Brain tumor imaging with 99mTc-tetrofosmin: comparison with 201Tl, 99mTc-MIBI, and 18F-fluorodeoxyglucose

Brain SPECT and perfusion MRI: do they provide complementary information about the tumour lesion and its grading?

AIM

To evaluate the relative and combined utility of ^99mTc-tetrofosmin (^99mTc-TF) brain single-photon-emission computed tomography (SPECT) and dynamic susceptibility contrast (DSC) perfusion magnetic resonance imaging (MRI) in grading brain gliomas.

MATERIALS AND METHODS

Thirty-six patients with clinically suspected brain tumours were assessed by ^99mTc-TF SPECT and DSC-MRI. Brain tumour malignancy was confirmed in all patients at histopathology. On both techniques brain lesions were evaluated via visual and semi-quantitative analysis methods (deriving tetrofosmin index [T-index] and relative cerebral blood volume [rCBV] ratios, respectively).

RESULTS

^99mTc-TF SPECT showed abnormally elevated tracer uptake in 31/36 patients whereas MRI detected the brain tumour in all patients. Optimal cut-off values of each index for discriminating between low- and high-grade gliomas were obtained through receiver operating characteristic (ROC) analyses. A T-index cut-off of 6.35 ensured 82% sensitivity and 71% specificity for discriminating between high- and low-grade gliomas, whereas a relative rCBV ratio cut-off of 1.80 achieved 91% sensitivity and 100% specificity. Requiring a positive result on either technique to characterise a high-grade glioma was associated with similar specificity and slightly increased sensitivity.

CONCLUSION

Both imaging techniques, ^99mTF SPECT and DSC MRI, may provide complementary indices of tumour grade and have an independent diagnostic value for high-risk tumours.

Synthesis and evaluation of 99mTc/Re-tricarbonyl complexes of the triphenylphosphonium cation for mitochondrial targeting

INTRODUCTION

Lipophilic delocalized cations accumulate in tumor cell mitochondria due to their higher transmembrane potential. In this work, this strategy was adopted for the development of ^99mTc tumor-targeted imaging agents.

METHODS

Two tridentate ligands containing the triphenylphosphonium cation, L1 (S-cysteinyl) and L2 (N-iminodiacetate) as well as the respective ^99mTc/ReL1 and ^99mTc/ReL2 tricarbonyl complexes were synthesized. The effect of the ligands and the Re complexes on cell growth in U-87 MG glioblastoma cells was assessed. In vitro stability studies and measurement of logP of the ^99mTc tracers was performed. The cellular and mitochondrial uptake of the ^99mTc tracers in U-87 MG cells was evaluated. Biodistribution of ^99mTcL1 and ^99mTcL2 were performed on SCID mice bearing U-87 MG tumors.

RESULTS

The ligands L1, L2 and the Re1 and ReL2 complexes were characterized spectroscopically. Single products ^99mTcL1 and ^99mTcL2, >90% stable in rat serum, were obtained. LogP was 0.40±0.14 for ^99mTcL1 and -0.02±0.07 for ^99mTcL2. L1, ReL1 and ReL2 caused no notable cytotoxicity and L2 was found to infer 40% inhibition of cellular growth at 10^-5M as well as 80% cell death in culture at 10^-4M. The cell uptake of ^99mTcL1 and ^99mTcL2 over 4h was 1.26±0.08% and 0.06±0.01% respectively, of which 13.41±3.63% and 18.61±6.19% was distributed in the mitochondria respectively. The initial tumor uptake in mice was found to be >1% ID/g for both ^99mTc tracers.

CONCLUSIONS

In vitro mitochondrial and in vivo tumor targeting was observed, better in ^99mTcL1, however these properties should be optimized in future studies. Advances in Knowledge and Implications for Patient Care: Continuous efforts in this direction may lead to a suitable mitochondrial-targeted ^99mTc imaging agent for tumor detection.

