The optimum time for tumour imaging with thallium-201

Following the intravenous injection of 75 MBq ²⁰¹Tl-chloride we have assessed the uptake kinetics in the myocardium and in the primary tumour in 56 patients with lung cancer, 26 with breast cancer and 13 with mediastinal lymphoma. The time of maximal tumour uptake ranged from 8–20 min post-injection and did not differ significantly between lung cancer (mean±SD=11.9±3.34 min), breast cancer (11.21±1.88 min) and lymphoma (11.76±3.25 min). The time of maximum cardiac uptake of ²⁰¹Tl was 11.61±3.25 min. There was no significant washout of ²⁰¹Tl from the tumours in the first hour after injection in the various malignant lesions studied. The time of maximal tumour to background activity was 18.3±0.59 min for lung cancer, 13.0±1.16 min for breast cancer and 16.7±1.04 min for lymphoma.The time course of ²⁰¹Tl uptake in the tumours suggests that the mechanism of uptake is similar to that in the myocardium. The optimal time of ²⁰¹Tl tumour imaging is from 20–60 min following injection and did not differ in various tumours studied.     

Cerebral blood flow imaging with thallium-201 diethyldithiocarbamate SPECT

Thallium-201 diethyldithiocarbamate ([201TI]DDC) was studied in humans as an agent for cerebral blood flow imaging. Brain uptake proved to be complete 90 sec after injection with no appreciable washout or redistribution for hours. Intracarotid injection suggested an almost 100% extraction during the first passage. Whole-body distribution studies demonstrated a brain uptake of 4.3% of the dose compared with 0.9% for [201TI]chloride. No differences were found in the distribution of [201TI]DDC versus [201TI]chloride in other organs. After the injection of 3 mCi 201TI, good quality single photon emission computed tomographic (SPECT) images of the brain were obtained with both a rotating gamma camera and a multidetector system. In ischemic brain disease, perfusion defects were easily demonstrated. We conclude that [201TI]DDC is a suitable radiopharmaceutical for SPECT studies of cerebral blood flow.     

Experience with thallium-201 imaging in head and neck cancer

TI-201 chloride was used for tumor imaging in patients with head and neck cancer. It is of value in detecting the extent of tumor involvement, the presence of residual tumor after radical courses of treatment, and the presence of local recurrence and distant metastases.     

Value of thallium-201 scintigraphy for primary tumour detection in patients with malignant neck masses

The aim of this study was to assess the contribution of thallium-201 scintigraphy to primary tumour detection in patients with malignant neck masses and to evaluate its sensitivity and specificity. A total of 30 patients with histopathologically proven malignant tumours were included in the study. The sensitivity, specificity and accuracy of ²⁰¹Tl scintigraphy were found to be 54%, 75% and 57% respectively. These results suggest that ²⁰¹Tl scintigraphy has a limited value in the detection of the primary tumour in patients with malignant masses of the neck. Received 14 November 1997 and in revised form 26 January 1998     

Study of ECG-gated thallium-201 myocardial scintigraphy: is imaging time a limiting factor?

Twenty patients underwent gated synchronized 201Tl myocardial scanning (TMS). Twelve also performed a rest blood pool multigated acquisition ( MUGA ) study. A 'static' image was obtained by adding all the gated frames of the study. In this way we found the conventional static study quite unnecessary. Comparing the gated TMS to the static one revealed significantly improved resolution in the gated images and additional information concerning wall motion and myocardial thickness. Close agreement was found with results of MUGA studies of the same patients. By the addition of diastolic frames the imaging time needed to obtain improved image quality was found to be not more than 10 min per view. The exclusion of imaging time as a limiting factor for gated TMS is stressed.     

Hyperventilation thallium-201 myocardial imaging for the diagnosis of vasospastic angina

In seven patients with vasospastic angina, a transient myocardial perfusion defect was demonstrated on Tl-201 myocardial imaging after hyperventilation (HV). The development of spasm on one or more coronary arteries after HV was confirmed by later coronary arteriographic studies, with the perfusing area of the coronary arteries being compatible with the scintigraphic location of the defect. Repeated 12-lead electrocardiograms failed to establish the diagnosis in one of the seven patients. It is concluded that HV Tl-201 myocardial imaging provides invaluable information in establishing a diagnosis of vasospastic angina.     

