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Imaging Human Atherosclerosis with ""To-labeled Low Density Lipoproteins Ann M. Lees, Robert S. Lees, Frederick J. Schoen, Jonathan L. Isaacsohn, Alan J. Fischman, Kenneth A. McKusick, and H. William Strauss Downloaded from http://atvb.ahajournals.org/ by guest on May 14, 2017 The feasibility of localizing human atherosclerotic plaques by gamma scintillation camera external Imaging with technetlum-99m-labeled low density lipoproteins ( T c - L D L ) was tested In 17 patients who had atherosclerosis. Imaging demonstrated focal accumulation of radlolabel consistent with T c - L D 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 T c - L D 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 T c 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) T c - L D L did accumulate In human atherosclerotic plaques; 2) In some patients, the accumulation of T c - L D 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. (Arteriosclerosis 8:461-470, September/October 1988) D Dilation camera has been investigated, with the hope that it will be useful for localizing lesions, including those likely to lead to clinical complications as a result of acute plaque changes,7 and for evaluating the efficacy of medical treatment of hypertipidemia and hypertension at periodic intervals. In contrast to current methods, the new technique depends on locating atherosclerotic plaques by their intramural accumulation of radiolabel after injection of a suitable radiopharmaceutical. etection of atherosclerotic plaques by means other than their space-occupying characteristics might permit localization of lesions at an earlier stage than is now possible. Although vascular surgery,1-2 and, more recently, balloon angioplasty and thrombolytic therapy 34 have allowed tissue salvage in many patients with advanced atherosclerosis, prevention or arrest of the disease before critical stenosis develops would be preferable.58 Furthermore, identification of patients at high risk for acute complications from asymptomatic plaques might permit beneficial changes in patient management. As an approach to these goals, a new noninvasive method to detect and characterize atherosclerotic plaques with the gamma scin- Since low density lipoproteins (LDL) had previously been shown to be present in atheromata,8-11 we used radiolabeled LDL as a probe for arterial lesions. Noninvasive external imaging of atherosclerosis appeared feasible when it was found that 12sl-labeled-LDL accumulated focally in experimental arterial lesions In normocholesterolemic rabbits.12 In a subsequent pilot study with human subjects, we showed that carotid atherosclerosis could be imaged with 12S l-labeled LDL.13 Since this isotope is not optimal for external imaging with the gamma camera, a method was developed14 for labeling LDL with T c ( T c - L D L ) . The new radiopharmaceutical not only provided clear external images of experimental arterial lesions in animals, but also, based on urinary excretion, appeared to be partially trapped in tissues.14 In the present study, T c - L D L was administered to 17 human subjects to evaluate the possibility that human atherosclerotic lesions could accumulate enough From the Arteriosclerosis Center, Department cf Medicine, New England Deaconess Hospital, Department of Applied Biological Sciences, Massachusetts Institute of Technology, Departments of Medicine and Radiology, Massachusetts General Hospital, and Department of Pathology, Brigham and Women's Hospital, Boston, Massachusetts. This research was supported in part by Grants HL32975 and HL07416 from the National Heart, Lung, and Blood Institute, National Institutes of Health. This work was presented in part at the 58th Scientific Sessions of the American Heart Association, Washington, DC, November 1985, and has previously appeared in abstract form (Circulation 1985 72; part 11:111-198). Address for correspondence: Dr. Robert S. Lees, 110 Francis Street, Suite 7F, Boston, MA 02215. Received December 29,1987; revision accepted April 5,1988. 