Comparison of (99m)tc-tetrofosmin and (99m)tc-sestamibi uptake in glioma cell lines: the role of p-glycoprotein expression

^99mTc-Tetrofosmin (^99mTc-TF) and ^99mTc-Sestamibi (^99mTc-MIBI) are SPECT tracers that have been used for brain tumor imaging. Tumor's multidrug resistance phenotype, namely, P-glycoprotein (p-gp), and the multidrug resistance related proteins (MRPs) expression have been suggested to influence both tracers' uptake. In the present study we set out to compare ^99mTc-TF and ^99mTc-MIBI uptake in high-grade glioma cell lines and to investigate the influence of gliomas p-gp expression on both tracers' uptake. We used four glioma cell lines (U251MG, A172, U87MG, and T98G). The expression of p-gp protein was evaluated by flow cytometry. Twenty μCi (7.4·10⁵ Bq) of ^99mTc-TF and ^99mTc-MIBI were used. The radioactivity in the cellular lysate was measured with a dose calibrator. P-gp was significantly expressed only in the U251MG cell line (P < 0.001). In all gliomas cell lines (U251MG, U87MG, A172, and T98G) the ^99mTc-TF uptake was significantly higher than ^99mTc-sestamibi. The U251MG cell line, in which significant p-gp expression was documented, exhibited the strongest uptake difference. ^99mTc-TF uptake was higher than ^99mTc-MIBI in all studied high-grade glioma cell lines. Thus, ^99mTc-TF may be superior to ^99mTc-MIBI for glioma imaging in vivo.

Progress on the diagnosis and evaluation of brain tumors

Brain tumors are one of the most challenging disorders encountered, and early and accurate diagnosis is essential for the management and treatment of these tumors. In this article, diagnostic modalities including single-photon emission computed tomography, positron emission tomography, magnetic resonance imaging, and optical imaging are reviewed. We mainly focus on the newly emerging, specific imaging probes, and their potential use in animal models and clinical settings.

Biological characterization of F-18-labeled rhodamine B, a potential positron emission tomography perfusion tracer

INTRODUCTION

Myocardial infarction is the leading cause of death in western countries, and positron emission tomography (PET) plays an increasing role in the diagnosis and treatment planning for this disease. However, the absence of an (18)F-labeled PET myocardial perfusion tracer hampers the widespread use of PET in myocardial perfusion imaging (MPI). We recently reported a potential MPI agent based on (18)F-labeled rhodamine B. The goal of this study was to more completely define the biological properties of (18)F-labeled rhodamine B with respect to uptake and localization in an animal model of myocardial infarction and to evaluate the uptake (18)F-labeled rhodamine B by cardiomyocytes.

METHODS

A total of 12 female Sprague Dawley rats with a permanent ligation of the left anterior descending artery (LAD) were studied with small-animal PET. The animals were injected with 100-150 μCi of (18)F-labeled rhodamine B diethylene glycol ester ([(18)F]RhoBDEGF) and imaged two days before ligation. The animals were imaged again two to ten days post-ligation. After the post-surgery scans, the animals were euthanized and the hearts were sectioned into 1mm slices and myocardial infarct size was determined by phosphorimaging and 2,3,5-triphenyltetrazolium chloride staining (TTC). In addition, the uptake of [(18)F]RhoBDEGF in isolated rat neonatal cardiomyocytes was determined by fluorescence microscopy.

RESULTS

Small-animal PET showed intense and uniform uptake of [(18)F]RhoBDEGF throughout the myocardium in healthy rats. After LAD ligation, well defined perfusion defects were observed in the PET images. The defect size was highly correlated with the infarct size as determined ex vivo by phosphorimaging and TTC staining. In vitro, [(18)F]RhoBDEGF was rapidly internalized into rat cardiomyocytes with ~40 % of the initial activity internalized within the 60 min incubation time. Fluorescence microscopy clearly demonstrated localization of [(18)F]RhoBDEGF in the mitochondria of rat cardiomyocytes.

CONCLUSION

Fluorine-18-labeled rhodamine B diethylene glycol ester ([(18)F]RhoBDEGF) provides excellent image quality and clear delineation of myocardial infarcts in a rat infarct model. In vitro studies demonstrate localization of the tracer in the mitochondria of cardiac myocytes. In combination, these results support the continued evaluation of this tracer for the PET assessment of myocardial perfusion.