Comparison of techniques for thallium-201-technetium-99m parathyroid imaging

It is impracticable to compare the variety of techniques advocated for thallium-technetium (Tl-Tc) subtraction parathyroid imaging by repeated studies in patients. We therefore carried out studies using a phantom assembly to simulate thyroid and parathyroid in the neck, containing activities of 99Tcm and 201Tl similar to those likely to be present in patient imaging. An initial study of imaging protocol confirmed that correction for scatter from 99Tcm in the 201Tl window usefully improved the image. After making a preliminary selection of gamma cameras and collimators it was found that the GE Maxicamera 400T just visualized the 0.3 g "parathyroid" in a 5 min image with the pinhole collimator and 6 mm insert (A). It performed slightly less well with the HR converging collimator (B) and only marginally better with the 4 mm insert (C), but this is unduly slow unless it is placed close enough to limit the field of view unacceptably. The Siemens Orbiter 75 ZLC with special thyroid collimator (D) gave results similar to (A), is convenient for positioning the patient and is very suitable for parathyroid imaging.     

Rest-injected thallium-201 imaging for assessing viability of severe asynergic regions

To evaluate the utility of rest-injected 201Tl initial and delayed images for assessing the viability of severe asynergic regions, we studied 17 patients with apparently prior infarcted myocardium in combination with 99mTc ventriculography before and after revascularization. In 51 regions with severe asynergy, the percent 201Tl uptake was calculated as the ratio of counts on the segment with asynergy to the maximum counts on the normal segment. Eleven of 14 regions with resting 201Tl redistribution (Group 1) had improved wall motion after revascularization. However, 14 of 37 regions without redistribution also improved (Group 2). Twenty-three regions without redistribution or improved wall motion after revascularization (Group 3) had lower regional 201Tl uptake on their delayed images than those in Groups 1 and 2. Moreover, the initial regional uptake of Group 2 was higher than that of Group 3. These results suggest that redistribution on rest-injected 201Tl scans indicates reversibility of severely asynergic myocardium and that high 201Tl uptake in regions without redistribution may predict improvement in wall motion after revascularization. We conclude that 201Tl uptake may be useful as a marker of viability of severe asynergic regions before revascularization.     

Gliosarcoma with thallium-201 SPECT

Thallium-201 (201Tl) chloride scintigraphy is the imaging method use for the detection of various tumors including glioblastoma, but only limited information on 201Tl uptake in gliosarcoma is available. We investigated a patient with gliosarcoma by means of 201Tl single-photon emission computed tomography (SPECT) and MRI. SPECT imaging revealed high 201Tl uptake in the tumor, which was closely correlated with contrast-enhancement on MRI. These results suggest that SPECT with 201Tl may be useful for detecting gliosarcoma and provide physiological information on this tumor.     

False positive thallium-201 SPECT imaging in brain abscess

Three cases of intracranial 201Tl uptake, reported as positive tumour activity in patients with a final diagnosis of abscess, are described. 201Tl has been proposed as a useful oncotropic radiotracer in the diagnosis of brain tumour activity. These cases suggest a note of caution in the interpretation of 201Tl brain images in the differential diagnosis of an intracranial expanding mass.     

Quantative planar and tomographic thallium-201 myocardial perfusion imaging

Quantification of thallium myocardial studies affords the advantage of objectivity over visual analysis. Moreover, comparison of patient profiles to normal limits gives nonexpert readers a sense of confidence for interpreting these studies. Quantification of the washout rate from planar scintigrams aids in overcoming any lack of contrast. Tomography has excellent contrast resolution and identifies most stress perfusion defects without the need for washout calculations. Moreover, with the use of polar displays such as the Bullseye map, the perfusion defect is better characterized by tomography in terms of its location, shape, and size. The main caveat in the use of tomography is that it is technically demanding. The decision as to which method to use depends largely on the application and on the instrumentation and technical expertise available.     

