Background: In peripheral artery disease, two different types of calcifications are frequently observed, i.e., medial and intimal calcification.
Aims: The aim of this study is to determine the ability of intra-vessel ultrasound imaging (IVUS) and optical frequency domain imaging (OFDI) to detect medial and intimal calcification in human peripheral arteries.
Methods: We performed ex vivo intravascular imaging of cadaveric human peripheral arteries with calcifications. IVUS and OFDI images were co-registered with histology. A total 12 legs from 9 patients were examined, and 438 cross-sectional images were co-registered with histology. Results: OFDI could detected 183 of 231 intimal calcification by histology, whereas IVUS could detect 194 [OFDI; sensitivity, 79%, specificity, 86%, area under the curve (AUC), 0.83; IVUS; sensitivity, 84%, specificity, 85%, AUC, 0.85]. Of 245 medial calcifications by histology, 160 and 164 were detected by OFDI and IVUS, respectively (OFDI; sensitivity, 65%, specificity, 85%, AUC, 0.75; IVUS; sensitivity, 67%, specificity, 80%, AUC, 0.74). Medial calcification with overlying intimal calcification (overlapped calcification) and unclear border between intima and media were the main reasons for misdiagnosis. Without those 89 overlapped calcifications, sensitivity in both OFDI and IVUS was improved (OFDI; sensitivity, 81%, specificity, 85%, AUC, 0.83; IVUS; sensitivity, 88%, specificity, 80%, AUC, 0.84).
Conclusions: There are limitation in detecting medial calcification in overlapped intimal calcification and with unclear border between intima and media by both IVUS and OFDI. It is important to distinguish medial calcification from intimal calcification before proceeding with endovascular therapy since different approaches should be required.