201Tl as a tumour-localizing agent: current status and future considerations

To study the efficacy of thallium-201 as tumor seeking agent and to study its role in therapeutic response

BACKGROUND

Tumour seeking characteristics of TL-201 have been underutilized. The study was undertaken to evaluate the role of TL-201 scintigraphy in tumour imaging.

METHODS

A total of 50 cases were studied over a period of 18 months (13 lymphomas, 11 breast carcinoma, 10 lung cancer, 6 of soft tissue sarcoma, 2 bone tumours and 4 cases each of thyroid and brain tumours). Thallium-201 chloride was injected IV in the dose range of 3-5 mCi. Imaging was done using Siemen's ECAM dual headed gamma camera. Mean tumour to background ratio (T/B ratio) was calculated for all the positive cases. Descriptive statistical analysis was carried out.

RESULTS

Findings revealed a sensitivity of 94.12%, specificity 87.5%, PPV 94.12%, NPV 87.50% and accuracy of 92% for TL-201 tumour imaging. The mean T/B ratio for the true positive cases at 10 min and at 3 h was 1.81 and 1.99 respectively, the difference being 0.18 (P value <0.001). Amongst them, the mean T/B ratios for low-grade tumours were 1.45 ± 0.32 at 10 min and 1.63 ± 0.38 after 3 h with difference of 0.176 (P < 0.001). For the high-grade tumours the ratios were 2.08 ± 0.35 and 2.26 ± 0.41 respectively with a difference of 0.186 (P < 0.001).

CONCLUSION

Thallium-201 scintigraphy is a useful tumour imaging modality in cases of thyroid, breast, brain, lung, soft tissue and bone tumours and lymphomas. A T/B ratio of 1.63 ± 0.38 in 3 h-delayed imaging is suggestive of low-grade tumours. For high-grade tumours a ratio of 2.26 ± 0.41 should be considered significant.

[Value of thallium 201-SPECT in typing brain space-occupying lesions]

OBJECTIVE

This study was designed to assess the diagnostic accuracy of single photon emission computed tomography with Tl-201 (SPECT Tl-201) to establish the tumoral or non-tumoral nature of brain space occupying lesions in comparison with usual diagnostic techniques.

MATERIAL AND METHODS

The study population consisted of 37 patients, 24 men (64.9 %) and 13 women (35.1 %), mean age 48 +/- 16 years. After establishing the clinical and radiological diagnosis of brain lesion, all patients underwent SPECT Tl-201, evaluating it only by subjective analysis and blinded to neuroestructural techniques. After surgical resection all patients were evaluated anatomopathologically to establish the histologic nature.

RESULTS

The sensitivity of SPECT Tl-201 (0.87) was higher than standard neuroimaging techniques (0.78). Specificity (0.43), positive (0.87) and negative (0.43) predictive values of SPECT were similar to neuroestructural procedures (MRI and CT scan) with 0.43, 0.82 and 0.38 values. Tumoral disease prevalence was 0.81. Neuroestructural procedures were non-conclusive in 18.9 % of the studies. No non-conclusive results were obtained with SPECT Tl-201.

CONCLUSIONS

SPECT Tl-201 is a diagnostic procedure of high sensitivity to establish the tumoral nature of brain lesions, with poor specificity, similar to structural X-ray techniques.

Usefulness of thallium-201 SPECT scintimammography to differentiate benign from malignant breast masses in mammographically dense breasts

The purpose of this study was to assess the usefulness of thallium-201 (Tl-201) single-photon emission-computed tomography (SPECT) scintimammography to differentiate benign from malignant breast masses in 32 female Taiwanese patients with indeterminate mammographic probability of malignancy because of mammographically dense breasts. All breast masses were removed, and final histopathological diagnoses were obtained in all cases. The results showed that thallium-201 SPECT scintimammography findings were true-positive in 22 cases, false-positive in 1 case, true-negative in 7 cases, and false-negative in 2 cases. The diagnostic sensitivity, specificity, and accuracy were 91.7%, 87.5%, and 90.6%, respectively, for detecting breast cancer in mammographically dense breasts. In conclusion, thallium-201 SPECT scintimammography is a useful tool for differentiating benign from malignant breast masses in patients with indeterminate mammograms because of mammographically dense breasts.