Target localization using scanner-acquired SPECT data

Target localization using single photon emission computed tomography (SPECT) and planar imaging is being investigated for guiding radiation therapy delivery. Previous studies on SPECT-based localization have used computer-simulated or hybrid images with simulated tumors embedded in disease-free patient images where the tumor position is known and localization can be calculated directly. In the current study, localization was studied using scanner-acquired images. Five fillable spheres were placed in a whole body phantom. Sphere-to-background 99mTc radioactivity was 6:1. Ten independent SPECT scans were acquired with a Trionix Triad scanner using three detector trajectories: left lateral 180°, 360°, and right lateral 180°. Scan time was equivalent to 4.5 min. Images were reconstructed with and without attenuation correction. True target locations were estimated from 12 hr SPECT and CT images. From the 12 hr SPECT scan, 45 sets of orthogonal planar images were used to assess target localization; total acquisition time per set was equivalent to 4.5min. A numerical observer localized the center of the targets in the 4.5 min SPECT and planar images. SPECT-based localization errors were compared for the different detector trajectories. Across the four peripheral spheres, and using optimal iteration numbers and postreconstruction smoothing, means and standard deviations in localization errors were 0.90 ± 0.25 mm for proximal 180° trajectories, 1.31 ± 0.51 mm for 360° orbits, and 3.93 ± 1.48 mm for distal 180° trajectories. This rank order in localization performance is predicted by target attenuation and distance from the target to the collimator. For the targets with mean localization errors &lt; 2 mm, attenuation correction reduced localization errors by 0.15 mm on average. The improvement from attenuation correction was 1.0 mm on average for the more poorly localized targets. Attenuation correction typically reduced localization errors, but for well-localized targets, the detector trajectory generally had a larger effect. Localization performance was found to be robust to iteration number and smoothing. Localization was generally worse using planar images as compared with proximal 180° and 360° SPECT scans. Using a proximal detector trajectory and attenuation correction, localization errors were within 2 mm for the three superficial targets, thus supporting the current role in biopsy and surgery, and demonstrating the potential for SPECT imaging inside radiation therapy treatment rooms.

SPECT and PET imaging of meningiomas

Meningiomas arise from the meningothelial cells of the arachnoid membranes. They are the most common primary intracranial neoplasms and represent about 20% of all intracranial tumors. They are usually diagnosed after the third decade of life and they are more frequent in women than in men. According to the World Health Organization (WHO) criteria, meningiomas can be classified into grade I meningiomas, which are benign, grade II (atypical) and grade III (anaplastic) meningiomas, which have a much more aggressive clinical behaviour. Computed Tomography (CT) and Magnetic Resonance Imaging (MRI) are routinely used in the diagnostic workup of patients with meningiomas. Molecular Nuclear Medicine Imaging with Single Photon Emission Computed Tomography (SPECT) and Positron Emission Tomography (PET) could provide complementary information to CT and MRI. Various SPECT and PET tracers may provide information about cellular processes and biological characteristics of meningiomas. Therefore, SPECT and PET imaging could be used for the preoperative noninvasive diagnosis and differential diagnosis of meningiomas, prediction of tumor grade and tumor recurrence, response to treatment, target volume delineation for radiation therapy planning, and distinction between residual or recurrent tumour from scar tissue.

Relation between (99m)Tc-tetrofosmin thyroid scintigraphy and mitogen-activated protein kinase in papillary thyroid cancer patients

PURPOSE

The aim of this study was to investigate the relation between (99m)Tc-tetrofosmin uptake and extracellular signal-regulated kinase mitogen-activated protein kinase (ERK MAPK) expression in papillary thyroid cancer patients.

MATERIALS AND METHODS

Our study population consisted of 14 patients. The histopathological findings for all patients were confirmed by surgery. Patients were administ 740 MBq of (99m)Tc-tetrofosmin. The tumor/background (T/B) ratios in regions of interest (ROIs) were measured at 10 min, 1 h, and 3 h to determine the uptake by papillary cancer. Immunohistopathological staining was performed, and the expression of phospho-ERK MAPK in papillary cancer was investigated. The relation between the expression of phospho-ERK MAPK and the T/B ratio was examined using the Mann-Whitney U-test.

RESULTS

(99m)Tc-tetrofosmin uptake was positive in all patients. There was a statistically significant relation between the T/B ratio (at 3 h) and the expression of phospho-ERK MAPK but not with the T/B ratio at 10 min or 1 h: T/B ratio at 10 min (P = 0.32), at 1 h (P = 0.62), and at 3 h (P = 0.0072).

CONCLUSION

Our results suggest that the relation between (99m)Tc-tetrofosmin uptake (3 h T/B ratio) may lead us to assume cell proliferation of papillary cancer.

