201Tl Single Photon Emission Tomography Research Articles

Postoperative residual tumour imaged by contrast-enhanced computed tomography and 201Tl single photon emission tomography: can they predict progression-free survival in high-grade gliomas?

To evaluate if postoperative residual tumour imaged by either computed tomography or 201Tl single photon emission tomography (SPECT) carried out postoperatively could predict progression-free survival (PFS) in high-grade malignant gliomas. Thirty-three patients with high-grade malignant gliomas underwent both contrast-enhanced CT scan and 201Tl-SPECT postoperatively before receiving radiotherapy. The PFS was evaluated against the individual reports of the above two imaging studies by univariate analysis. CT and 201Tl-SPECT were carried out within a median interval of 17 days after surgery. Of the 33 patients, CT and 201Tl-SPECT were reported as positive for residual tumours in 23 (69.7%) and 30 (91%) patients, respectively. Sensitivity, specificity and overall accuracy were 71.4%, 40% and 66.6% for CT, and 96.4%, 40% and 87.8% for 201Tl-SPECT, respectively, and were based on their last follow-up status (P = 0.627 for CT; P = 0.053 for 201Tl-SPECT). The median PFS for patients reported to be positive or negative on CT scan was 4 and 5 months, respectively (P = 0.202). With 201Tl-SPECT, although the median PFS for patients with a positive 201Tl uptake was also 4 months, it had not even reached for those reported having a negative 201Tl uptake (cumulative survival 66.7% at last follow-up) (P = 0.198). However, Karnofsky performance status (KPS) was the only significant predictor on univariate analysis (KPS: < 80 vs. > or = 80; P < 0.001) for PFS. Although both the imaging modalities have a poor specificity, postoperative 201Tl-SPECT had a significantly better accuracy to predict the status at last follow-up than contrast-enhanced CT. Nevertheless, KPS remained the most significant outcome predictor for PFS in high-grade malignant gliomas.

Use of 201Tl SPECT imaging to assess the response to therapy in patients with high grade gliomas.

To assess the potential role of 201Tl single photon emission tomography (201-Thallium SPECT) when compared to other imaging modalities in the evaluation of the response to therapy in high grade gliomas. Twenty patients with histologically proved high grade glioma have been included: 15 with glioblastoma (GBM), 3 with anaplastic astrocytoma (AA) and 2 with anaplastic oligoastrocytoma (AOA). Patients were assessed by 201Tl SPECT, computed tomography (CT) and magnetic resonance imaging (MRI) at (a) either at the moment of maximum response to first line chemotherapy, or after the completion of radiotherapy and chemotherapy if post-surgical residual disease was present, and (b) after the completion of second line chemotherapy if disease persisted, or either a relapse or disease progression was confirmed. Final response was evaluated according to the McDonald criteria, and by comparing SPECT, CT and MRI results. According to the McDonald criteria, clinical response after first line chemotherapy was 5 partial response, 7 stable disease and 8 progressive disease. Evaluation by 201Tl SPECT was in agreement with such criteria in nearly all patients (90%). MRI findings closely agreed with the clinical follow-up. CT findings clearly differed from those observed by SPECT and MRI. After second line therapy, 10 patients progressed, 3 had stable disease and 7 had partial response. 201Tl SPECT agreed with the clinical status in 89% cases, whereas MRI and, specially CT, fared significantly lower. Compared to conventional neuroimaging, 201Tl SPECT added valuable information in the assessment of the response to therapy in our patient population; whenever findings were not conclusive and in the case of disagreement between CT and MRI findings.

Diagnostic accuracy of low-dose dobutamine echocardiography in predicting post-revascularisation recovery of function in patients with chronic coronary artery disease: relationship to thallium-201 uptake.