Nuclear imaging of bone tumors: thallium-201 scintigraphy

(201)Tl scintigraphy provides important information for the management of patients with bone tumors. Although the role for staging the disease of bone tumors and for differentiation of benign from malignant lesions is limited, (201)Tl scintigraphy reflects the disease activity after treatment and it should be used to determine the treatment response and for early diagnosis of recurrence. Baseline study is essential for future reference to evaluate the response to preoperative chemotherapy and to detect recurrence after surgery. Sequential (201)Tl scintigraphy before and after treatment is useful in assessing the grade of response of the tumor to chemotherapy. The early prediction of chemotherapeutic effect by (201)Tl scintigraphy during treatment will affect the management of patients who do not respond to the therapy. This is of special importance to determine whether the patient needs an amputation or a limb-salvage surgery.     

Validation of a short-scan-time imaging protocol for thallium-201 myocardial SPECT with a multifocal collimator

Objective

IQ-SPECT (Siemens AG, Munich, Germany) is a highly sensitive single-photon-emission computed tomography (SPECT) myocardial perfusion imaging (MPI) system that uses a multifocal collimator. We searched for a suitable protocol for short-time imaging by IQ-SPECT in thallium-201 (Tl-201) MPI by evaluating phantom images and also by comparing human IQ-SPECT images with conventional SPECT images as reference standards.

Methods

We assessed the image quality using the normalized mean square error (NMSE) and drew up count profiles in Tl-201 SPECT images acquired with IQ-SPECT in a phantom study. We also performed Tl-201 stress myocardial SPECT/CT in 21 patients and compared delayed images acquired by using IQ-SPECT with 36 or 17 views per head with images obtained by using conventional SPECT.

Results

The NMSE of SPECT images from IQ-SPECT with 36 views was approximately one-fifth of that with 17 views. The myocardial count profile of images with 17 views was lower than those of images with 36 or 104 views in some regions. Defect scores were significantly lower, and image quality scores higher, in images from conventional SPECT than in those from IQ-SPECT with 17 views. Defect scores and image quality scores were equivalent in images from conventional SPECT and those from IQ-SPECT with 36 views. Agreement with the results of conventional SPECT in terms of coronary artery territory-based defect judgment was the best in IQ-SPECT with 36 views with computed tomography-derived attenuation correction (CTAC): the kappa values for IQ-SPECT with 36 views were 0.76 (without CTAC) and 0.83 (with CTAC), and those for IQ-SPECT with 17 views were 0.62 (without CTAC) and 0.59 (with CTAC). The difference in quantitative tracer uptake between conventional SPECT images and IQ-SPECT images was significantly greater for IQ-SPECT images with 17 views than for those with 36 views.

Conclusions

Scanning with 36 views per head with CTAC may be appropriate for Tl-201 MPI using IQ-SPECT, because it provides images equivalent to those using conventional SPECT.     

Relationship between thallium-201 uptake and tumour proliferative ability in thyroid nodules

To evaluate whether thallium-201 scan can reflect tumour proliferative activity in thyroid nodules. We compared the degree of 201T1 uptake with the tumour proliferative ability as assessed immunohistochmically by the labelling index of proliferating cell nuclear antigen (PCNA) in malignant and benign thyroid nodules. The case material comprised ten benign and 31 malignant surgically resected nodules from a total of 41 patients.²⁰¹TI scan was performed 5 min (early scan) and 2 h (delayed scan) after intravenous injection of 74 MBq of²⁰¹Tl. The degree of²⁰¹TI uptake was visually divided into three grades [from (-) to (++)], as compared with its uptake in normal adjacent thyroid tissue. Immunohistochemical staining of PCNA was performed using a monoclonal antibody for PC 10 on paraffin-embedded specimens. On both the early and the delayed scans, the mean PCNA index in the nodules with an intense²⁰¹T1, i.e. (++), was significantly higher than that in nodules with a lower or with negative 201T1 uptake. The correlation was higher on the delayed 201T1 scan (P=0.009) than on the early scan (P=0.019). Our results indicate that²⁰¹TI uptake may reflect the tumour proliferative activity of thyroid nodules, and this is especially true with regard to the uptake on delayed scans.     

Three-dimensional techniques and artificial intelligence in thallium-201 cardiac imaging

Three-dimensional reconstruction techniques including bull's-eye polar-coordinate maps, surface rendering, and surface modeling have been developed that help interpreting physicians assimilate complex 3-D tomographic data. Comparison of patient data with normal files highlights myocardial perfusion abnormalities, thus facilitating their recognition. In addition, AI systems that use heuristically defined rules derived from an expert knowledge base assist inexperienced observers in drawing conclusions regarding scan abnormalities.