64Cu-labeled lissamine rhodamine B: a promising PET radiotracer targeting tumor mitochondria

Enhanced mitochondrial potential in carcinoma cells is an important characteristic of cancer. It is of great current interest to develop a radiotracer that is sensitive to mitochondrial potential changes at the early stage of tumor growth. In this report, we present the synthesis and evaluation of (64)Cu-labeled Lissamine rhodamine B (LRB), (64)Cu(DOTA-LRB) (DOTA-LRB = 2-(6-(diethylamino)-3-(diethyliminio)-3H-xanthen-9-yl)-5-(N-(2-(2-(4,7,10-tris(carboxymethyl)-1,4,7,10-tetraazacyclo-dodecan-1-yl)acetamido)ethyl)sulfamoyl)benzenesulfonate) as a new radiotracer for imaging tumors in athymic nude mice bearing U87MG human glioma xenografts by positron emission tomography (PET). We also explored its localization mechanism using Cu(DOTA-LRB) as the fluorescent probe in both the U87MG human glioma cell line and the cultured primary U87MG glioma cells. It was found that (64)Cu(DOTA-LRB) had the highest tumor uptake (6.54 ± 1.50, 6.91 ± 1.26, 5.68 ± 1.13, 7.58 ± 1.96, and 5.14 ± 1.50%ID/g at 0.5, 1, 2, 4, and 24 h postinjection, respectively) among many (64)Cu-labeled organic cations evaluated in the same animal model. The cellular staining study indicated that Cu(DOTA-LRB) was able to localize in mitochondria of U87MG glioma cells due to the enhanced negative mitochondrial potential. This statement is completely supported by the results from decoupling experiment with carbonylcyanide-m-chlorophenylhydrazone (CCCP). MicroPET data showed that the U87MG glioma tumors were clearly visualized as early as 30 min postinjection with (64)Cu(DOTA-LRB). (64)Cu(DOTA-LRB) remained stable during renal excretion, but underwent extensive degradation during hepatobiliary excretion. On the basis of the results from this study, it was concluded that (64)Cu(DOTA-LRB) represents a new class of promising PET radiotracers for noninvasive imaging of the MDR-negative tumors.

Brain tumour recurrence: brain single-photon emission computerized tomography, PET and proton magnetic resonance spectroscopy

Recurrence is a frequent clinical problem in the follow-up of brain tumours. Single-photon emission computerized tomography, positron emission tomography (PET) and proton magnetic resonance spectroscopy (1H-MRS) represent significant diagnostic options to investigate recurrence. Many authors studied the separate and associate significance of these modalities in investigating relapsing brain tumours. In this study, the current role and the perspectives of these functional diagnostic tools are presented, evidencing the valuable results provided by their association. Finally, future development of new radiopharmaceuticals and advanced MRS technique can reliably contribute to improve the diagnostic process of recurrent brain neoplasms.

Evaluation of brain tumor recurrence by (99m)Tc-tetrofosmin SPECT: a prospective pilot study

OBJECTIVE

The differentiation between brain tumor recurrence and post-irradiation injury remains an imaging challenge. Computed tomography (CT) and magnetic resonance imaging (MRI) cannot always distinguish between the two. Although glioma cell line studies substantiated a plausible imaging superiority of (99m)Tc-tetrofosmin ((99m)Tc-TF) over other radiopharmaceuticals, little has been reported on its in vivo imaging properties. We assessed (99m)Tc-TF single-photon emission CT (SPECT) in cases where morphologic brain imaging was inconclusive between recurrence and radionecrosis.

METHODS

A total of 11 patients (7 men, 4 women) were evaluated. The initial diagnosis was glioblastoma multiforme (4), anaplastic astrocytoma (1), anaplastic oligodendroglioma (3), grade-II astrocytoma (2), and low-grade oligodendroglioma (1). All patients had been operated on and then received adjuvant external-beam radiotherapy. After a mean follow-up period of 25 months, there was clinical suspicion of recurrence, for which (99m)Tc-TF SPECT was performed.

RESULTS

In 8/11 cases, an abnormally increased tracer uptake appeared in the region that CT and/or MRI indicated as suspicious; in half of these cases, recurrence was confirmed histologically after surgery and in the other four by growth of the lesion over a 6-month follow-up period, and clinical deterioration. The remaining 3/11 patients had faint tracer uptake in the suspicious region, compatible with radiation injury; these lesions remained morphologically unaltered in a mean 12-month follow-up period, with no clinical deterioration in the patient's condition, a course strongly favoring the diagnosis of radiation injury.

CONCLUSIONS

Metabolic brain imaging by (99m)Tc-TF could offer useful information in the workup of treated brain tumors, where radiomorphologic findings between recurrence and radionecrosis are inconclusive.