461 462 ARTERIOSCLEROSIS VOL 8, No 5, SEPTEMBER/OCTOBER 1988 radiolabel to permit external imaging with the gamma camera, and in carotid endarterectomy specimens from six of the subjects, to determine the distribution of radiolabel within atherosclerotic lesions and correlate tissue composition with the ability to obtain an external image. Methods Patients Downloaded from http://atvb.ahajournals.org/ by guest on May 14, 2017 Seventeen patients were recruited from the Arteriosclerosis Center's outpatient clinic and from among the patients of physicians at the Massachusetts General and New England Deaconess Hospitals. Signed statements of consent were obtained from each patient after the nature of the study had been fully explained. Pertinent data for each patient are outlined in Table 1. Six patients (Nos. 3,4,7,8, 10, and 14) underwent carotid endarterectomy after imaging, and their surgical specimens were available for measurement of radioactivity and histologic study. Seven patients (Nos. 1, 2, 3, 7, 10, 11, and 12) were on lipidlowering medications, with varying degrees of success. Preparation of Radlolabeled Low Density Llpoproteln On Day 1, 100 ml of blood was drawn from an antecubital vein under sterile precautions and the patient's LDL was isolated on Day 1 and Day 2 by sequential ultracentrifugation as described previously.1315 On Day 3, the LDL was radiolabeled with " T c under sterile conditions, as follows. Two to 6 mg of LDL (at a density of 1.050 g/ml) were placed in an empty sterile vial. To the vial was added 70 to 100 mCi of sodium ""pertechnetate (E.I. du Pont de Nemours & Company, North Billerica, MA). The reactants were mixed, and to them was added 10 mg of sodium dithionite dissolved immediately before use in 0.1 ml of 0.5 M glycine buffer (pH 9.8). The total volume of the reaction mixture was about 1.1 ml. This mixture was allowed to stand at room temperature for 30 minutes (20 minutes for Patients 1 and 7); then it was chromatcgraphed on a sterile 2.5 x 10 cm disposable Sephadex G-50 column (Pharmacia Incorporated, Piscataway, NJ) which was pre-equilibrated with sterile 0.15 M sodium chloride brought to pH 8 with sterile sodium bicarbonate buffer. After a volume equal to that of the reaction mixture was allowed to flow through the column, 7.5 ml of the saline/bicarbonate buffer was used to elirte the column. The first 4 ml of eluate was discarded. The next 3.5 ml, which contained the " T c - L D L , was collected in a sterile 30 ml technetium elution vial (E.I. du Pont de Nemours & Company). The term """Tc-LDL", as used throughout this report, refers to the 3.5 ml of eluate obtained from the Sephadex G-50 column. It had been previously shown by ultracentrifugation and paper electrophoresis that this preparation consisted predominantly of 96nTc tightly bound to LDL along with a much smaller, variable amount of macromolecular inorganic technetium species.14 In the present study, each preparation was filtered through a 0.22/tm filter just before use, and a small aliquot was analyzed by paper electrophoresis as described previously.14 In each case, the major peak was that of " T c - L D L , similar to the published example, with a vari- able amount of radioactivity which, as reported previously, did not stain with oil red O after paper electrophoresis. Imaging The patients were immediately imaged with either a standard or a large field-of-view gamma camera equipped with an all-purpose parallel-hole collimator, and then imaged again one to three times up to 25 hours after injection of 10 to 20 mCi of T c - L D L . Anterior cervical and thoracic views, anterior and posterior abdominal views, and anterior views of the pelvis and lower extremities were recorded in all patients; additional views were recorded when appropriate. Images were obtained for up to 10B counts for each view, or up to 15 minutes at the later imaging times. All images were reviewed by three nuclear medicine physicians. Only regions of arterial accumulation identified as positive by all three reviewers were called positive. Specimen Analysis Six carotid endarterectomy specimens were available for direct examination; specimens of other arteries were not available for analysis. After gross photography, the carotid endarterectomy specimens were rinsed in normal saline until the rinses were free of blood, and then divided into three to four sections of differing atherosclerotic involvement based on the degree of mural thickening and stenosis. The tissues were blotted lightly before being weighed and were then counted in a gamma counter (Packard 5630, Packard Instrument Corporation, Des Plaines, IL). After measurement of radioactivity, the sections of each carotid endarterectomy specimen were fixed in 10% formalin, embedded in paraffin, cut in cross-section for light microscopy, and stained with hematoxylin and eosin. A maximum of 2 hours elapsed between the time carotid specimens were removed surgically and the time they were placed in fixative. To determine the percent of injected T c that was excreted in urine, 24-hour urine collections were obtained, measured, and counted in three patients. Definitions A positive gamma scintillation camera image was defined as the appearance of focal radiolabel accumulation in