In Vivo Vibroacoustography of Large Peripheral Arteries

Abstract

Objective-Vibroacoustography allows imaging of objects on the basis of their acoustic signal emitted during low-frequency (kHz) vibrations produced by 2 intersecting ultrasound beams at slightly different frequencies. This study tested the feasibility of using vibroacoustography to distinguish between normal and calcified femoral arteries in a pig model. Materials and Methods-Thirteen normal porcine femoral arteries, 7 with experimentally induced arterial calcifications, and 1 control artery injected with saline only were scanned in vivo. Images were obtained at 45 kHz using a 3 MHz confocal transducer. The acoustic emission signal was detected with a hydrophone placed on the animal's limb. Images were reconstructed on the basis of the amplitude of the acoustic emission signal. Vessel patency, vessel dimensions, and the extent of calcified plaques were confirmed in vivo by angiography and conventional ultrasound. Excised arteries were reexamined with vibroacoustography, X-ray radiography, and histology.Results-In vivo, vibroacoustography produced high-resolution, speckle-free images with a high level of anatomic detail. Measurements of femoral artery diameter were similar by vibroacoustography and conventional ultrasound (mean difference ± SD, 0.1 ± 0.4 mm). Calcified plaque area measured by different methods was comparable (vibroacoustography, in vivo: 1.0 ± 0.9 cm 2 ; vibroacoustography in vitro: 1.1 ± 0.6 cm 2 ; X-ray radiography: 0.9 ± 0.6 cm 2 ). The reproducibility of measurements was high. Sensitivity and specificity for detecting calcifications were 100% and 86%, respectively, and positive and negative predictive values were 77% and 100%, respectively. Computed tomography (CT) is currently the most widely used noninvasive imaging modality for the quantitative assessment of total calcium burden on the cardiovascular system. However, there are concerns regarding the reproducibility of CT 11 and the X-ray exposure of sequential scanning, for example, to follow the effects of therapeutic interventions. 12-15 Conclusions-VibroacoustographyVibroacoustography is a new ultrasound-based method to detect vascular calcifications. 16-18 This technique uses acoustic radiation pressure produced by 2 intersecting ultrasound beams at slightly different frequencies to induce a vibration (kHz range) of the object from a distance. The image of the object is obtained on the basis of the vibration-induced acoustic emission signal. This signal depends on the stiffness as well as the acoustic properties of the object. 17, 19Vibroacoustography can easily detect calcified deposits in excised tissue specimens scanned in a water bath. The resulting images faithfully resemble X-ray images of specimens. 16-22 However, in vivo, numerous factors could distort the ultrasound and acoustic emission signals.To our knowledge, this is the first in vivo study to test the ability of vibroacoustography to image normal femoral arteries and to detect calcified plaques in femoral arteries of anesthetized swine, an animal model that allows...

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