The value of Tc-99m tetrofosmin in the imaging of pituitary adenomas

AIM

Magnetic resonance imaging (MRI) and computerized tomography (CT) are used in the diagnosis and follow-up of pituitary adenoma cases. Sometimes, these methods cannot display the post-operative residual tissue. It has been shown that some radionuclides were taken up by the pituitary adenomas. The aim of this study was to evaluate the uptake of the technetium-99m (Tc-99m) tetrofosmin (TF) in the pituitary adenoma and normal pituitary tissue and assess the ability of Tc-99m TF to predict tumor malignancy in pituitary gland.

METHODS

The patients with pituitary adenoma (7 invasive and 8 non-invasive) were compared with control group (no. 13). Single-photon emission computed tomography (SPECT) imaging of pituitary gland was performed in both groups. Tc-99m uptake indices were evaluated statistically with the use of Mann-Whitney U test.

RESULTS

The average tetrofosmin uptake index of pituitary adenoma is 2.44+/-1.54 for the patients and 1.69+/-0.71 for the control group. Any significant difference was not observed between the groups (p 0.3). The average index was calculated as 3.04+/-2.15 for invasive adenomas and 1.92+/-0.33 for the non-invasive group, and there was no significant difference between the two groups regarding uptake of the agent (p 0.53). Furthermore, it was determined that the invasive and non-invasive adenomas displayed an uptake of Tc-99m TF similar to normal pituitary tissue.

CONCLUSIONS

Since the pituitary adenoma and normal pituitary tissue gave similar results regarding Tc-99m TF uptake, it was concluded that this agent would not be useful in the diagnosis of pituitary adenoma.

Single-Photon Emission Computed Tomography/Computed Tomography in Brain Tumors

Anatomic imaging procedures (computed tomography [CT] and magnetic resonance imaging [MRI]) have become essential tools for brain tumor assessment. Functional images (positron emission tomography [PET] and single-photon emission computed tomography [SPECT]) can provide additional information useful during the diagnostic workup to determine the degree of malignancy and as a substitute or guide for biopsy. After surgery and/or radiotherapy, nuclear medicine examinations are essential to assess persistence of tumor, to differentiate recurrence from radiation necrosis and gliosis, and to monitor the disease. The combination of functional images with anatomic ones is of the utmost importance for a full evaluation of these patients, which can be obtained by means of imaging fusion. Despite the fast-growing diffusion of PET, in most cases of brain tumors, SPECT studies are adequate and provide results that parallel those obtained with PET. The main limitation of SPECT imaging with brain tumor-seeking radiopharmaceuticals is the lack of precise anatomic details; this drawback is overcome by the fusion with morphological studies that provide an anatomic map to scintigraphic data. In the past, software-based fusion of independently performed SPECT and CT or MRI demonstrated usefulness for brain tumor assessment, but this process is often time consuming and not practical for everyday nuclear medicine studies. The recent development of dual-modality integrated imaging systems, which allow the acquisition of SPECT and CT images in the same scanning session, and their co-registration by means of the hardware, has facilitated this process. In SPECT studies of brain tumors with various radiopharmaceuticals, fused images are helpful in providing the precise localization of neoplastic lesions, and in excluding the disease in sites of physiologic tracer uptake. This information is useful for optimizing diagnosis, therapy monitoring, and radiotherapy treatment planning, with a positive impact on patient management.

Usefulness of SPECT/CT with a hybrid camera for the functional anatomical mapping of primary brain tumors by [Tc99m] tetrofosmin

The aims of this study were to assess the clinical usefulness of [Tc-99m] tetrofosmin (TF) single photon emission computed tomography (SPECT) and X-ray transmission computed tomography (CT), performed simultaneously with a hybrid imaging device for the functional anatomical mapping of brain tumors and to evaluate the additional information of SPECT/CT when compared to SPECT alone. Thirty (30) patients were studied: 20 were evaluated before undergoing surgery and 10 after surgery and before radiotherapy planning. The acquisition of both functional (SPECT) and morphologic (CT) images were obtained in a single session. SPECT images were firstly evaluated alone and then reinterpreted by adding the anatomical (CT) planes. Fusion imaging was successfully obtained in all patients with precise correspondence between SPECT and CT slices. SPECT/CT had a significant clinical impact in 13 (43.3%) of 30 cases; in particular, SPECT/CT accurately characterized eight lesions near sites of physiological uptake (i.e., four near ventricles/choroids plexus, three near venous sinuses, one near the skull) and localized viable tumor tissue in 5 patients evaluated after surgery. SPECT/CT with TF using this hybrid device represents a useful clinical tool in brain tumor imaging, both correctly categorizing focal areas near sites of physiological uptake and localizing viable tumor tissue after surgery.