the region of a vessel visible above the blood pool that increased in intensity over time relative to blood pool radioactivity and was asymmetric relative to the contralateral vessel. In carotid endarterectomy specimens, focal accumulation was defined as higher levels of radioactivity in some regions of the specimen and lower levels elsewhere. The histologic sections of carotid specimens were classified by a semiquantitative assessment of the fraction of each section that had abundant macrophages and foam cells, and/or hematoma or necrosis (Category A) relative to the fraction of the section that was mature fibrous connective tissue, with or without areas of calcification (Category B). The primary distinction was between tissue in which the functional metabolic status and/or the structural organization appeared to be evolving IMAGING HUMAN ATHEROSCLEROSIS 463 Lees et al. .r'-\ ju^lungs /'" •;i.h e a r t £ U ^ = ••:••• P .I $: . Downloaded from http://atvb.ahajournals.org/ by guest on May 14, 2017 &-/C small bowel large-^ bowel ; cecum Figure 1. Anterior sdntigram of Patient 13 at: A. 10 minutes, B. 1 hour, C. 4 hours, and D. 15 hours after Intravenous Injection of 20.4 mCi of T c - L D L . In A and B, organs with a large blood pool (including the heart, liver, and lungs) were prominent. With increasing time after injection, the cardiac radioactivity (a blood pool marker) decreased, while radioactivity In the other organs (liver, intestine, and kidneys) increased relative to the heart, suggesting a shift of radiolabel from blood into tissue. This patient had no focal vascular accumulation of radiolabel. and tissue which appeared to be quiescent. Since the regions within the plaques were not sharply delineated, exact morphometric measurements of the specimens could not be made. Tissue in Category A had more than 50% dense inflammatory infiltrate with or without abundant macrophages and foam cells, and/or unorganized or incompletely organized intramural blood or focal necrotic debris. Tissue in Category B was mature fibrous connective tissue, which contained smooth muscle cells and/or fibroblasts, with or without dystrophic calcification. "Intermediate tissue" was sparseiy cellular and densely fibrocalcific, with only small regions of macrophages, foam cells, hemorrhage, or necrosis. Results Sclntlgraphy The typical appearance of sequential gamma camera images of a patient given ""Tc-LDL is illustrated in Figure 1. Immediately after injection of the radiolabel, blood pool radioactivity was evident in several organs. Over a 15hour period, the cardiac radioactivity decreased, while radioactivity in the liver, intestine, and kidney increased relative to the heart. The shift in relative radioactivity from the heart, which is a blood pool marker, to organs known to metabolize LDL 1617 was consistent with the transfer of radioactivity from blood to tissue and indicated that the radiopharmaceutical had the biological characteristics of native LDL 1 8 1 7 Four patients (Table 1, Nos. 1 to 4) accumulated sufficient ""Tc-LDL to produce images with the gamma camera in locations where atherosclerotic arterial lesions were known or likely to be present; four patients (Nos. 2, 5, 6, and 9) accumulated radloiabel in areas of the heart anatomically consistent with the location of coronary arteries known or likely to be atherosclerotic, but these areas could not be distinguished with certainty from blood pool radioactivity; ten patients (Nos. 7, 8, and 10 to 17) had no focal arterial accumulation of radiolabel. The doses of T c - L D L for each patient and the time parameters of imaging are listed in Table 2. Arteries with focal accumulation of radiolabel that was consistent with a positive image included the iliac, femoral, and carotid vessels. Patients 1, 2, and 4 had images of the iliac and/or femoral arteries. Patient 1, who had a 464 ARTERIOSCLEROSIS VOL 8, No 5, SEPTEMBER/OCTOBER 1988 Table 1. Patients Studied: Clinical Data and Results Patient no. 1 Age (yrs) Sex TC* TGt 44 M 224 66 Vascular events or symptoms^ TIA 5 yre R carotid endarterectomy None 5 yre Angina Ml Ml M 199 248 Claudication Angina 4 72 M 201 95 Carotid bruit Ml Downloaded from http://atvb.ahajournals.org/ by guest on May 14, 2017 M 132 60 7 8 55 56 F M 533 174 172 91 9 58 M 296 132 10 59 M 176 84 11 12 13 14 15 16 60 60 62 65 65 66 M M M F M F 145 306 218 224 223 294 125 105 84 125 190 503 Iliofemoral 6 yrs 49 48 + L carotid endarterectomy 3 6 4.5 yre 6 yre 105 149 Region with positive image TIA 209 146 Current symptoms R femoral embolectomy M M Time before Imaging 10 yre 48 42 Related vascular procedure^ Claudication 2 5 Time before imaging Femoral