Comparison of thallium-201 SPET and CT/MRI in the detection of residual/recurrent squamous cell carcinoma of the oral cavity

This study was designed to compare the effectiveness of thallium-201 single-photon emission tomography (SPET) and conventional imaging, comprising computed tomography (CT) and magnetic resonance imaging (MRI), in the detection of residual/recurrent squamous cell carcinoma (SCC) of the oral cavity. Thirty-two patients with clinically suspected recurrent SCC of the oral cavity were recruited. All patients underwent (201)Tl SPET and CT or MRI within 2 weeks. The final diagnoses were based on the histology of the biopsy specimen. (201)Tl SPET and CT/MRI both accurately detected 17 of 18 residual/recurrent tumours. CT/MRI yielded eight false-positive studies, whereas (201)Tl SPET successfully excluded all tumours. The sensitivity, specificity, positive and negative predictive values and accuracy of (201)Tl SPET for the detection of recurrent oral SCC were 94%, 100%, 100%, 93% and 97%, respectively. The sensitivity, specificity, positive and negative predictive values and accuracy of CT/MRI for the detection of recurrent oral SCC were 94%, 43%, 68%, 86% and 72%, respectively. Thallium-201 SPET is more accurate than conventional imaging (CT or MRI) in differentiating residual/recurrent oral SCC from post-therapy changes.

The role of thallium-201 whole body scan with pelvic SPECT in patients with uterine cervical cancer treated by radiation therapy: a preliminary report

Evaluation of tumor extent before treatment and its response to therapy is important. The aim of this report is to assess the usefulness with thallium-201 (Tl-201) imaging study including whole body scan and pelvic single photon emission computed tomography (SPECT) in patients with uterine cervical cancers treated by radiation therapy. Before irradiation, eleven patients received detailed physical examination and Tl-201 imaging studies. A 4-score grading system was set for evaluation. The interval between Tl-201 imaging follow-up and completion of radiotherapy is one to four months, and its findings were compared with those from CT scan and clinical evidence. Before radiation, left supraclavicular and paraaortic lymphadenopathy was identified in one patient from whole body scan. Accumulation of Tl-201 uptake is observed from pelvic SPECT in all patients. It seems that patients with more tumor bulk had more intense uptake, except for one case with history of suspected pelvic inflammatory disease (PID). After radiotherapy, complete or partial regression is observed. For 6 patients with complete regression (score = 0), no evidence of recurrence is confirmed by follow-up examinations. For three patients with little residual uptake (score = 1), one is suspected with residual density and she is under close follow-up, the other two patients seem due to uterine myoma or short latency. These three patients received another Tl-201 scan 6 months after irradiation completion and the score became zero. One patient with residual intense uptake (score = 2) suffered from relapse in the pelvis and abdomen. This preliminary report indicates that Tl-201 whole body scan and pelvic SPECT has potential in the assessment of response to radiotherapy in patients with uterine cervical cancers. However, further studies including more cases and longer follow-up are needed.

Using thallium-201 SPECT to detect recurrent or residual nasopharyngeal carcinoma after radiotherapy in patients with indeterminate CT findings

BACKGROUND

The aim of this study is to evaluate the usefulness of thallium-201 (Tl-201) single-photon emission CT (SPECT) to detect recurrent or residual nasopharyngeal carcinomas (NPC) when CT findings are indeterminate.

METHODS

After radiotherapy, 30 NPC patients with indeterminate CT findings were included. CT, Tl-201, and biopsy were performed at least 4 months after radiotherapy and within 1 week of each other. The final results were based on histopathologic findings and clinical follow-up after at least 6 months.

RESULTS

The rates for sensitivity, specificity, and accuracy of Tl-201 SPECT in detecting recurrent or residual NPC when there were indeterminate CT findings, were 86.7%, 93.3%, and 90.0%, respectively.

CONCLUSIONS

These results suggest that Tl-201 SPECT is effective in detecting recurrent or residual NPC when CT findings are indeterminate.

Differentiation of soft tissue haemangioma by 201Tl scintigraphy

Radiological diagnosis of deep soft tissue is often difficult. In the present study, thallium-201 ( Tl) uptake into haemangiomas and deep malignant soft tissue tumours was investigated in order to assess its clinical utility. Tl scintigraphy was reviewed in four patients presenting with soft tissue haemangiomas. Early and delayed planar images, obtained at 15 min and 3 h following the intravenous injection of Tl (111 MBq), were examined. The Tl uptake ratio was calculated by dividing the count density of the tumour region of interest (ROI) by that of the background ROI. Results were compared with those of five cases of rhabdomyosarcoma and a single instance of angiosarcoma. All haemangioma lesions demonstrated increased Tl uptake in early images. However, Tl uptake in delayed images was markedly decreased. No significant differences were observed in the early uptake ratio between haemangiomas (1.60-2.72) and reference malignant tumours (1.48-2.45); however, the difference was significant in delayed images (range, 1.01-1.26 vs. 1.43-2.03, respectively) ( P<0.02). Deep soft tissue haemangiomas revealed Tl accumulation in early images; however, a rapid washout was observed in delayed images. This distinctive feature may facilitate the use of Tl scintigraphy in the diagnosis of haemangiomas.