Neuroimaging of Metastatic Brain Disease

This review discusses imaging techniques for the diagnosis, treatment, and monitoring of brain metastases. It assesses the various modalities on the basis of their respective advantages and limitations. Recent advances in imaging technologies provide evaluation that is more accurate for tumor localization, morphology, physiology, and biology. When used in combination, these technologies provide clinicians with a powerful diagnostic and prognostic tool for managing metastatic brain disease.

Study of Monoglutathionyl Conjugates TC-99MSestamibi and TC-99M-Tetrofosmin Transport Mediated by the Multidrug Resistance–Associated Protein Isoform 1 in Glioma Cells

The emergence of multidrug resistance (MDR) is a major obstacle to successful chemotherapy of malignant glioma tumors. Overexpression of the multidrug resistance-associated protein isoform 1 (MRP1), associated with a high level of intracellular glutathione (GSH), is a well-characterized mechanism of MDR in glioma cells. Previously, we have investigated the role of GSH and MRP1 in the accumulation of two radiopharmaceuticals classically used in nuclear medicine: (99m)Tc-sestamibi (MIBI) and (99m)Tc-tetrofosmin (TFOS), in a model of glioma cell lines. Although the involvement of GSH in MRP1-mediated transport of the two radiopharmaceuticals has been demonstrated, the exact transport mechanisms involving phase II (conjugation) and phase III (efflux) detoxification of these lipophilic cations has not been fully elucidated. To clarify the difference of release kinetics observed between MIBI and TFOS, we have studied the efficiency of formation of monogluthationyl conjugates mediated by glutathione S-transferses (GSTs). Our results clearly demonstrate that, in our model, the main efflux mechanism for radiopharmaceuticals is on monoglutathionyl-conjugates of MIBI (MIBI-SG) and TFOS (TFOS-SG). These mechanisms involving MRP1, and the phase II of detoxification is not efficient for TFOS in resistant glioma cells. A relatively slower catalytic efficiency of formation of TFOS-SG conjugate (0.006%.s(-1)) prevents its expulsion, contrary to MIBI (0.133%.s(-1)), suggesting that TFOS should be interesting in the detection and management of patients with high-grade glioma.

Evaluation of Tc99m-glucoheptonate for SPECT functional imaging of medulloblastoma

OBJECTIVES

Functional imaging of medulloblastoma using SPECT has been a difficult problem as this tumour does not concentrate conventional brain tumour imaging radiopharmaceuticals. This study aimed to evaluate Tc99m-glucoheptonate as a "brain tumour-seeking" radiopharmaceutical for functional imaging of medulloblastoma.

METHODS

Tc99m-glucoheptonate brain SPECT was performed in 27 patients with medulloblastoma after radiation therapy and with clinical suspicion of tumour recurrence. Histological verification was obtained within 7 days in patients with a SPECT diagnosis of tumour recurrence. Patients with a SPECT diagnosis of post-radiation gliosis were clinically observed for a minimum period of one year after the SPECT study.

RESULTS

Fourteen patients had increased radiotracer uptake in the primary tumour bed, suggesting tumour recurrence. Histopathology confirmed viable medulloblastoma in all cases. Thirteen patients had no increased tracer uptake in the primary tumour bed, suggesting post-radiation gliosis. They all had a clinical course consistent with post-radiation gliosis.

CONCLUSION

Tc99m-glucoheptonate is an ideal SPECT tracer for functional evaluation of medulloblastoma. SPECT utilising Tc99m-glucoheptonate is a reliable diagnostic modality to differentiate tumour recurrence from post-radiation gliosis in patients with medulloblastoma.

