Robert S. Lees

Imaging human atherosclerosis with 99mTc-labeled low density lipoproteins.

The feasibility of localizing human atherosclerotic plaques by gamma scintillation camera external Imaging with technetlum-99m-labeled low density lipoproteins (Tc-LDL) was tested In 17 patients who had atherosclerosis. Imaging demonstrated focal accumulation of radlolabel consistent with 99mTc-LD L sequestration by plaques In the carotid, lilac, or femoral vessels of four patients 8 to 21 hours after Intravenous Injection of the radlopharmaceutlcal. Focal accumulation of 99mTc-LD L also appeared In the location of coronary lesions In four patients, but this accumulation could not be distinguished with certainty from residual blood pool radioactivity. When carotid endarterectomy specimens from six patients who received 99mTc - LDL 1 day before endarterectomy were examined, the specimens had focal accumulations of radlolabel, with two to four times greater radioactivity In some regions of each specimen than In others; this occurred whether or not the lesions were detected on the gamma camera Images. Lesion composition may have determined whether accumulation was quantitatively sufficient to produce an external Image. Hlstologlcally, the Imaged carotid specimen had abundant foam cells and macrophages and poorly organized Intramural blood consistent with a plaque hemorrhage; in contrast, nonlmaged endarterectomy specimens were mature, fibrocalclfic plaques. We conclude that: 1) 99mTc-LD L did accumulate In human atherosclerotic plaques; 2) In some patients, the accumulation of 99mTc-LD L was sufficient for detection by gamma camera Imaging; 3) the amount of LDL that accumulated appeared to depend on lesion composition; and 4) the design of new radlopharmaceutlcals with reduced residual blood pool activity relative to plaque accumulation should lead to Improved external Imaging of atherosclerosis.

Intraoperative angioscopy: principles of irrigation and description of a new dedicated irrigation pump

The value of intraoperative angioscopy in the detection and immediate correction of technical errors and deficiencies during vascular surgery has been previously documented. The inability to see through blood remains the most significant limitation to the general application of angioscopy. Local irrigation with a balanced salt solution is the most commonly used method to clear the blood from a restricted field in a particular vessel. We have developed a new catheter irrigation pump system (maximum flow rate 340 ml/min) to establish and maintain visibility of the field during intraoperative angioscopy. Furthermore, we have demonstrated the safety of irrigating with high volume flows in the peripheral arteries and defined the basic principles of irrigation for angioscopy. The prototype pump tested in this study provides a wide range of flow rates and permits precise measurements of the fluid delivered. The instruments display and its control with a single foot pedal makes its use relatively simple, obviating the need for additional support personnel while increasing the efficacy and safety of the angioscopic examination and increasing the number of situations where angioscopy may be very useful.

Phonoangiography: qualitative and quantitative

Bruit analysis (phonoangiography) has been performed for many years as a method of characterizing arterial disease. Time displays of arterial bruits, particularly at the carotid bifurcation, have been used in an attempt to quantitate arterial narrowing. Despite the generalization that longer bruits and bruits which look and sound higher in frequency are often associated with severe disease, prospective studies have shown no useful predictive value for qualitative phonoangiography. In marked contrast, spectral bruit analysis or quantitative phonoangiography has been quite accurate in predicting the location and extent of carotid stenosis, and in distinguishing intrinsic from transmitted bruits. With this method, the peak systolic portion of the bruit is subjected to fast Fourier transform analysis. The peak frequency, beyond which amplitude drops as frequency increases further, is directly related to the residual lumen diameter of the stenotic common or internal carotid artery. Several blinded trials of this method have given results accurate to within 1 mm of angiographic values in 83–93% of cases studied. When used in conjunction with duplex doppler ultrasound scanning, 95% accuracy in diagnosis of patients with and without bruits may be achieved. This completely noninvasive method deserves more widespread use and may also be applicable to other cardiovascular sounds.

External Imaging of Active Atherosclerosis with 99mTc-LDL

Atherosclerosis is usually thought of in anatomical or pathological terms. This is understandable since end-organ disease — myocardial infarction, stroke, peripheral vascular disease — is the result of obstructive lesions which impair arterial blood flow. In terms of atherogenesis and detection of early atherosclerosis, however, it may be more useful to think of the disease in metabolic, biochemical, or pathophysiological parameters. The early stages of atherosclerosis are not associated with obstruction to flow, but are rather characterized by biochemical and metabolic changes in the arterial wall.