Requirements for the detection of atherosclerosis lesions in carotid arteries with Single Photon Emission Computed Tomography

Abstract

Thesis (Ph.D.)--Harvard--Massachusetts Institute of Technology Division of Health Sciences and Technology, 2000.Includes bibliographical references (leaves 135-139).Detecting the metabolic state of atherosclerotic lesions is a promise of nuclear medicine imaging. Several researchers are developing radiopharmaceuticals for atherosclerosis imaging. In this thesis, we provided procedural guidelines to detect carotid lesions with single photon ,Emission Computed Tomography (SPECT). We first established a method to assess the requirements for "successful" lesion detection. Although this method was used to detect focal carotid lesions, it is also applicable to the detection of focal lesions in other arteries or veins. We measured lesion detectability using the output values of a 3D moving Non Pre-Whitening Matched Filter (30 mNPWMF) with the .Localization Receiver Operating Characteristics (LROC) paradigm. We simulated SPECT images of the neck using SimSPECT, our in-house analog Monte Carlo radiation transport code. We used 400 64x64 reconstructed images formed by 99mTc photons of a focal lesion in a carotid artery next to a jugular vein, both in a cylindrical water neck. We then applied the 3D \ mNPWMF along the large neck vessels. The NPWMF has been found to correlate well with human observers in simple ROC studies. We expect the mNPWMF operation to mimic a radiologist who already has a blood pool image which identifies the location of the large neck vessels. Using this detection method, we calculated that 1 to 6 kBq/cm were needed in the lesion. At large blood activity (4.6 times the surrounding tissue activity), the minimum radiopharmaceutical uptake increased by 1.6-2.9 times when the patient was lying down as opposed to sitting up. At this blood activity, a carotid dilation of 1 cm radius distracted the moving Matched Filter from lesion detection. We recommend that the blood activity be as low as possible to avoid any focal dilation from distracting our detector. We recommend that, at high blood activity, the patient be imaged in an upright position in which the jugular veins are collapsed, preventing their blood pool activity from obscuring the carotid arteries. Finally, we showed that a lesion needed 140% of the radiopharmaceutical when acquired with a radius of rotation (ROR) of25 cm instead of 15 cm. In conclusion, we assessed successfully the effect of the jugular veins and carotid dilation on detection of carotid lesions in SPECT images of the neck using the LROC detection paradigm.by Marie-José Bélanger.Ph.D