Influence of Glutathione Depletion on Plasma Membrane Cholesterol Esterification and on Tc-99m-Sestamibi and Tc-99m-Tetrofosmin Uptakes: A Comparative Study in Sensitive U-87-MG and Multidrug-Resistant MRP1 Human Glioma Cells

In our previous studies, we demonstrated a possible effect of cellular glutathione (GSH) depletion on plasma-membrane permeability and fluidity in glioma-cell lines. We therefore investigated the effect of GSH modulation on accumulation of two radiotracers, Tc-99m-sestamibi (MIBI) and Tc-99m-tetrofosmin (TFOS), and on plasma-membrane cholesterol content in sensitive U-87-MG and resistant U-87-MG-CIS and U-87-MG-MEL (MRP1 positive) human glioma-cell lines. GSH depletion was mediated by BSO pretreatment and addition of N-acetylcysteine reversed the effect. MIBI and TFOS uptakes, total cholesterol, and cholesteryl-ester contents were evaluated under each condition. In contrast with TFOS, MIBI accumulation was inversely proportional to the cell multidrug resistance phenotype. Similar cholesterol contents were observed in all cell lines, demonstrating that MRP1 did not modify lipid membrane composition. A decrease of intracellular GSH allows an increase of plasma-membrane cholesterol and a decrease of cholesteryl-ester content, which in turn results in spectacular TFOS uptake. The GSH status of the cells plays an important role in the plasma membrane cholesterol composition and TFOS uptake, which appears to be particularly sensitive to this modification. In contrast with MIBI, TFOS is not an MRP1 probe in glioma cells, and therefore appears to be a suitable tracer in this indication.

Microvessel density is not crucial for scintigraphic visualization of brain tumors using 99mTc-MIBI

Functional imaging of brain tumors assists biopsy localization, therapy monitoring, and differentiating tumor recurrence from radiation necrosis. Tumor vascularization is a strong prognostic predictor in solid tumors and also a key factor of tracer uptake. However, the relationship of brain tumor vascularization and functional imaging has not yet been investigated sufficiently so far. In the present study, we correlated histologically assessed microvessel density as an objective parameter for brain tumor vascularization with imaging data. Four male patients were studied. After 99mTc-MIBI scintigraphy, all patients had a MRI within 2 weeks. Histology showed microcystic astrocytoma, glioblastoma (n = 2), and anaplastic oligodendroglioma, respectively. Microvessel density was lowest in the microcystic astrocytoma, medium in the glioblastomas, and highest in the anaplastic oligodendroglioma. Scintigraphy visualized only the glioblastomas, but not the microcystic astrocytoma or oligodendroglioma. Our data showed no correlation between tumor microvessel density and 99mTc-MIBI scintigraphy. Thus, we conclude that scintigraphic visualization of brain tumors is not strictly dependent on tumor vascularization.

Single-photon agents for tumor imaging:201TI,99mTc-MIBI, and99mTc-tetrofosmin

This review aims at fostering comprehension and knowledge not only for expert physicians who can skillfully handle various techniques for tumor imaging but also for young practitioners in the field of nuclear medicine. As image processing software and hardware become smaller, faster and better, SPECT will adapt and incorporate these advances. A principal advantage of SPECT over PET is the more widespread availability of the equipment and lower cost for the introduction of the system in community-based facilities. Moreover, SPECT has become less dependent on a limited number of acknowledged experts for its interpretation owing to a variety of handy computer tools for imaging analyses. The increasing use of PET in tumor imaging is not necessarily proportional to the decline of SPECT. General physicians' attention to SPECT technology would also increase more by evoking their interest in "tracer imaging."

Low uptake of Tc-99m tetrofosmin in lung cancer: a case report

Technetium-99m tetrofosmin has been used as a tumor-imaging agent in cases of lung cancer. The authors present a case showing a lung tumor that concentrated Tl-201 distinctly more than Tc-99m tetrofosmin during a dual-isotope cardiac examination. A brief review of the literature is provided and possible explanations for this difference in tracer uptake are discussed.

The usefulness of 18F-FDG PET images obtained 2 hours after intravenous injection in liver tumor

Liver tumors, especially hepatocellular carcinomas (HCCs), often exhibit no contrast with surrounding non-tumorous liver tissue in F-18-fluoro-2-deoxy-2-fluoro-D-glucose (FDG) positron emission tomography (PET) images obtained at the usual interval of one hour after intravenous FDG injection. We evaluated the usefulness of FDG PET studies of liver tumors performed 2 hours after intravenous injection.

METHODS AND MATERIALS

Fifteen pretherapeutic patients with 33 liver tumors were studied, including 11 patients with 18 HCCs, and 4 patients with 15 metastatic liver tumors (METAs) from 3 colorectal carcinomas and 1 esophageal carcinoma. After transmission scans, emission scans were obtained 45-55 minutes and 115-125 minutes after intravenous injection of 185-370 MBq FDG as early images and delayed FDG PET images, respectively. Visual analysis of early and delayed images was performed, and the FDG uptake in the tumor to that in nontumorous liver ratio (T/N ratio), the FDG uptake in tumor to that in soft-tissue ratio (T/S ratio) and the FDG uptake in non-tumorous liver to that in soft-tissue ratio (N/S ratio) were calculated for each image.