bruits TIA Ml Ml Angina 3 yre 10.5 yre 7 yre 10 yre None None None 10 yre 1 wk Coronary bypass Carotid angiogram None 17 yre 11 yre 4 wks 2 yre 1 wk 4.3 yre Ml 1 mo Angina L carotid bruit 6 yre 6 yre R carotid bruit TIA TIA 8 mos 1 wk 13 mos TIA None Carotid angiogram Coronary angiogram Coronary t-PA Coronary angioplasty Coronary angioplasty None L carotid endarterectomy None Carotid angiogram — + — — — + Femoral 2.5 yre 5 days — — - Carotid - Femoral 5 days + 2 yre 1 wk + 4.5 yre - 1 mo + + 8 mos L carotid endarterectomy Carotid artertogram 13 days + 15 days + Angina 6 mos 6 wks + TIA Ml TIA 9 yre 6 yre 3 wks Coronary angioplasty None Coronary bypass Carotid angiogram Claudication Claudication 19 yre 20 yre 6 yre 5 days 19 yre 20 yre TIA 9 yre 5 mos Positive exercise test Ml 3.5 wks Angina L carotid bruit 7 yre 7 yre R carotid bruit Angina Ml Ml Angina Ml Stroke Claudication 7 yre 15 yre 5 yre 2 wks 16 yre 12 yre 4 yre 2 yre Coronary angiogram None Carotid angiogram L carotid endarterectomy Carotid angiogram None Coronary angiogram Coronary angiogram None None None Aortoiliac graft + — 5 days 13 mos Aortoiliac endarterectomies None Coronary angiogram + — 20 mos L carotid endarterectomy Femoral grafts Carotid spectmen§ + + — + + + — 5 mos 1 day + — + 12 days 7 days + 12 days — 5 days 4 days + — — — 6 mos - IMAGING HUMAN ATHEROSCLEROSIS Table 1. Patient Lees et al. 465 (Continued) no. Age (yrs) Sex TC* TGf 17 75 M 379 196 Vascular events or symptoms* Stroke L carotid stenosis R carotid stenosis Coronary insufficiency Coronary insufficiency Time before Imaging Related vascular procedure* Time before imaging Current symptoms — 7yrs — 5yrs — 16 yrs 7 yrs None L carotid endarterectomy 5 yrs R. Carotid endarterectomy 9 yrs None — - 5 yrs None — — Region with positive image Carotid specimen§ *TC = total plasma cholesterol (mg/dl); fTC = plasma triglycerides (mg/dl); $L = left, R = right, Ml = myocardial infarction, TIA = transient ischemic attack, t-PA = tissue plasminogen activator; §Carotid specimen = carotid endarterectomy specimen obtained for counting of radioactivity and histological examination. Downloaded from http://atvb.ahajournals.org/ by guest on May 14, 2017 10-year history of bilateral claudication, had asymmetrical accumulation of radiolabel at several points in the iliofemoral system on the 21-hour images (Figure 2). Patient 2 had a 10-year history of left calf claudication and had left calf claudication at the time of imaging; his 8-hour and 21-hour images showed focal, asymmetric, accumulation of radiolabel in the region of the left femoral artery. Patient 4 had a history of generalized atherosclerosis including recent carotid artery symptoms; although his carotid circulation did not image, his right femoral artery showed focal accumulation of radiolabel at 16 hours. In addition to the femoral disease described above, Patient 2 also had had a myocardial infarction 10 years before his imaging study. At the time of imaging, he denied cardiac symptoms, but his physical examination and electrocardiogram were consistent with severe coronary artery disease. The 8-hour image showed focal, linear accumulation of radiolabel in an area of the heart that was anatomically consistent with the left anterior descending (LAD) coronary artery; however, the accumulation could not be unequivocally distinguished from blood pool radioactivity. The same problem of interpretation occurred in patients 6 and 9. In Patient 6, focal accumulation in the area of the LAD was evident in the 14-hour and the 22-hour images; angioplasty of the patients LAD artery had been performed 4.5 years before the imaging study. One month before the study, an angiogram showed diffuse atherosclerosis of the LAD coronary artery and tight stenosis of the circumflex artery on which angioplasty was performed; no focal accumulation of radiolabel was evident in the area of the circumflex artery in the imaging study. Patient 9 developed exerrjonal chest pain 6 months before his imaging study and underwent coronary angioplasty of the LAD artery 6 weeks before imaging. In the 2-hour and 16-hour images, there was focal accumulation of radiolabel in the area of the LAD artery, which intensified over time, but could not clearly be distinguished from blood pool radioactivity. Uncertainty about a coronary image also occurred with Patient 5, who had an occluded right coronary artery recanalized by intracoronary injection of tissue plasminogen activator 1 week before imaging. Focal accumulation of radiolabel anatomically consistent with the location of the proximal right coronary artery was visible on the 16-hour image but could not be distinguished