It is known that contractile reserve may be blunted if perfusion and coronary flow reserve are reduced. Thus, it is conceivable that the predictive accuracy of dobutamine echocardiography may differ according to perfusion tracer uptake. The aim of this study was therefore to assess the relationship between the level of thallium-201 uptake and the accuracy of dobutamine echocardiography in identifying reversible dysfunction. Sixty-nine patients (age 59+/-8 years, ejection fraction 40%+/-11%) with chronic coronary artery disease scheduled for coronary revascularisation were studied. All patients underwent rest 201Tl single-photon emission tomography and two-dimensional echocardiography at rest and during low-dose dobutamine infusion on the same day before revascularisation and repeated echocardiography at least 30 days thereafter. At follow-up, recovery of function was observed in 49% of 339 dysfunctional segments. The percentage of segments with post-revascularisation recovery of function and the percentage with contractile reserve increased in parallel with 201Tl uptake both in the total group of segments (chi2=35.5, P<0.0001 and chi2=35.9, P<0.0001, respectively) and among the 183 akinetic segments (chi2=44.4, P<0.0001 and chi2=14.6, P<0.05, respectively). The dysfunctional segments were divided into three groups according to 201Tl uptake: (a) uptake <65%, (b) uptake between 65% and 79%, (c) uptake >80%. The positive predictive value increased significantly with the level of 201Tl uptake, and was suboptimal (46%) in akinetic segments with severely reduced 201Tl uptake. The negative predictive value decreased significantly with 201Tl uptake, and it was less than suboptimal (29%) in akinetic segments with normal tracer uptake. Sensitivity was lower in the subset of akinetic segments (42%-63%) than in all dyssynergic segments (63%-76%), whereas specificity was very high in akinetic segments (80%-84%). It is concluded that the accuracy of low-dose dobutamine echocardiography in predicting reversibility of regional dysfunction varies considerably according to 201Tl uptake at rest and to the severity of regional dysfunction.

Increased uptake of 99Tcm-ethyl cysteinate dimer in patients with brain tumours.

We performed 229 99Tcm-ethyl cysteinate dimer (ECD) single photon emission tomography (SPET) studies in 185 patients with brain tumour. Increased uptake of the tracer was observed in 11 cases. In six of these 11 patients, focal intense activity was seen in the area surrounding the tumour. Five of these six patients had episodes of seizure, and ictal SPET showed further increased uptake in the area of hyperperfusion in one patient. Hyperperfusion surrounding the tumour might be related to seizure. In the remaining five patients, increased accumulation was seen in the tumour. Three of these five patients had a discrepancy between 99Tcm-ECD SPET and 201Tl SPET imaging. There could be some difference in the mechanism of accumulation in the tumour between 99Tcm-ECD and 201Tl.

The value of gallium-67 and thallium-201 whole-body and single-photon emission tomography images in dialysis-related beta 2-microglobulin amyloid.

The aim of this study was to investigate the value of gallium-67 and thallium-201 whole-body and single-photon emission tomography (SPET) images in long-term dialysis patients in whom dialysis-related beta 2-microglobulin amyloid (beta 2-MA) was clinically suspected. Twenty-three patients who had received dialysis for at least 10 years were included in the study. A technetium-99m methylene diphosphonate (MDP) whole-body scan was performed in all of the patients. If there was any MDP accumulation in the articular and/or peri-articular region, 67Ga and 201Tl whole-body and SPET images were then acquired. If any 67Ga and/or 201Tl uptake was observed, a CT-guided biopsy was done. In those patients who had articular and/or peri-articular uptake of 99mTc MDP, 67Ga and/or 201Tl and who were pathologically proven to have beta 2-MA, 99mTc MDP, 67Ga and 201Tl whole-body scans and SPET were carried out again, both 3 months and 1 year after initiation of treatment. This served to evaluate the therapeutic effect and allowed comparison with the clinical findings. Of the 23 patients, eight had abnormal 99mTc MDP uptake. Among these eight, six had intense 99mTc MDP, 67Ga and 201Tl uptake in the articular and peri-articular regions before medication. Three months after the start of treatment, there were very marked decreases in uptake on both the 67Ga and 201Tl scans but less obvious changes in uptake of 99mTc-MDP. In comparison with the other clinical manifestations such as limitation in range of motion, the more the painful disability improved, the less was the uptake on both 67Ga and 201Tl scans. There were virtually no differences in uptake pattern between the three scans of each radiopharmaceutical obtained for each patient in both 3 months and 1 year after initial of treatment. It is concluded that 99mTc-MDP whole-body bone scan can both detect active and pre-existing inactive deposits of beta 2-MA. 67Ga and 201Tl scans are helpful to differentiate active from inactive deposits of beta 2-MA and to evaluate the therapeutic effect on these patients. SPET images are usually needed to distinguish articular and periarticular lesions from bone lesions.

