Thallium 201 muscle scintigraphy: application to the management of patients with arterial occlusive disease

Usefulness of thallium-201 muscle scan to investigate perfusion reserve in the lower limbs of patients with systemic lupus erythematusus

Patients with systemic lupus erythematosus (SLE) may develop premature atherosclerosis, notably peripheral vascular disease presenting with intermittent claudication or gangrene. This study evaluates the usefulness of thallium-201 muscle perfusion scan (Tl-201 muscle scan) for investigating perfusion reserve in the lower limbs of 25 asymptomatic, female SLE patients without peripheral ischemia findings. The patients showed no evidence of peripheral arterial disease in history, physical examination, or Doppler ultrasonography. A control group consisted of 24 healthy, age-matched women. Each subject flexed her right foot maximally both dorsally and plantarly 60 times. In the middle of this exercise, 2 mCi of Tl-201 was injected intravenously. Three minutes after the injection, a posterior image of both calves was obtained using a gamma camera. Rectangular regions of interest were symmetrically drawn over both calves. The total count in the resting calf was subtracted from the total count in the exercising calf, and the percentage of increase, termed the perfusion reserve, was determined. A significant difference was found between the perfusion reserves of the SLE patients and control groups (75.3+/-8.9% and 99.6+/-9.0%, respectively, P <0.05). In conclusion, perfusion reserve in the lower limb muscles of SLE patients may be measured by Tl-201 muscle perfusion scan.

Usefulness of thallium-201 muscle perfusion scan to investigate perfusion reserve in the lower limbs of Type 2 diabetic patients

This study evaluated the usefulness of thallium-201 muscle perfusion scan (Tl-201 muscle scan) to investigate perfusion reserve in the lower limbs of asymptomatic Type 2 diabetic patients without peripheral ischemia findings. Tl-201 muscle scan was carried out in 36 diabetic male patients with Type 2 diabetes mellitus of more than 10 years in duration who had no evidence of peripheral arterial disease in their history, physical examination, or Doppler ultrasonography. A control group consisted of 24 healthy age-matched nondiabetic men. Each subject flexed their right foot maximally both dorsally and plantar 60 times. In the middle of this exercise, 2mCi Tl-201 was injected intravenously. Three minutes after the injection, a posterior image of both calves was obtained using a gamma camera. Rectangular regions of interest (ROIs) were symmetrically drawn over both calves. The total count (Ct) in the resting calf was subtracted from the Ct in the exercising calf, and the percentage increase, termed the perfusion reserve, was determined. A significant difference was found between the perfusion reserves of the Type 2 diabetic patients and control groups (70.2+/-10.7% and 98.6+/-9.4%, respectively; P<.05). In conclusion, the perfusion reserve in the lower limb muscles in Type 2 diabetic patients may be measured by Tl-201 muscle perfusion scan.

Lower-limb vascularization in diabetic patients. Assessment by thallium-201 scanning coupled with exercise myocardial scintigraphy

OBJECTIVE

To investigate, by thallium-201 scanning, circulation in the muscles of the lower limb (LL) in diabetic patients without clinical peripheral vascular disease but with a high cardiovascular risk profile.

RESEARCH DESIGN AND METHODS

A total of 80 diabetic patients (76 patients with type 2 diabetes, mean age 57.3 years, duration of diabetes 13.0 +/- 7.5 years) with more than one additional cardiovascular risk factor but no claudication were investigated. After stress testing, 1.5 MBq/kg thallium-201 was administered to perform myocardial single-photon emission computed tomography followed by LL scanning. Muscle blood flow was considered abnormal if the asymmetry in thallium-201 uptake between the two buttocks and/or thighs and/or calves was > 10%.

RESULTS

Muscle perfusion defects were found in 42% of the patients, mainly in the calves. These defects correlated with retinopathy (P = 0.042) and the HbA1c level (P = 0.044). In patients with defects in the buttock and/or thigh, the prevalence of nephropathy and retinopathy was higher than in those with isolated defects in the calf (P = 0.032 and 0.023, respectively).