Detection of recurrent nasopharyngeal carcinomas with thallium-201 single-photon emission computed tomography in patients with indeterminate magnetic resonance imaging findings after radiotherapy

BACKGROUND

The aim of this study was to evaluate the usefulness of thallium-201 (Tl-201) single-photon emission CT (SPECT) to detect recurrent nasopharyngeal carcinomas (NPC) when MRI findings are indeterminate.

METHODS

After radiotherapy, 26 NPC patients with indeterminate MRI findings were included in this study. MRI, Tl-201, and biopsy were performed at least 4 months after radiotherapy and within 1 week. The final results were based on histopathologic findings and clinical follow-up after at least 6 months.

RESULTS

For detecting recurrent NPC in indeterminate MRI findings, the sensitivity, specificity, and accuracy of Tl-201 SPECT were 92.3%, 92.3%, and 92.3%, respectively.

CONCLUSIONS

On the basis of this result, Tl-201 SPECT seems to be effective in detecting recurrent NPC when MRI findings are indeterminate.

Comparison of the uptake and clearance of Tc-99m MIBI, Tl-201 and Ga-67 in drug-resistant lymphoma cell lines

Tc-99m sestamibi (MIBI) has been used as a tumor-seeking agent. However, its role in detecting lymphomas has not been widely investigated. The aim of the present study was to determine the uptake and clearance characteristics of Tc-99m MIBI in vincristine-resistant lymphoma cell lines. In addition, thallium-201 (Tl-201) and gallium-67 (Ga-67) uptake and clearance characteristics were evaluated for comparison with Tc-99m MIBI. Drug-resistant lymphoma cell lines (monocyte-like, histiocytic lymphoma, human; B-lymphoma cell line, American Burkitt lymphoma, lymphoblastoid, human; Hodgkin's disease, lymphoid, human) were selected by multistep vincristine treatment up to 50 nM. After incubation of the radiotracers, Tc-99m MIBI, Tl-201 and Ga-67, in medium for 0, 10, 20, 30, 60 or 120 min, the uptake and clearance of each radiotracer were measured in the drug-resistant lymphoma cell lines. In addition, P-glycoprotein expression was determined by immunohistochemical study. In a comparison of the three radiotracers, the uptake of Tc-99m MIBI was the greatest in the studied wild-type lymphoma cell lines. Tc-99m MIBI uptake was much lower in drug-resistant tumor cell lines than in non-resistant cell lines. On the other hand, the uptake characteristics of Tl-201 did not differ between drug-resistant and non-resistant cells. Immunohistochemistry analyses of Ab-1 or JSB indicated that tumor cells expressed MDR-1 protein in all three cell lines. Tc-99m MIBI is a good radiotracer for detecting drug resistance in lymphoma cell lines.

Thymic lesions in patients with myasthenia gravis: characterization with thallium 201 scintigraphy

PURPOSE

To assess thallium 201 ((201)Tl) single photon emission computed tomography (SPECT) for evaluation of thymic lesions associated with myasthenia gravis (MG), including lymphoid follicular hyperplasia (LFH) and thymoma.

MATERIALS AND METHODS

(201)Tl SPECT and computed tomography (CT) were performed preoperatively in 46 patients with MG who had undergone thymectomy. SPECT was conducted 15 (early image) and 180 (delayed image) minutes after (201)Tl injection. Results were visually assessed, and (201)Tl uptake ratios (thymic lesion count density/lung count density) were measured for quantitative analysis. Uptake was analyzed among the normal thymus, LFH, and thymoma patient groups.

