X-ray imaging technique for in vitro tissue composition measurements using saline/iodine displacement: technique optimization

In vitro investigation of calcium distribution and tissue thickness in the human thoracic aorta

Atherosclerosis represents a significant cause of morbidity and mortality in the western world. Manifestations of atherosclerotic disease among the elderly include the development of raised lesions that often include calcified regions with material properties similar to bone. There is little information available about the amount and distribution of these calcified plaques within the human aorta, partly due to the difficulty in obtaining this information during in vivo studies. We report the results of a cadaveric investigation of thoracic aortic wall thickness, diameter and calcium content. A non-destructive x-ray imaging technique was used to obtain two-dimensional maps of total thickness and mineral content in excised thoracic aortic specimens. In a study of 39 individuals (23 male and 16 female, aged 20-92 years) we report a significant non-linear correlation between calcium burden and age, with calcium deposition most commonly occurring proximal to the ostia of major branching vessels. We also found a significant linear correlation between age and both total aortic wall thickness and aortic diameter. An improved understanding of the pathological changes in the ageing thoracic aorta may be useful in the development of strategies to reduce the undesirable vessel calcification associated with atherosclerosis.

X-ray imaging technique for in vitro tissue composition measurements using saline/iodine displacement: experimental verification

A novel in vitro radiographic technique using saline/iodine displacement, which can be used to study the bone-equivalent and soft-tissue-equivalent thicknesses within vessel walls, was applied to imaging of arterial specimens. Results concerning the accuracy and precision of the bone-equivalent and soft-tissue-equivalent thickness measurements obtained with this technique are reported and discussed. Planar radiographs of a phantom were obtained under two different conditions: (1) when it is immersed in an isotonic saline solution using a 45-kVp spectrum with no added filtration, and (2) when it is immersed in a concentrated iodine solution using a 100-kVp spectrum with 12.5-mm aluminum-added filtration. Calibration step wedges made out of bone-mimicking and soft-tissue-mimicking materials are imaged simultaneously to generate calibration curves that are used to convert the radiographs into bone-equivalent and total-thickness images. A soft-tissue-thickness image is obtained from the subtraction of the bone-equivalent image from the total-thickness image. Thickness measurements obtained from these images yielded average accuracies of +/- 110 microns for both the bone-equivalent and the soft-tissue-equivalent images. The precision (one standard deviation) of the thickness measurements was +/- 60 and +/- 90 microns for the bone-equivalent and the soft-tissue-equivalent images, respectively. In conclusion, since calcified plaque can become as thick as 3-4 mm, the saline/iodine displacement technique has the potential to be a very useful technique for ex vivo studies of the progression of atherosclerosis because of its high accuracy and precision.