with certainty from blood pool radioactivity. Patient 3 had a 9-hour image (Figures 3A and 3B) which showed asymmetrical focal accumulation of radiolabel in the right internal carotid artery. An angiogram performed before right carotid endarterectomy (Figure 3C) showed tight stenosis of the right internal, and moderate stenosis of the left internal, carotid arteries. These lesions were associated with the recent onset of a prominent high-pitched right carotid bruit and no bruit on the left. At surgery, a brown-stained tightly stenotic right carotid lesion was removed, which appeared on gross examination to have an organized, relatively recent intramural hemorrhage (Figure 3D). Histology Histologic examination of arterial specimens from the six carotid endarterectomy patients made possible a Table 2. Patient no. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 Dose and Time Parameters of Imaging Tc-LDL injected (mCl) Time of positive images (hrs) Duration of imaging study (hrs) 18.6 21 21 21.0 13.3 16.4 8,21 21 21.3 13.0 18.9 21.6 14.7 9 9 16 — — — — — 16 16 22 20 9 16 14 — — — 21 21 12.1 20.5 18.2 — — — — 25 5* 16 20 10.0 — 23 19.8 19.5 19.3 20.4 'Later images could not be obtained because of surgical scheduling. 466 ARTERIOSCLEROSIS VOL 8, No 5, SEPTEMBER/OCTOBER 1988 I transverse colon : • % . ' ' % ' - . - • - - ' .iliac:^ vv.V:^^-:| Downloaded from http://atvb.ahajournals.org/ by guest on May 14, 2017 : bladder/ VT # *•;•' • •vt •S external %^ Iliac ' . \ ' - - • - • • ' . . :•'. - j.Xfemoral '•;. •/ 7 / artery f geiiitalia Figure 2. Anterior sdntJgram of Patient 1 at 21 hours after Intravenous Injection of 18.6 mCi of T c - L D L . The field of view Included the area between the umbilicus and mid-thigh. In addition to accumulation in bowel and genitalia, the distribution of radiolabel in the iliac and femoral vessels was asymmetrically Irregular (arrows). correlation between lesion composition as assessed by the light microscopic appearance and the ability to image. The area of tight stenosis in the imageable lesion of Patient 3 was largely composed of poorly organized intramural hematoma with abundant foam cells and macrophages (Figure. 3E). In contrast, the other five carotid specimens, which did not image, were more fibrocalcific than cellular, hemorrhagic, or necrotjc. For example, the right carotid artery of Patient 7, which did not image, appeared tightly stenosed on angkxjram (Figure 4A). At surgery, a small, stenotic lesion was removed (Figure 4B) which was too small and hard to be cut into sections. The specimen was almost entirely fibrous tissue, with focal calcification and little cellularity (Figure 4C). The lesions in Patients 4, 8, and 14 were also predominantly fibrous, while the lesion in Patient 10 was intermediate with some cellular-hemorrhagic areas and other areas which were fibrotjc. Focal Radioactivity of Carotid Specimens Although the carotid lesions of five carotid endarterectomy patients (Nos. 4,7, 8,10, and 14) did not accumulate enough radiolabel to be visible above the blood pool on external imaging, the five carotid specimens that could be sectioned (including that of Patient 3, which did image) showed focal accumulation of radioactivity, with up to two to four times more radioactivity in the centers of plaques than elsewhere in the specimens (Table 3). Because of the complexity of the studies, it was not feasible to obtain serial blood samples to measure the average plasma radioactivity, which is necessary to make quantitative comparisons of LDL accumulation among the specimens. In addition, surgical scheduling precluded the possibility of obtaining all the carotid specimens at the same time after injection of ""Tc-LDL. However, even with these limitations in mind, it was clear that the difference in radiolabel accumulation by Patient 3's specimen, which imaged, and the other carotid specimens was marked. The anterior and posterior portions from the center of Patient 3's plaque accumulated 20 x i O " ^ and 18x10"*%, respectively, of the injected dose per gram. In contrast, the two center portions of the fibrotic lesion of Patient 4 accumulated less than 1 x 10"*% of the injected dose per gram. Radiolabel accumulation by other fibrotic lesions was similar. The historically intermediate lesion of Patient 10 accumulated no more than 2 x 10~*% of the injected dose per gram in any portion of the specimen. Urine Radioactivity Cumulative urinary excretion of T c - L D L was measured in three patients. Over a 24-hour period from the IMAGING HUMAN ATHEROSCLEROSIS Lees et al. internal .carotid external jugulars Downloaded from http://atvb.ahajournals.org/ by guest on May 14, 