CONCLUSIONS

This study suggests that LL scanning coupled with myocardial scintigraphy is a convenient method of investigating peripheral muscle circulation. Proximal perfusion defects in patients without clinical arterial disease are associated with increased prevalence of retinopathy and nephropathy and, therefore, may be due to microvascular disease of LL muscle. Distal defects may indicate silent macrovascular disease of the LL.

Assessment of peripheral arterial vascular disease with radionuclide techniques

Various radioisotopic imaging techniques for noninvasive detection of vessel stenosis and for functional investigation of reduced blood flow and follow-up have been developed during the last decade in peripheral vascular disease (PVD), with the aim of replacing invasive techniques and complementing standardized methods. Radionuclide assessment of PVD is divided into 2 major groups: imaging of perfusion and metabolic investigations. The measurement of arterial blood flow and muscle perfusion is intended to show the morphology, to evaluate the functional consequences of PVD, and to quantify the latter. The application of radiolabeled tracers was developed as a noninvasive alternative to angiography in morphologic imaging. Treadmill testing has been used to assess the functional effects of reduced blood flow in PVD where the onset of pain indicates the stage of disease, but the results can be confused by other symptoms. Scintigraphic measurement of muscle perfusion should detect insufficient nutritional blood flow in peripheral muscle and thus have a higher specificity for PVD than treadmill testing alone. Although there are very promising theoretical and experimental data in animals, the clinical use of radionuclide investigations is limited by different technical problems, such as methodologic differentiation between skin and muscle perfusion, the lack of controlled and prospective studies, and incomplete correlation with other standardized routine techniques. Among the great number of radioisotopic metabolic imaging techniques, only radiolabeled platelets and lipoproteins, to some extent, have shown a limited potential clinical use. Some other approaches seem to have a high potential from a theoretical point of view. They are limited, however, by a great number of problems. Correlation with sonographic or magnetic resonance imaging (MRI) findings may identify a potential metabolic value. Correlation with angiography reflecting the extent of the disease makes no sense. So far with PVD, neither radioisotopic perfusion studies nor metabolic imaging techniques are able to achieve a level of routine application or wider meaningful interpretation of the clinical condition of a specific patient. Competing techniques are easier to perform, less expensive, faster, more widely available, and do not carry the radiation burden. Positron emission tomography is still in its early stages of application, with great theoretical potential but at a high price. A great deal of work is still required to transform in vitro and experimental experience into more meaningful routine radioisotopic investigations in patients with PVD.

Investigation of perfusion reserve using 99Tc(m)-MIBI in the lower limbs of diabetic patients

This study aimed to investigate the microvascular pathology in the lower limbs of diabetic patients without symptoms or findings of peripheral ischaemia by measuring perfusion reserve scintigraphically. It was carried out in 47 female subjects who had no evidence of peripheral arterial disease in their history, physical examination or Doppler ultrasonography. The diabetic group consisted of 25 women (mean age 54.2 +/- 3.54 years) with type II diabetes mellitus of more than 10 years' duration. A control group consisted of 22 healthy non-diabetic women (mean age 50.14 +/- 6.75 years). Each subject flexed their right foot maximally both dorsally and plantar 60 times. In the middle of this exercise, 370 MBq technetium-99m-methoxyisobutylisonitrile (99Tc(m)-MIBI) was injected intravenously. Ten minutes after the injection, a posterior image of both calves was obtained using a gamma camera. Rectangular regions of interest were symmetrically drawn over both calves. The total count in the resting calf was subtracted from the total count in the exercising calf, and the percentage increase, termed the perfusion reserve, was determined. A significant difference was found between the perfusion reserves of the diabetic and control groups (76.04 +/- 12.96% and 95.91 +/- 12.83%, respectively; P<0.001). In conclusion, microvascular pathology may be determined scintigraphically by measuring the perfusion reserve in the lower limb muscles in diabetic patients. This method may also be used to evaluate perfusion abnormalities in other circulatory disorders.