RESULTS

Histopathologic results indicated a normal thymus, LFH, and thymoma in 19, 16, and 11 patients, respectively. Mean uptake ratios in the normal thymus, LFH, and thymoma were 0.96 (95% CI: 0.90, 1.03), 1.14 (95% CI: 1.04, 1.25), and 1.87 (95% CI: 1.56, 2.25), respectively, on early images and 1.09 (95% CI: 1.00, 1.18), 1.65 (95% CI: 1.48, 1.85), and 2.03 (95% CI: 1.65, 2.50), respectively, on delayed images. Thymoma showed more intense (201)Tl accumulation than did the normal thymus (P <.001) and LFH (P <.001) on early images. Both thymoma (P <.001) and LFH (P <.001) displayed more intense uptake than did the normal thymus on delayed images.

CONCLUSION

(201)Tl SPECT can enable differentiation between normal thymus, LFH, and thymoma in patients with MG.

Evaluation of 201T1 SPECT for predicting early treatment response in patients with squamous cell carcinoma of the extracranial head and neck treated with nonsurgical organ preservation therapy: initial results

PURPOSE

The purpose of this work was to prospectively determine the ability of 210TI single photon emission CT (SPECT) to monitor treatment response in patients with head and neck squamous cell carcinoma (HNSCCA) treated with nonsurgical organ preservation.

METHOD

Nine patients with HNSCCA underwent 201T1 SPECT before and 6 weeks after completion of nonsurgical organ preservation therapy. All cases were evaluated for uptake at the primary site before and after treatment. All tumors had abnormal radiotracer uptake on the pretreatment study. The posttreatment thallium studies were evaluated for uptake and correlated with local control at the primary site in all cases.

RESULTS

All patients had abnormal thallium uptake on pretreatment studies. Of the nine patients, four cases were locally controlled by nonsurgical organ preservation therapy. All of these patients had no evidence of thallium uptake on posttreatment studies. Five cases failed treatment at the primary site. All five patients demonstrated abnormal radiotracer uptake at the primary site.

CONCLUSION

Our initial results suggest that 201T1 SPECT may be an accurate technique for monitoring HNSCCA treated with nonsurgical organ preservation therapy.

Osteoradionecrosis of the hyoid bone: a report of 3 cases

PURPOSE

Osteonecrosis of the hyoid bone is an uncommon disease that has only been described occasionally in the literature.

MATERIALS AND METHODS

We report 3 cases of osteonecrosis of the hyoid bone after radiation therapy for carcinoma at various sites in the head and neck region.

RESULTS

Imaging computed tomography (CT) scans were performed for all 3 cases and did aid in the diagnosis. In 1 case, a 201thallium scintigraphy and a bone scan (99mtechnetium-diphosphonate) were performed and this confirmed the diagnosis of osteoradionecrosis.

CONCLUSION

Osteoradionecrosis of the hyoid bone may be misdiagnosed as recurrent neoplasm. Although recurrent or persistent neoplastic disease must initially be ruled out, it is subsequently important to correctly identify osteonecrosis of the hyoid bone, because its surgical treatment is simple and the prognosis is good.

Uptake of cationic technetium complexes in cultured human carcinoma cells and human xenografts

We evaluated lipophilicity, in vitro cell accumulation, and biodistribution of a series of 99mTc-ether isonitrile complexes to determine whether increased lipophilicity promotes extraction by tumor or enhances imaging properties of the radiopharmaceutical. Nine 99mTc-sestamibi analogs were synthesized and their lipophilicity was determined. Net cellular accumulation and membrane-potential-independent uptake were quantitatively compared in cultured human colon, breast, and lung carcinoma cells. The biodistribution of [99mTc-(2-methoxy-2-ethyl-isocyanopropane)6]+ (99mTc-MMBI) and [99mTc-(2-ethoxy-2-methyl-1-isocyanopropane)6]+ (99mTc-EIBI) was studied in nude mice using subcutaneous, subrenal capsule, and hepatic tumor xenografts. Accumulation of these compounds in colon cells correlated with increasing lipophilicity. Compared with 99mTc-sestamibi, 99mTc-EIBI exhibited (i) in colon cells both higher net accumulation and a higher specific/nonspecific uptake ratio; (ii) in all three cell lines higher membrane-potential-dependent accumulation; and (iii) in all subcutaneous tumor xenografts and in colon subrenal capsule and hepatic tumor xenografts higher tumor/background ratios.