2017 B Figure 3. Imaging studies and pathology of carotid stenosis in Patient 3. A. External image 9 hours after injection of 13.1 mCi of T c - L D L showing focal, asymmetrical accumulation of radiolabel in the right distal common carotid artery at the carotid bifurcation and the proximal internal carotid artery (arrows). B. Sketch of A. C. Right carotid angiogram showing extensive stenosis (large arrow) and mural irregularities (small arrows) involving the distal common and proximal internal carotid arteries. This corresponded to the region of accumulation of T c - L D L in the gamma camera image. The left carotid angiogram showed only a minor degree of internal carotid stenosis. D. Photograph of bisected right carotid endarterectomy specimen showing the tight stenosis (arrow) and the long underlying, poorly organized deep hematoma covered by a fibrous cap. E. Photomicrograph of lesion showing numerous foam cells and macrophage giant cells adjacent to a poorly organized intramural hematoma. Hematoxylin and eosin stain, x 200 467 468 ARTERIOSCLEROSIS V O L 8, No 5, SEPTEMBER/OCTOBER 1988 Downloaded from http://atvb.ahajournals.org/ by guest on May 14, 2017 B Figure 4. Angiogram and pathology of carotid stenosis In Patient 7. This patient had no focal vascular accumulation of radblabel. A. Right carotid angiogram showing a tight stenosis at the origin of the Internal carotid artery (arrow). B. Photograph of bisected right carotid endarterectomy specimen. The stenosis (arrow) was apparent, although the calcific composition of the lesion was not visible in the photograph. C. Photomicrograph of lesion. There is a mature, fibrous plaque, with rare macrophages and foam cells. Hematoxyiln and eosln stain. x200 time of injection, the results, expressed as the percent of injected dose excreted, were 4%, 11%, and 12% for Patients 4, 5, and 8, respectively. Discussion The goal of this study was to demonstrate the feasibility of detecting atherosclerotic plaques by their intramural accumulation of a radiopharmaceutical, rather than by their space-occupying characteristics, as is current practice. The approach is based on the noninvasive technique of gamma camera sdntigraphy and takes advantage of previous observations12'13 that radiolabeled LDL is rapidly focally sequestered in abnormal arterial wall. The earlier observations were confirmed and extended in the present study, which showed that some human atherosclerotic lesions in the carotid, iliac, and femoral circulations could be imaged externally with the gamma scintillation camera after injection of T c - L D L . Based on the data obtained from carotid endarterectomy specimens, lesion composition may have determined whether " T c - L D L accumulation was quantitatively sufficient to produce an external image. The carotid plaque that did image was made up of tissue that could be described as being in a state of active evolution; it had abundant foam cells and macrophages as well as an area of poorly organized intramural hemorrhage. The total accumulation of radiolabel by this specimen was far greater than that of any other specimen. Conversely, the five fibrocalcific carotid plaques that did not image were made up of tissue which could be described as quiescent, or "burned-out." However, regardless of whether they imaged, all five specimens that could be subdivided had greater radioactivity In the centers of plaques and less radioactivity elsewhere. These findings support the concept that the atherosclerotic process pro- IMAGING HUMAN ATHEROSCLEROSIS Table 3. Relative Radioactivity and Histology of Carotid Endarterectomy Patient no. 3 4 7 8 10 Downloaded from http://atvb.ahajournals.org/ by guest on May 14, 2017 14 Specimen Center of plaque, anterior Center of plaque, posterior Edge of plaque Center of plaque, distal Center of plaque, proximal External carotid Entire specimen Plaque, proximal Center of plaque, posterior Center of plaque, anterior Plaque, distal External carotid Center of plaque, anterior Center of plaque, posterior Edge of plaque, anterior Edge of plaque, posterior Center of plaque Edge of plaque External carotid Relative radioactivity* 1.00 0.92 0.27 1.00 0.89 0.55 — 1.00 1.00 0.68 0.63 0.47 1.00 0.53 0.57 0.39 1.00 0.55 0.47 Histologyt Category A Category A Intermediate Category B Category B Category B Category B Intermediate Category B Intermediate Category B Category B Category A Category A Category B Intermediate Category B Category B Intermediate T h e relative radioactivity was calculated for each patient's specimen by dividing the cpm/gm of each piece of specimen by the cpm/gm of the most radioactive piece from that patient. tCategory