RESULTS

In visual analysis, visual improvement seen in images was observed in 6 of 18 HCC lesions and all 15 META lesions. In quantitative analysis, the mean T/S ratio and T/N ratio of HCCs in early images were 4.97 and 1.90, respectively, and those in delayed images were 6.24 and 2.20, respectively. The mean T/S ratio and T/N ratio of METAs in early images were 5.97 and 2.21, respectively, and those in delayed images were 6.99 and 3.80, respectively. The T/S ratio of HCCs and T/S ratio and T/N ratio of METAs were significantly higher in delayed images than in early images. The mean N/S ratios of HCC cases were 2.58 in the early images and 2.57 in the delayed images, but the ratio showed no constant tendency in the images. All N/S ratios of META cases were decreased in delayed images, although the significance of the difference between early and delayed images in N/S ratios was not analyzed because of the small number of cases.

CONCLUSION

FDG PET studies performed 2 hours after intravenous injection were useful for clear visualization of liver tumors, especially metastatic liver tumors.

Initial evaluation of the feasibility of single photon emission tomography with p-[123 I]iodo-L-phenylalanine for routine brain tumour imaging

p-[123I]iodo-L-phenylalanine (IPA) is a recently described radiopharmaceutical which is highly accumulated in gliomas. The present investigation was designed to evaluate the feasibility of single photon emission tomography (SPET) with IPA to image brain tumours under routine clinical conditions. Using a dual- and a triple-headed SPET camera, whole-body kinetic and brain SPET, as well as plasma, urinary and dosimetric analysis were determined in four patients with gliomas after intravenous injection of IPA. Results obtained by IPA SPET were retrospectively compared with histopathology, magnetic resonance imaging and positron emission tomography with [18F]fluorodeoxyglucose. Tumour lesions were clearly demonstrated by IPA SPET at 30 min, 1h and 4.5h post-injection, even in patients with low grade gliomas. In patients with glioblastoma, excellent visualization of the tumour was possible even at 7h p.i., indicative of the high retention of the radiopharmaceutical in cerebral gliomas. Analysis of the radioactivity in plasma and urine attested to the high in vivo stability of IPA. Blood clearance was rapid (> 65% after 10 min) and IPA was excreted predominantly by the kidneys, the urinary radioactivity excretion ranging from 27% at 1h to 54% of injected doses at 5h p.i. The average effective dose for adults was estimated to be 0.0152mSv*MBq(-1), leading to an effective dose of 3.8mSv in a typical brain SPET investigation with 250 MBq IPA. This result strongly suggests that IPA is a potentially valuable brain tumour imaging agent for widespread clinical studies with SPET. Its high specific tumour uptake and retention even in low grade gliomas represent a major advantage compared to presently available SPET radiopharmaceuticals. Moreover, the radiation dose estimates indicate that clinical use of IPA will result in acceptable radiation dose levels in humans.

New advances in brain tumor imaging

During the period of this review, there has been continued use and development of neuroimaging techniques in brain tumor diagnosis and management. Although no monumental developments or improvements in neuroimaging techniques or technology have occurred, important studies continue to be published showing the clinical impact and utility of various neuroimaging techniques to improve the care of patients with brain tumors. Several studies have shown the power of functional neuroimaging techniques with both magnetic resonance imaging (MRI) and positron-emission tomography (PET) to map eloquent cortex and assist in the planning of surgical and radiation therapy. New nuclear imaging radiopharmaceuticals, including various PET ligands and single photon emission computed tomography (SPECT) agents, have also been developed and show their potential power in the evaluation of brain tumor patients. New MRI pulse sequences to improve image quality and shorten imaging time have also been developed. Several excellent reviews of the use of fluorodeoxyglucose (FDG)-PET and MRI techniques were also published. This article reviews the relevant and important neuroimaging literature related to brain tumor that was published during the defined time period of November 1, 1999 to October 31, 2000. Discussion is organized by modality, including nuclear imaging techniques (SPECT and PET) and MRI (pulse sequence development, contrast agent development, functional MRI developments, and general MRI-related information).