201Tl SPET in the differential diagnosis of brain tumours.

The aims of this study were to assess the utility of 201Tl single photon emission tomography (SPET) in the differential diagnosis of brain tumours and to elucidate the relationship between 201Tl tumour uptake and degree of contrast-enhancement on magnetic resonance imaging (MRI). Early (15 min) and delayed (3 h) 201Tl SPET imaging and T1-weighted MRI were performed before and after Gd-DTPA enhancement in 101 (41 malignant and 60 benign) untreated brain tumours. The 201Tl uptake ratio (tumour-to-normal brain count ratio) for both the early and delayed SPET studies and the retention index (the ratio of delayed to early 201Tl uptake) were calculated. Malignant tumours were separated from benign tumours with 87% accuracy based on the assumption that tumours with a 201Tl retention index < 0.7 or no abnormal uptake are benign. Meningiomas and pituitary adenomas were differentiated from other benign tumours by their characteristic pattern on SPET. The degree of contrast-enhancement of the tumour on MRI was concordant with the early 201Tl uptake ratio for most histological types. However, schwannomas and cavernous haemangiomas showed a low 201Tl uptake ratio in spite of a high degree of contrast-enhancement on MRI. In conclusion, 201Tl SPET provides additional information that helps in the differential diagnosis of brain tumours.

Thallium-201 right lung/heart ratio during exercise in patients with coronary artery disease: relation to thallium-201 myocardial single-photon emission tomography, rest and exercise left ventricular function and coronary angiography.

The aim of this study was to correlate lung thallium-201 uptake on exercise with 201Tl single-photon emission tomography (SPET) myocardial perfusion imaging, rest and exercise equilibrium radionuclide angiographic and coronary angiographic findings in patients with coronary artery disease (CAD) using a simple, reproducible lung/heart (L/H) ratio that would be easy to use in clinical practice. L/H ratio was defined on the anterior planar image obtained during exercise 201Tl SPET acquisition as the mean counts per pixel in an entire right lung field region of interest divided by the mean counts per pixel in the hottest myocardial wall region of interest. We studied 103 patients. Fifty-nine patients (group I) with <5% likelihood of CAD were used as a reference group. In 44 CAD patients (group II), L/H ratio was compared with 201Tl SPET, radionuclide angiographic and coronary angiographic variables. The group I L/H ratio of 0.35+/-0.05 (mean +/-1 SD) was significantly lower (P<0.001) than the group II L/H ratio of 0. 45+/-0.10. An L/H ratio >0.45 (mean + 2 SD in group I) was considered abnormal. In group II, L/H ratio showed a significant correlation with stress and rest 201Tl perfusion defect size (r = 0. 39 and r = 0.42, P<0.01, respectively), but not with extent of ischaemic myocardium. The mean L/H ratio was 0.41+/-0.10 in patients with one-vessel disease (n = 15), 0.46+/-0.08 in those with two-vessel disease (n = 17) and 0.47+/-0.12 in those with three-vessel disease (n = 12), but no significant difference was found between the three subgroups. L/H ratio showed a significant inverse relation with rest and exercise left ventricular ejection fraction (r = -0.37 and r = -0.50, P<0.05 and P<0.001, respectively). Using stepwise multiple regression analysis, exercise left ventricular ejection fraction and previous history of hypertension were the sole two variables independently predictive of the L/H ratio. In conclusion, although lung thallium uptake is usually found to correlate with extent and severity of CAD, increased L/H ratio should primarily be considered as a marker of exercise-induced left ventricular systolic and perhaps diastolic dysfunction, probably independent of the underlying cardiac disease.