A. Abundant macrophages and foam cells and hematoma or necrosis. Category B. Mature fibrous connective tissue with or without areas of calcification. Intermediate, sparsely cellular, fibrocalcrfic, only small regions similar to Category A. duces specific local tissue changes that might be used to locate plaques by external imaging if suitable radiopharmaceuticals were available. In this study, which employed T c - L D L as the radiopharmaceutical, extracellular matrix produced by cells present in plaques may have mediated, at least in part, the focal accumulation of radiolabeled LDL. For example, the quantity and type of glycosaminoglycans,18 which are known to bind LDL, may be important. Whatever the specific tissue components that may be involved in radiolabel accumulation, the results of this study suggest that the ability to image atherosclerotic plaque is dependent in some way on tissue composition. Thus, the composition of lesions may be at least partially elucidated by external imaging. Based on the evidence from earlier studies 141920 and from the data presented here, we hypothesize that if a lesion images with " T c - L D L , it is likely to be actively evolving. In recent years, emphasis has been placed on the importance of acute rupture or fissure in chronic coronary arterial atherosclerotic plaques as the critical event precipitating varying degrees of occlusion by thrombus, which, in turn, results in cardiac symptoms ranging from unstable angina to infarction to sudden death.7 It seems likely that quiescent, mature fibrocalcific plaques would be least likely to rupture, while softer lesions with a cellular, hemorrhagic, or necrotic core would be more likely to undergo acute plaque change. Further studies will be needed to confirm the possibility that an appropriate radiopharmaceutical could be used to detect such evolving plaques by external imaging. Lees et al. 469 In addition to the specific tissue characteristics of plaques, a major determinant of the ability to image with the gamma camera is the relationship between the radioactivity in the lesion and that in the blood pool, known as the target-to-background ratio. In this study, the target-tobackground ratio obtained with T c - L D L was clearly not optimal, perhaps because the biological half-life of LDL in the plasma ranges from 2 to 6 days, while the physical half-life of T c is only 6 hours. This led to uncertainty in the interpretation of focal cardiac radiolabel accumulation in four patients, and, in light of the focal accumulation of radiolabel measured ex vivo in the carotid endarterectomy specimens, could well have led to negative imaging studies in the presence of active disease. We are now investigating a variety of ways to improve the target-to-background ratio of the imaging radiopharmaceutical. Although a method of attaching to LDL an imaging isotope with a half-life longer than the 6 hours of T c is not yet available, this is one possible approach. However, " " T c does have the advantage of being readily available and inexpensive, and it appears to be partially trapped intracellularly, as indicated by the 24-hour urinary excretion of radiolabel, which ranged only from 4% to 12%; this finding, in contrast to results obtained with 12SI-LDL21 where 20% to 50% of the isotope appeared in the urine in 24 hours, was consistent with animal data obtained previously,1419-20 and suggested that the " T c that enters cells bound to protein may be trapped to a considerable extent in tissue, as has been demonstrated for certain radiolabeled conjugates of LDL.22 Another approach would be to develop an agent that would be cleared more rapidly from plasma while being retained in atherosclerotic plaques. Whatever radiopharmaceuticals prove to be optimal, the present study demonstrates that external imaging of human atherosclerosis is feasible and may aid in differentiating quiescent from actively evolving plaques. Acknowledgments The authors thank Martha Barlai-Kovach, Frances Keech, Helen Shing, and Sara Murray for their expert technical assistance and Samuel W. Stein for helpful discussions. This work would not have been possible without the collaboration of the physicians and surgeons of the Massachusetts General and New England Deaconess Hospitals, particularly Herman K. Gold, Robert C. Leinbach, Robert G. Ojemann, and Gary W. Gibbons. References 1. Bernstein EF, Humber PB, Collins QM, Dilley RB, Devln JB, Stuart SH. Life expectancy and late stroke following carotid endarterectomy. Ann Surg 1983;198:80-86 2. CASS Study Group. Coronary Artery Surgery Study (CASS): A randomized trial of coronary artery bypass surgery. Survival data. Circulation 1983:68:939-950 3. Gruntzlg AR. Results from coronary angioplasty and implications for the future. Am Heart J 1982;103:779-783 4. Van de Werf F, Ludbrook PA, Bergmann SR, et al. Coronary thrombolysis with tissue-type plasminogen activator in patients with evolving myocardial Infarction. N Engl J Med 1984:310:609-613 5. Nlkklla EA, Vliklnkoskl P, Valla M. Effect of lipid-lowering treatment on progression of coronary atherosclerosis. Circulation 1983;68(suppl 3):188 6. Llpld Research Clinics Program. The UpkJ Research Clinics Coronary Primary Prevention Trial Results: I Reduc- 470 Downloaded from http://atvb.ahajournals.org/ by guest on May 14, 2017 7. 