Perfusion and thallium single photon emission computed tomography in herpes simplex encephalitis

This is the first report on 201thallium-single photon emission computed tomography (201Tl-SPECT) brain scan of a patient with herpes simplex encephalitis (HSE). The presented 201Tl-SPECT observations are correlated with 99mtechnetium hexamethylpropylene amine oxime (99mTc-HMPAO) perfusion SPECT and magnetic resonance imaging (MRI) findings. Brain 99mTc-HMPAO perfusion SPECT reveals a hyperperfusion in the right temporal lobe with extension to the parietal lobe and a hypoperfusion in the ipsilateral occipital lobe. 201Tl-SPECT shows a fixation in the right temporal lobe coinciding with the gadolinium enhancement on MRI. The right occipital lesion shown by gadolinium captation on MRI and hypoperfusion on 99mTc-HMPAO perfusion SPECT was not evident on the 201Tl SPECT. These findings could illustrate that the lesions might be different pathophysiologically.

Tl-201 scintigraphy, mammography and ultrasonography in the evaluation of palpable and nonpalpable breast lesions: a correlative study

PURPOSE

To determine the feasibility of Tl-201 as a tumor localizing agent in palpable and nonpalpable breast lesions, in comparison with mammography and ultrasonography (US), and to evaluate the contribution of these modalities to each other in obviating biopsy.

MATERIALS AND METHODS

Seventy-two palpable and nonpalpable breast lesions were prospectively classified as benign, indeterminate, or malignant according to the sonographic and mammographic criteria and were further analyzed with Tl-201 scanning. These classifications were compared with biopsy results. The sensitivity, specificity, accuracy, false positive and false negative rates (FPR, FNR), negative and positive predictive values (npv, ppv) were calculated for each individual modality and combination of modalities to evaluate the contribution of these three techniques to each other.

RESULTS

Of 72 lesions 52 were histologically malignant and 20 were benign. Overall, mammography was the most sensitive (92%) and Tl-201 was the most specific (75%) of the three modalities. Mammography + Tl combination was the most specific (90%) and accurate (97%) of dual combinations. In mammographically or sonographically indeterminate cases, Tl-201 was much more specific (75% versus 37% for mammography and US) and more accurate (82% versus 36% for mammography and 54% for US) than the other two modalities, and mammography + Tl combination was significantly superior to other dual combinations (87% specific and 91% accurate). Use of Tl-201 scanning as an adjunct to mammography + US combination increased the specificity, ppv, and accuracy rates overall, particularly in mammographically or sonographically indeterminate cases.

CONCLUSIONS

In mammographically and sonographically indeterminate breast lesions thallium scanning may be offered as a third step of investigation to obviate biopsy.

Tl-201 uptake and retention in a Warthin's tumor

We report scan findings of Tl-201 in a case of histologically proved Warthin's tumor. Dual isotopes acquisition was performed in a case of left parotid Warthin's tumor. Both early and delayed Tc-99m-pertechnetate (Tc-99m) images showed increased uptake at the tumor. Tl-201 scan also showed an increase of uptake on the early image and retention on the delayed image. The uptake ratios of Tl-201 were 3.0 (early) and 2.3 (delayed). Scan findings of Tl-201 in a case of Warthin's tumor were similar to those of Tc-99m, and the interpretation of Tl-201 images should be accompanied with Tc-99m images.

Evaluation of palpable breast masses with 201Tl scintigraphy

39 female patients (age range: 31-84 years) with palpable breast masses detected by physical examination, underwent 201Tl scintigraphy in order to assess its value in the detection of breast carcinomas and to differentiate them from benign breast masses. Planar images were carried out at 20-30 min and 2-3 h after intravenous administration of 111-185 MBq (3-5 mCi) of 201Tl chloride. In 12 patients single photon emission tomography (SPET) studies were also performed. In 18 patients the scintigraphic studies were positive and in 17 of these cases, breast carcinomas were confirmed. Tumour sizes ranged from 1.3 to 6 cm in diameter. In the remaining patient a false positive result was obtained where there was benign breast change. In three of seven cases, malignant axillary nodes were also detected. All 21 patients with negative scintigraphy had benign breast lesions. There were no differences between images obtained at 20-30 min and 2-3 h or between planar images and SPET studies. In 10 patients there was disagreement between mammography and 201Tl scans. 201Tl scans confirmed the presence of carcinoma in three cases and discarded malignancy in the other six cases. In the remaining case, 201Tl scan was false positive. 201Tl scintigraphy is useful in distinguishing malignant from benign breast masses, even when compared with mammography.