Reverse redistribution on thallium-201 single-photon emission tomography after primary angioplasty: a one-year follow-up study.

The prognostic significance of reverse redistribution (RR) on thallium-201 single-photon emission tomography (SPET) images after acute myocardial infarction (AMI) has not been studied in detail. Moreover, RR data in patients treated with primary angioplasty are lacking. Fifty consecutive patients (including 40 men with a mean age of 54+/-11 years) with a first AMI were treated with primary angioplasty and followed up for 13+/-5 months for the following end-points: death, reinfarction and recurrent angina requiring revascularisation. Admission and peak creatine kinase myocardial enzyme (CKMB) and ejection fraction (EF) at discharge were studied as markers of myocardial damage. Thallium-201 stress-redistribution SPET studies at 1 month were analysed using a 13-segment, 4-point scoring system. Segments showing a worsening of perfusion by at least 1 point on redistribution studies were defined as showing RR. RR was present in 13 (26%) patients (group 1) and absent in 37 (74%) (group 2). Both groups were comparable for age, sex, peak CKMB release, EF and Q-wave myocardial infarctions. TIMI flow 3 was obtained in 92% in group 1 and 95% in group 2 (P = 0.95). On admission, CKMB was significantly lower in group 1 (18+/-14 vs 44+/-41 U/l, P = 0.03). Also, segments showing reversible perfusion were significantly more frequent in group 2 (1/169 vs 57/481, P = 0. 01). During follow-up, no death occurred and the combined documented endpoint of reinfarction and recurrent angina requiring angioplasty or coronary artery bypass grafting was significantly more frequently reached in group 2 (0/13 vs 10/37, P = 0.046). In conclusion, RR is common (26%) after primary angioplasty for a first AMI and is associated with lesser myocardial damage on admission. Patients with RR rarely have reversible segments on 201Tl SPET and tend to have a favourable outcome after 1 year of follow-up.

Differentiation between recurrent brain tumour and post-radiation necrosis

The aim of this study was to determine whether it is possible to differentiate between recurrent disease and post-treatment necrosis in patients treated for a primary brain tumour. This prospective study was designed to compare the sensitivity and specificity of 201Tl single photon emission tomography (SPET) and 18F-fluorodeoxyglucose (18F-FDG) positron emission tomography (PET) using a dual-headed coincidence camera. Sixteen patients suspected of having recurrent brain tumour (10 men, 6 women) (mean age 39.5 years, range 21-57 years) were studied. 201Tl SPET and 18F-FDG PET studies were performed on the same day. An increase in activity was considered indicative of tumour recurrence. The images were also quantified using a thallium index and an FDG index. The 18F-FDG PET images were also assessed visually using a 5-point scale. The diagnosis of tumour recurrence was based on clinical course and/or follow-up computed tomography or magnetic resonance imaging. The sensitivity of 201Tl SPET and 18F-FDG PET was 92% (11/12) and 62% (7/12) respectively. One patient initially assessed as having necrosis showed a recurrence 9 months after both studies. McNemar's analysis of these results showed a statistically significant difference (P = 0.023) in the ability of the two methods to separate with accuracy tumour from radiation necrosis. No correlation was found between the thallium index and the FDG index (r = 0.36). We conclude that 201Tl SPET is a sensitive modality for the detection of brain tumour recurrence. 18F-FDG imaging using a dual-headed coincidence camera gave significantly poorer results compared to 201Tl SPET. Our results do not justify continuation of this prospective comparative study.

Prediction of post-revascularization functional recovery of asynergic myocardium using quantitative thallium-201 rest-redistribution tomography: has the reverse redistribution pattern an independent significance?