8. 9. 10. 11. 12. 13. 14. ARTERIOSCLEROSIS VOL 8, No 5, SEPTEMBER/OCTOBER 1988 tion in incidence of coronary heart disease. II The relationships of reduction in incidence of coronary heart disease to cholesterol lowering. JAMA 1984;251:351-364, 365-374 Davles MJ, Thomas AC. Plaque Assuring—the cause of acute myocardial infarction, sudden ischaemlc death, and crescendo angina. Br Heart J 1985;53:363-373 Hoff HF. Apoprotein localization in human cranial arteries, coronary arteries, and the aorta. Stroke 1976;7:390-393 Smith EB, Staples EM, Dletz HS, Smith RH. Role of endothelium in sequestration of lipoprotein and fibrinogen in aortic lesions, thrombi, and graft pseudo-intimas. Lancet 1979;2:812-816 Honlg M, Shalnoff JR, Lowy AD Jr. Flotational lipoproteins extracted from human atherosclerotic aortas. Science 1956; 124:176-178 Gero D, Gergely J, Jakab L, Szekety J, Vlrag S. Comparative Immunoelectrophoretjc studies on homogenates of aorta, pulmonary arteries and inferior vena cava of atherosclerotic individuals. J Atherosclerosis Res 1961;1:88-91 Roberts AB, Lees AM, Lees RS, et al. Selective accumulation of low density lipoproteins in damaged arterial wall. J Lipid Res 1983:24:1160-1167 Lees RS, Lees AM, Strauss HW. External imaging of human atherosclerosis. J Nucl Med 198324:154-156 Lees RS, Garabedlan HD, Lees AM, et al. Technetium-99m low density lipoproteins: preparation and biodistribution. J Nucl Med 198526:1056-1062 Index Terms: human atherosclerosis • 15. Hatch FT, Lees RS. Practical methods for plasma lipoprotein analysis. Adv LJpid Res 1968;6:1-68 16. PrttmanRC,CarewTE,AttleAD,WttzumJL,WatanabeY, Steinberg D. Receptor-dependent and receptor-independent degradation of low-density lipoprotein in normal rabbits and in receptor-deflcierrt mutant rabbits. J Biol Chem 1982; 257:7994-8000 17. Spady DK, Bllhelmer DW, Dletschy JM. Rates of receptordependent and independent low density lipoprotein uptake in the hamster. Proc Nati Acad Sd USA 1983;80:3499-3503 18. Wight TN, Curwen KO, Lltrenta MM, Alonso DR, Mlnlck CR. Effect of endothelium on glycosamirtoglycan accumulation in injured rabbit aorta. Am J Pathol 1983;113:156-164 19. Isaacsohn JL, Lees AM, Lees RS, Strauss HW, BarlaiKovach M, Moore TJ. Adrenal imaging with technetium99m-labelled tow density lipoproteins. Metabolism 1986; 35:364-366 20. Flschman AJ, Lees AM, Lees RS, Barlal-Kovach M, Strauss HW. Accumulation of native and methylated low density lipoproteins by healing rabbit arterial wall. Arteriosclerosis 1987;7:361-366 21. Brook JQ, Torsvlk H, Lees RS, McCluskey MA, Feldman HA. Low density lipoprotein metabolism in Type IV and Type V hyperiipoproteinemia. Metabolism 1979;28:4-8 22. Plttman RC, Carew TE, Glass CK, Green SR, Taylor CA Jr, Attle AD. A radioiodinated, intracellulariy trapped Ikjand for determining the sites of plasma protein degradation in vivo. Biochem J 1983;212:791-800 gamma camera imaging • bw density lipoproteins • technetium labeling Imaging human atherosclerosis with 99mTc-labeled low density lipoproteins. A M Lees, R S Lees, F J Schoen, J L Isaacsohn, A J Fischman, K A McKusick and H W Strauss Downloaded from http://atvb.ahajournals.org/ by guest on May 14, 2017 Arterioscler Thromb Vasc Biol. 1988;8:461-470 doi: 10.1161/01.ATV.8.5.461 Arteriosclerosis, Thrombosis, and Vascular Biology is published by the American Heart Association, 7272 Greenville Avenue, Dallas, TX 75231 Copyright © 1988 American Heart Association, Inc. All rights reserved. Print ISSN: 1079-5642. Online ISSN: 1524-4636 The online version of this article, along with updated information and services, is located on the World Wide Web at: http://atvb.ahajournals.org/content/8/5/461 Permissions: Requests for permissions to reproduce figures, tables, or portions of articles originally published in Arteriosclerosis, Thrombosis, and Vascular Biology can be obtained via RightsLink, a service of the Copyright Clearance Center, not the Editorial Office. 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