Interference-free Detection of Lipid-laden Atherosclerotic Plaques by 3D Co-registration of Frequency-Domain Differential Photoacoustic and Ultrasound Radar Imaging.

As lipid composition of atherosclerotic plaques is considered to be one of the primary indicators for plaque vulnerability, a diagnostic modality that can sensitively evaluate their necrotic core is highly desirable in atherosclerosis imaging. In this regard, intravascular photoacoustic (IVPA) imaging is an emerging plaque detection modality that provides lipid-specific chemical information of arterial walls. Within the near-infrared window, a 1210-nm optical source is usually chosen for IVPA applications because lipid exhibits a strong absorption peak at that wavelength. However, other arterial tissues also show some degree of absorption near 1210 nm and generate undesirable interfering PA signals. In this study, a novel wavelength-modulated Intravascular Differential Photoacoustic Radar (IV-DPAR) modality was introduced as an interference-free detection technique for a more accurate and reliable diagnosis of plaque progression. By using two low-power continuous-wave laser diodes in a differential manner, IV-DPAR could efficiently suppress undesirable absorptions and system noise, while dramatically improving system sensitivity and specificity to cholesterol, the primary ingredient of plaque necrotic core. When co-registered with intravascular ultrasound imaging, IV-DPAR could sensitively locate and characterize the lipid contents of plaques in human atherosclerotic arteries, regardless of their size and depth.

Frequency-domain differential photoacoustic radar: theory and validation for ultrasensitive atherosclerotic plaque imaging.

Lipid composition of atherosclerotic plaques is considered to be highly related to plaque vulnerability. Therefore, a specific diagnostic or imaging modality that can sensitively evaluate plaques' necrotic core is desirable in atherosclerosis imaging. In this regard, intravascular photoacoustic (IVPA) imaging is an emerging plaque detection technique that provides lipid-specific chemical information from an arterial wall with great optical contrast and long acoustic penetration depth. While, in the near-infrared window, a 1210-nm optical source is usually chosen for IVPA applications since lipids exhibit a strong absorption peak at that wavelength, the sensitivity problem arises in the conventional single-ended systems as other arterial tissues also show some degree of absorption near that spectral region, thereby generating undesirably interfering photoacoustic (PA) signals. A theory of the high-frequency frequency-domain differential photoacoustic radar (DPAR) modality is introduced as a unique detection technique for accurate and molecularly specific evaluation of vulnerable plaques. By assuming two low-power continuous-wave optical sources at ∼1210 and ∼970 nm in a differential manner, DPAR theory and the corresponding simulation/experiment studies suggest an imaging modality that is only sensitive and specific to the spectroscopically defined imaging target, cholesterol.

Validation of a 40 MHz B-scan ultrasound biomicroscope for the evaluation of osteoarthritis lesions in an animal model.

OBJECTIVE: To evaluate high frequency (40 MHz) B-mode ultrasound for the detection of osteoarthritis (OA) lesions of varying severity in an animal model of OA. DESIGN: Ultrasound biomicroscopy (UBM) was performed on the femoral articular surface of adult rabbits with unilateral transection of the anterior cruciate ligament at 4, 8 and 12 weeks post-surgery and on control rabbits. The articular cartilage was examined and graded macroscopically and histologically for OA lesions. Histological examination was used as a reference to determine sensitivity and specificity of ultrasonographic and macroscopic examination regarding fibrillation and ulceration of articular cartilage. RESULTS: Identification of slight surface irregularities was made possible with UBM. The sensitivity and specificity of UBM were 92.3% and 96.4%, respectively, to detect histological fibrillation and 90.9% and 97.6%, respectively, to identify histological ulceration. Macroscopic examination using India Ink had a sensitivity and specificity of 80% and 96.4%, respectively, for fibrillation and 90.9% and 90.5%, respectively, for ulceration when compared to histology. A high correlation (rsp=0.90) was found between ultrasonographic and histological scores. CONCLUSIONS: UBM of articular cartilage reflects histological structure and can accurately detect early changes such as fibrillation. UBM has the potential to be a valuable tool for the in vivo identification of early lesions of OA and for monitoring the disease or efficacy of novel therapy if it can be packaged in a minimally invasive format suitable for intra-articular imaging.