The significance of reverse redistribution on rest-redistribution thallium-201 myocardial scintigraphy is unclear. Previous studies suggested that reverse redistribution segments with normal resting activity include viable myocardium, whilst resting defects with further worsening correspond to scar. We evaluated whether reverse redistribution has an independent significance for the prediction of post-revascularization recovery, particularly as compared with the quantification of redistribution activity. We studied 26 coronary artery disease patients with left ventricular dysfunction, who underwent 201Tl rest-redistribution single-photon emission tomography (SPET) and echocardiography before revascularization. Viability was defined by the detection of wall motion improvement on follow-up echocardiography. 201Tl activity was considered normal if >/=80%, moderately reduced if <80% but >/=50%, and severely decreased if <50%. Reverse redistribution was defined as a defect in redistribution images with >/=10% decrease in relative 201Tl activity compared with the resting value. Reverse redistribution was detected in 33 segments (10%). Baseline dysfunction was equally observed in the reverse redistribution and in the non-reverse redistribution segments (64% vs 56%, P=0.40) and the rate of asynergic segments with post-revascularization recovery was not different between the two groups (33% vs 54%, P=0.11). The rate of functional recovery in redistribution defects without reverse redistribution was 53% in moderate and 30% in severe defects; the corresponding values for the reverse redistribution segments were 50% and 27% (all non-significant versus non-reverse redistribution segments). For the prediction of post-revascularization recovery in asynergic segments, the detection of reverse redistribution on rest-redistribution 201Tl SPET does not add any information to the quantitative analysis of redistribution activity.

Clinical value of triple-energy window scatter correction in simultaneous dual-isotope single-photon emission tomography with 123I-BMIPP and 201Tl.

To improve the image quality in simultaneous dual-isotope single-photon emission tomography (SPET) with iodine-123 labelled 15-(p-iodophenyl)-3-methylpentadecanoic acid (BMIPP) and thallium-201, we applied the triple-energy window method (TEW) for correction of the cross-talk and scatter artifact. Seventy-one patients with coronary artery disease were included. 201Tl cross-talk into the 123I acquisition window (group 1, n = 30) and 123I cross-talk into the 201Tl window (group 2, n = 41) were studied. In group 1, 123I images were first obtained (single-isotope images), followed by 201Tl injection and SPET acquisition using dual-isotope windows (dual-isotope images). In group 2, the order was reversed. The dual-isotope SPET images with and without TEW were compared with the single-isotope images. Qualitative evaluation was performed by scoring the segmental defect pattern. Detectability of the mismatched fatty acid metabolism on dual-isotope SPET was evaluated by receiver operating characteristic (ROC) curve analysis. Segmental defect pattern agreement between dual and corrected single images was significantly improved by TEW correction (P<0.01). The agreement was particularly improved in segments with absence of uptake. There was no significant difference between TEW-corrected dual-isotope SPET and corresponding single-isotope SPET with regard to either % defect count or background activity. Mismatched fatty acid metabolism depicted by dual-isotope SPET predicted abnormal wall motion more accurately with TEW than without TEW. With TEW, a practical method for scatter and cross-talk correction in clinical settings, simultaneous dual 123I-BMIPP/201Tl SPET is feasible for the assessment of myocardial perfusion/metabolism mismatch.

The diagnostic role of 201Tl SPET imaging in patients with lung tumours

The aim of the study was to evaluate the use of 201Tl single photon emission tomography (SPET) in differentiating histological types and lymph node sized of lung tumours based on the early uptake ratio (EUR), delayed uptake ratio (DUR) and retention index (RI). We also wished to compare the effectiveness of 201Tl SPET and computed tomography (CT) in detecting lymphadenopathy. We examined 41 subjects using both 201Tl SPET and CT. Fifty-seven lymph nodes were detected and were grouped according to size. The EUR, DUR and RI were determined and analysed using Student's t-test and a P-value < 0.05 was considered significant. Lymphadenopathy detected by both 201Tl SPET and CT correlated with the operative findings. There were no statistically differences in the EUR, DUR and RI between the various histological types. Statistically significant differences in EUR were noted between lymph nodes > 5 cm in size and those 3-5 cm in size, as well as between those < 3 cm and > 5 cm in size No significant differences were seen for the RI. The specificity, sensitivity and accuracy of 201Tl SPET were 81.3, 90.2 and 87.7% respectively, whereas for CT they were 81.3, 100 and 94.74% respectively. In conclusion, quantitative analysis with 201Tl SPET was unable to differentiate with accuracy between histological types but it could differentiate between nodes of varying sizes. However, CT had a better specificity and accuracy.