The use of thallium-201 in the preoperative detection of breast cancer: an adjunct to mammography and ultrasonography

Thallium-201 breast scans were performed preoperatively in 72 female patients with breast abnormalities detected by mammography and/or ultrasonography (7.5-13 MHz), in order to differentiate benign from malignant breast disease. Informed consent was obtained from each patient. Scintigraphy consisted of anterior and oblique planar images of the affected breast and axilla at 10 min and 3 h following the injection of 201Tl chloride (110 MBq). All 201Tl scans were interpreted without prior knowledge of surgery data. Pathological features of breast malignancies, such as tumour size, axillary lymph node metastases, tumour grading, lymphatic vascular channel invasion and receptor status, were analysed for their association with 201Tl uptake by tumour cells. A total of 76 breast lesions were assessed in the study. On final histological diagnosis, there were 56 malignant tumours, 14 benign nodules (9 fibroadenomas, two cases of adenosis, two cases of focal fibrosis and one case of epitheliosis) and six atypical lesions (atypical ductal or lobular hyperplasia). Thallium scintigraphy was shown to have high accuracy (92%) in detecting breast cancer, better than mammography (74%) and ultrasonography (84%). Almost all (51/56) breast cancers showed greater 201Tl activity than surrounding normal breast tissue while there was no significant increase in 201Tl activity above background in all but one (19/20) case of non-malignant disease. 201Tl activity within breast tumours, calculated as tumour/background (T/B) ratio, ranged between 1.2 and 2.5 with a mean value of 1.45. In our experience the concentration of thallium in the breast cancer seems to be primarily dependent on vascularity and tumour size rather than tumour grading, lymphatic/vascular invasion or receptor status. 201Tl scan sensitivity was 97% for malignant lesions larger than 1.5 cm (n = 35) and 80% for lesions of 1.5 cm or less (n = 21); however, five of the eight breast cancers smaller than 1.0 cm were also detectable by 201Tl scintigraphy, compared with five out of seven by mammography. Thallium scintigraphy would not be useful in evaluating the axilla for lymph node metastases (sensitivity 27%, specificity 77%).

Incidental detection of breast cancer during T1-201 myocardial SPECT study

A case of left breast cancer which was detected incidentally by T1-201 SPECT performed to evaluate the status of myocardial perfusion, is reported. Both stress and redistribution T1-201 SPECT clearly delineated the tumor. It was confirmed later as scirrhous carcinoma of the breast.

Technetium-99m-tetrofosmin uptake in malignant lung tumours

Technetium-99m-tetrofosmin is a new myocardial imaging agent which has yielded promising results compared to thallium-201. The tumour-seeking properties of the routinely used cardiac radiopharmaceuticals 201TI and 99mTc-methoxyisobutylisonitrile are well known. Here we report the results of a pilot study demonstrating 99mTc-tetrofosmin uptake in malignant lung tumours. Five patients with bronchial carcinoma, each in different stages of chemo- or radiotherapy, were imaged. Dynamic and static acquisitions were performed to evaluate the uptake and kinetics of 99mTc-tetrofosmin in the lesions. In four of the five patients localized tumour uptake of 99mTc-tetrofosmin was observed. Time to peak tumour activity and tracer washout in the tumour, myocardium and contralateral normal lung at 30 min post injection (p.i.) were determined. Tumour/normal lung, heart/tumour and heart/contralateral normal lung ratios were calculated for 5-10, 25-30 and 85-90 min p.i. The peak concentration in all tumours was reached at the end of the first minute. The mean tumour and contralateral normal lung washout rates of 99mTc-tetrofosmin at 30 min p.i. were 18.3% +/- 9.2% and 19.5% +/- 5.85% respectively. The tumour/contralateral normal lung ratio remained higher than 1.25 until 90 min p.i. in all four patients. It is concluded that 99mTc-tetrofosmin seems to be of value in lung tumour imaging, although larger studies are necessary to ascertain its sensitivity, specificity and usefulness in clinical practice.

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.

Avid thallium-201 uptake in hepatic carcinoid metastases

While radiolabelled somatostatin analogues sensitively detect extrahepatic carcinoid tumour, intrahepatic metastases are frequently not visualised due to somatostatin accumulation in normal hepatic tissues. We report a case of avid thallium-201 uptake in multiple hepatic carcinoid metastases using single-photon emission tomography (SPET) and compare this to a SPET technetium-99m sulphur colloid scan in the same patient. The 99mTc sulphur colloid images demonstrate multiple focal defects at the site of known metastases in the hepatic right lobe (confirmed on both CT and surgery). However, there is avid uptake of thallium in the metastases on comparative SPET slices. 201Tl may be a useful agent for the detection and localisation of carcinoid tumour and in particular of intrahepatic carcinoid metastases.