure 3). However, the calcium removal was not useful in the cases with moderate and severe wall calcification (Figure 4). In the calf region, the effects of calcification removal were hardly observed.

FBI provided good quality arterial images even in the case with severe wall calcification. The diagnostic ability of FBI was significantly superior to that of CTA-MIP and CTA-MIP w/o Ca in the moderate to severe calcified arterial segments.

In conclusion, FBI is an accurate and noninvasive alternative to CTA for the assessment of aortoiliac and lower extremity arteries in patients with PAD.