Relationship between thallium-201 uptake by supratentorial glioblastomas and their morphological characteristics on magnetic resonance imaging

Single-photon emission tomography (SPET) with thallium-201 is used in the assessment of patients with gliomas because the amount of 201Tl accumulated by the tumoral cells increases in proportion to the degree of tumour malignancy, thus making it possible to differentiate high-grade from low-grade gliomas or recurrences from radiation necrosis. However, in large areas of tissue such as those examined in 201Tl SPET studies, the uptake of 201Tl may vary considerably even in tumours with the same histological diagnosis, as occurs in glioblastomas (GBMs). In order to evaluate the possible influence of the macroscopic characteristics of tumours on 201Tl uptake, we studied a series of 13 patients with histologically proven GBMs, comparing magnetic resonance imaging (MRI) parameters such as tumour dimensions, perilesional oedema, intratumoral necrosis and contrast enhancement with the degree of 201Tl uptake. The patients underwent both 201Tl SPET and MRI before surgery. The 201Tl index (tumour/contralateral unaffected brain) was calculated using two different region of interest (ROI) methods: the first employed irregular large ROIs (3.2+/-13.9 cm2) including pixels with more than 50% maximum activity; the second employed regular square small ROIs (2.7 cm2) centered on the maximum activity of the lesion. Of the MRI morphological parameters studied, only necrosis significantly reduced the degree of 201Tl uptake in GBMs when larger ROIs were used. However, by using small regular ROIs the influence of necrosis on 201Tl uptake was found to be less relevant. Since necrosis is related to tumour proliferative activity and represents a negative prognostic factor in astrocytoma, a possible underestimation of 201Tl uptake due to intratumoral necrosis must be carefully evaluated.

The effect of steroid on thallium-201 uptake by malignant gliomas.

In order to assess the effect of steroid on thallium-201 uptake by glioma, 201Tl single-photon emission tomography was performed before and after steroid administration in four patients with recurrent malignant glioma. After steroid administration the 201Tl index, expressed as the ratio of 201Tl uptake in the tumour to that in the contralateral cerebral hemisphere, was 0.77+/-0.11 of the value before steroid (mean+/-SD: P<0.05 by paired t test). The 201Tl index has been used as a possible indicator for the differentiation of malignant gliomas from relatively benign tumours or radiation necrosis. The present results indicate that the effect of steroid has to be taken into account when semi-quantitative analysis, e.g. by means of the 201Tl index, is used in patients with brain tumours.

Identification of a hypoperfused segment in bull's-eye myocardial perfusion images using a feed forward neural network.

Artificial neural networks are computer systems which can be trained to recognize similarities in patterns and which learn by example; one of the more straightforward types being the feed forward neural network (FFNN). We previously reported the use of FFNNs for classification of hypoperfusion patterns in bull's-eye representation of 201Tl single photon emission tomography myocardial perfusion studies and showed that, when such an image was divided into 24 segments, FFNNs could detect perfusion defects without direct comparison to a normal data base. This has been extended in this investigation to assess the ability of an FFNN, trained on data in which only a single segment was hypoperfused, to detect this abnormal segment when the hypoperfusion pattern of the other segments in the image varied. The results indicated that the network could reliably determine whether a segment was normally or under perfused, with accuracies of 99% and 100%, respectively, if all other segments were normally perfused. It could also reliably detect a normally perfused segment, even if other segments were hypoperfused, with accuracies of 95% and 98%. The network was less reliable, however, in detecting a hypoperfused segment when other segments were also hypoperfused, showing accuracies of only 74% and 88%.