Whole-body exercise thallium imaging in smokers

Whole-body exercise thallium imaging (WBEI) can show abnormalities of leg muscle perfusion in patients with symptomatic peripheral artery disease (PAD). This study compared the exercise distribution of thallium-201 at different levels of the legs in asymptomatic smokers and non-smokers who performed a maximal graded treadmill test. A group of 74 smokers (more than 20 pack-years) with (n = 51) or without coronary artery disease (CAD) (n = 23) were included in group 1 and 64 non-smokers with a low probability of PAD and CAD in group 2. Patients in group 1 were older than the patients in group 2 (58 +/- 9 versus 48 +/- 12 years, p < 0.0001). Indexes of asymmetry were significantly higher in group 1, at each level of the legs, both in anterior and posterior views (0.001 < p < 0.05), except at thigh level in anterior view. Fractional uptake indexes of thallium-201 were significantly lower in group 1 than in group 2 at calf level (p = 0.0001 in anterior and posterior views) and buttocks (p = 0.006 and p = 0.009 in anterior view only). Interextremity asymmetry was four to six times more frequent at calf level in smokers than in non-smokers. These WBEI abnormalities in smokers are highly suggestive of silent PAD or at least decreased vascular reactivity in clinically uninvolved vessels.

The quantitation of blood flow/metabolism coupling at rest and after exercise in peripheral arterial insufficiency, using PET and 15-0 labeled tracers

Regional blood flow and oxygen uptake of the lower limbs were studied in 11 patients with arterial insufficiency (10 with severe unilateral, 1 with bilateral intermittent claudication). Regional muscle blood flow (F), oxygen consumption rate (R), and oxygen extraction fraction (E) were evaluated by positron emission tomography (PET) and bolus inhalation of C15O2 and 15O2 by the patient. Tomograms were recorded at the greatest diameter of legs, at rest and ten minutes after a treadmill walk test leading to the development of ischemic pain in the affected leg. In 5 patients, F and E were correlated with the results of occlusive venous strain gauge plethysmography and with the measurements of blood gases in one brachial artery and in the femoral vein of the affected limb. Blood flow values measured at rest and after exercise by PET were poorly correlated with the plethysmographic findings. This may be because PET does not interfere with flow as venous occlusion plethysmography does in low peripheral pressure conditions. The results show that F, R, and E were not significantly different in normal and pathologic legs at rest. The values of F and R were significantly higher in pathologic than in normal lower limbs, ten minutes after exercise, whereas E was not significantly altered by exercise at any side. This suggests that, during the recovery from a walk test, the delayed increase in oxygen uptake is proportional to the delayed hyperemia in the ischemic muscles ("oxygen debt") and probably not linked to a luxury perfusion.

Comparison of whole-body thallium imaging with transcutaneous PO2 in studying regional blood supply in patients with peripheral arterial occlusive disease

Quantitatively estimating functional reserve of blood supply to the legs in patients with peripheral arterial occlusive disease (PAOD) remains a clinical issue. This study was designed to investigate the regional blood supply to the legs in PAOD patients during exercise by use of thallium 201 (201Tl) whole-body imaging in comparison with transcutaneous PO2 (tcPO2) measurement. Thirty-three patients with PAOD and 10 subjects without PAOD (control) performed an incremental cycle ergometry (CE), while tcPO2 was continuously registered on the involved calf. In the last minute of exercise, 2 mCi of 201Tl was injected intravenously and the 201Tl whole-body images were taken immediately (stress) and four hours (redistribution) following stress with a dual-head camera system. Regional blood supply (RBS) (%) was calculated from the geometric mean counts of the region of interest divided by the total counts of the whole body. The performance of PAOD patients was reduced in doing CE, and tcPO2 fell distinctly in PAOD patients (from 51 to 19 mmHg) whereas it increased in controls (from 57 to 67 mmHg). The RBS in PAOD patients was obviously reduced in comparison with that of controls. While in controls the RBS of the calf (3.1%) at stress did not differ from that at redistribution (3.4%), in PAOD patients the redistribution RBS (2.8%) increased as compared with that of stress (1.5%). There was a hyperbolic relationship between stress RBS of the calf and the velocity of tcPO2 fall in PAOD patients during exercise test (velocity of tcPO2 fall = -0.032 + 0.39/RBS, r2 = 0.54, P < 0.05). In conclusion, the RBS determined by 201Tl whole-body imaging is comparable to the tcPO2 measurement in differentiating patients with PAOD from subjects without PAOD during exercise. Regional 201Tl uptake reflects regional blood supply in PAOD patients. There is a hyperbolic relationship between the RBS derived from 201Tl whole-body imaging and tcPO2 in PAOD patients during exercise, implying that in a critical ischemia the lower the RBS is, the more steeply the tcPO2 decreases.