Thallium-201 myocardial SPET in strictly defined syndrome X

We reviewed the exercise thallium-201 (201Tl) myocardial single photon emission tomography (SPET) results and clinical data of 28 patients, adhering to a strict definition of syndrome X. All of the patients had a normal resting left ventricular ejection fraction (LVEF) and no cardiac abnormalities. The results of the exercise electrocardiography (ECG) studies were evaluated and compared with the results of 201Tl SPET. Of the 28 patients, only 3 (11%) had a normal 201Tl SPET scan and 25 (89%) had an abnormal 201Tl SPET scan. We found that a normal 201Tl SPET scan was rare when adhering to a strict definition of syndrome X, and the results of exercise ECG did not correlate well with the perfusion defects observed on the 201Tl SPET scan.

201T1 myocardial perfusion SPET: adenosine alone or combined with dynamic exercise

201Tl myocardial perfusion single photon emission tomography (SPET) with pharmacological coronary vasodilatation using adenosine is now often used in the investigation of a patient with ischaemic heart disease (IHD). In this study, we present data from two groups of patients. Group A (n = 40) experienced 201Tl SPET with adenosine only as the pharmacological stress test, using an infusion rate of 140 micrograms kg-1 min-1. Group B patients (n = 50) had the same test combined with low-level dynamic exercise. The side effects were noted for both groups and 201Tl SPET studies were acquired for stress and redistribution images. There was a lesser degree of non-cardiac side effects in patients of group B. There was a significant difference in the haemodynamic parameters between the two groups. There was no significant difference in overall sensitivity (87% versus 90%) and specificity (84% versus 88%) in the detection of IHD between the two groups. In conclusion, addition of low-level dynamic exercise with adenosine is to be preferred to adenosine infusion alone, as this protocol is better tolerated and may enhance the detection of right coronary artery disease (sensitivity = 82% versus 90%, n.s.).

Sensitivity and specificity of thallium-201 single-photon emission tomography in the functional detection and differential diagnosis of brain tumours.

The aim of this retrospective study was to assess the contribution of thallium-201 single-photon emission tomography (SPET) in the detection and differential diagnosis of brain tumours. In 90 patients 201Tl SPET was performed because of clinical or radiological suspicion of tumoral invasion, completed by technetium-99m hexamethylpropylene amine oxime and 99mTc-sestamibi SPET in some patients. For all tumours, diagnosis was based on biopsy or autopsy. Other diagnoses were made only after clinical and radiological follow-up for at least 6 months. Histologically tumours consisted of astrocytoma stage I or II (number of patients, n = 6), astrocytoma stage III (n = 8), glioblastoma multiforme (n = 14) and oligodendroglioma (n = 3), brain metastasis (n = 14), lymphoma (n = 3), meningioma (n = 3), pituitary adenoma (n = 2), pineal tumour (n = 1), colloid cyst (n = 1) and craniopharyngioma (n = 1). False-negative studies included pineal tumour (n = 1), colloid cyst (n = 1), craniopharyngioma (n = 1), astrocytomas stage I or II (n = 6) and stage III (n = 3), oligodendroglioma (n = 2) and metastasis in the brain stem (n = 1). Additional metastases approximately < 1.5 cm were not detected in two patients and 201Tl SPET underestimated tumoral extent in one patient suffering from glioblastoma multiforme (n = 1). A false-positive study was obtained in a patient with skull metastasis (n = 1). All 15 patients who were finally shown to suffer from ischaemic infarction had a normal SPET study 9-28 days after the onset of symptomatology. Of five patients with haemorrhagic infarction, studied within 2 weeks, four were false-positive. Of six patients with intracranial haemorrhage, studied 9-39 days later, one showed focal 201Tl accumulation. Two further false-positive studies consisted of angioma and epidural haematoma. Finally, SPET studies were normal in six patients with definite diagnosis of (reactive) gliosis (n = 3), Binswanger's encephalopathy (n = 1), postinfectious encephalopathy (n = 1) and multiple sclerosis (n = 1). In the patient population presented, sensitivity of 201Tl SPET for supratentorial brain tumours was 71.7% and specificity was 80.9%. Clinical information and control SPET studies in combination with early, 30-min and 3- to 4-h delayed imaging may be expected to improve on these figures. On the other hand it seems that, in addition to tumoral histology, the presence of tumours in the fossa posterior and small volumes contribute to the occurrence of false-negative 201Tl SPET studies.