Technetium-99m sestamibi scintigraphy for the assessment of lower extremity ischaemia in peripheral arterial disease

Technetium-99m sestamibi was used for functional investigation of the muscle perfusion of lower extremities in 35 patients with peripheral vascular disease. The aim was to test what useful information could be obtained by additional imaging of the legs in patients referred for risk stratification with dipyridamole myocardial scanning. Posterior images were acquired over the thighs and calves after postocclusive reactive hyperaemia and at rest. Inter- and intraextremity ratios and differences between the stress and rest data were used for the assessment of abnormal circulation. Arteriography was performed in every case, and surgical procedures or transluminal angioplasty in 31 patients. To estimate diagnostic accuracy, the results of 99mTc-sestamibi scintigraphy were compared with those of angiography and the functional consequences of revascularization procedures. The sensitivity and specificity of 99mTc-sestamibi scintigraphy were 55% and 25%, respectively, with an overall accuracy of 50%. Apparently methodological error was not responsible for these poor results. Instead, a paradoxically high uptake of the radiopharmaceutical in muscles supplied by significantly stenosed vessels was identified as the main source of both false-negative and false-positive results. The phenomenon resembles the findings of a previous study involving delayed administration of thallium-201 after exercise. In conclusion, 99mTc-sestamibi scintigraphy has not proved sufficiently reliable to help in the management strategy for patients with peripheral vascular disease.

Whole-body thallium imaging in coronary artery disease

The aim of this study was to evaluate the incidence, type, and severity of asymptomatic leg perfusion abnormalities in 116 male patients with proven coronary artery disease (CAD) who performed near-maximal treadmill test. Interextremity asymmetry was observed in 60% of patients, but the incidence of this sign increased with age (from 35% below forty-five years of age to 72% over sixty-one years). Asymmetry was very marked or marked in 61% of all segments and moderate in 39% of them. A significant decrease in fractional uptake was observed in 21% of patients with CAD and in 25% of those with interextremity asymmetry. Myocardial ischemia, which was defined by reversible defects on myocardial tomoscintigraphy, was three times more frequent in patients with interextremity asymmetry than in patients with normal results from exercise whole-body thallium scintigraphy. This observation, combined with type, extent, and location of asymmetry, is highly suggestive of silent peripheral arterial disease in most cases. Whole-body scan could easily be performed following an exercise myocardial thallium scan so as to provide information on multifocal atherosclerosis in patients with CAD or multiple and severe vascular risk factors. The prognostic value of these silent peripheral muscle perfusion abnormalities remains to be established.

Evaluation of leg perfusion during exercise using technetium 99m sestamibi. A new test for peripheral vascular disease

Thirty patients with occlusive peripheral vascular disease underwent clinical examination, segmental blood pressure determinations, intra-arterial digital subtraction angiography, and treadmill stress testing with injection of technetium 99m sestamibi at peak exercise. Radionuclide images of the thighs, calves, and feet showed clear delineation of major muscle groups. Diminished radiotracer distribution was closely correlated with the presence of occlusive vascular disease on angiography and with the presence of claudication and reduced segmental blood pressure. A quantitative scheme based on pixel intensity was developed to compare areas of regional perfusion.