Comparison of technetium-99m methoxyisobutylisonitrile and gallium-67 citrate scanning in the assessment of lymphomas

Applications of 99mTC-Sestamibi in Oncology

Hexakis (2-methoxyisobutylisonitrile) technetium-99m (99mTc-SestaMIBI) is a radiopharmaceutical used in nuclear medicine for myocardial perfusion imaging. In the literature different non-cardiac applications of 99mTc-SestaMIBI have been reported. Clinical studies have been performed also in non-oncologic diseases (such as thyroid adenoma, diabetic foot, osteomyelitis, pulmonary actinomycosis, aneurysmal bone cyst, Sudeck's atrophy). Several models for the uptake mechanism of this radiopharmaceutical have been proposed such as binding to an 8-10 kDa cytosolic protein, simple lipid partitioning, or a membrane translocation mechanism involving diffusion and passive transmembrane distribution. Most evidence points in the direction of the third hypothesis. Many studies have indicated that uptake of hexakis (alkylisonitrile) technetium complexes is dependent on mitochondrial and plasma membrane potentials like other lipophilic cations. This explains the initial biodistribution of 99mTc-SestaMIBI to tissues with negative plasma membrane potentials and with a relatively high mitochondrial content (like heart, liver, kidney and skeletal muscle tissue). Malignant tumours also possess these properties in order to maintain their increased metabolism. This behaviour encouraged the study of 99mTc-SestaMIBI as an interesting tracer imaging various tumour types: osteosarcoma, brain, lung, breast, nasopharyngeal, parathyroid, and thyroid cancer. Recent research on cell cellular physiology has further revealed an active transport of 99mTc-SestaMIBI out of the tumour cells, against the potential gradient. The same mechanism is also responsible for resistance to a structurally and functionally different group of cytotoxic agents, such as vinca alkaloids, epipodophyllotoxins, anthracyclins and actinomycin D. This peculiar type of resistance is due to amplification of the mammalian MDR1 gene, located on chromosome 7. For this reason the 99mTc- SestaMIBI uptake in vivo could permit the prediction of the response to the chemotherapy, when the decreased accumulation of 99mTc-SestaMlBI implies the presence of P-gp enriched tissues. In the next future a particular attention should be dedicated to this matter since one of the most important goals of the clinical trials is the demonstration of the usefulness of 99mTc-SestaMIBI for in vivo assessment of multidrug resistance.

99mTechnetium-SESTAMIBI Uptake in Malignant Lymphomas. Correlation with Chemotherapy Response

BACKGROUND

The rationale of the present study is based on the property of technetium-SESTAMIBI to enter malignant and other highly metabolic cells, and then to be pumped out of them by the multidrug-resistant (MDR) system, strongly depending on the expression of the MDR-1 gene encoded P-glycoprotein (Pgp-170).

METHODS AND RESULTS

Forty-one patients with malignant lymphoma were studied before chemotherapy. Images were taken 30 min (early) and 180 min (late) after intravenous injection of (99m)Tc-MIBI, and then visually interpreted. They were correlated with clinical response defined as chemosensitive (ChS) when a >6 month remission was attained, and chemoresistant (ChR) to any other response. Of 41 patients, 27 had an early positive uptake, 18 (67%) were ChS, and 9 (33%) ChR. Of these 27 patients, 19 also had late positive scans; 15 (79%) were ChS, and only 4 were ChR (p = 0.037). Conversely, 10 of 14 remaining patients with negative early scans were ChR. Eight patients had an early positive study; however, the late retention of (99m)Tc-MIBI was negative and the relationship to chemotherapy response was not conclusive. A breakdown of data was made according to histology. Patients with low grade lymphoma had the strongest correlation between (99m)Tc-MIBI uptake and chemosensitivity. Patients with high grade lymphoma had only a trend, and patients with Hodgkin's disease had an indefinable correlation.

CONCLUSIONS

This study takes advantage of the relationship between the ability to uptake and retain (99m)Tc-MIBI, a Pgp-170 substrate, by lymphomatous tumors. This attribute, combined with other clinical data, could help to select tailored treatments for patients that are likely to be chemoresistant before treatment.

Noncardiac findings on dual-isotope myocardial perfusion SPECT

BACKGROUND

This study examined the frequency of reporting noncardiac findings (NCFs), such as malignancies from inspection of raw projection images with dual-isotope single photon emission computed tomography (SPECT) perfusion imaging, which could potentially be of greater clinical importance than myocardial perfusion imaging alone. Dual-isotope (ie, rest thallium 201 and stress technetium 99m sestamibi [MIBI] or Tc-99m tetrofosmin [TET]) SPECT myocardial perfusion imaging combines multipotential tracers for noncardiac purposes (Tl-201 for renal or splenic imaging, inflammation, or lymphoma and MIBI or TET for hepatobiliary imaging and detecting increased mitochondrial number or activity in neoplastic processes). These images are optimally interpreted with cinematic inspection of the raw projection data, but this may not be practiced uniformly in every laboratory.

METHODS AND RESULTS

We reviewed 12,526 computer-generated text reports of dual-isotope perfusion SPECT studies from a 6-year period for NCFs. NCFs were categorized by organ and by probability of malignancy: high (eg, focal breast or lung uptake of MIBI or TET), intermediate (eg, lymph node uptake or thyroid abnormalities), or low (eg, filling defects in liver, kidney, spleen, or gall bladder; ascites; or pleural effusions). Confirmatory imaging studies or clinical confirmation for each NCF was sought. There were a total of 207 NCFs identified in 180 reports (1.7% of reports, ranging from 0% to 2.8% of reports of individual interpreters). Of these, 107 NCFs were unsuspected before SPECT; 24% were considered at high probability for malignancy, and 24% were considered intermediate in likelihood of malignancy. Follow-up data were available for 178 NCFs, confirming 88% of these findings, including 82% of breast foci, 62% of lung foci, 86% of hepatobiliary/spleen abnormalities, and 94% of renal abnormalities. The probability of malignancy was highest (82%) in breast or lung foci in which uptake of both Tl-201 and the Tc-99m-labeled agent was present.

CONCLUSIONS

In patients referred for evaluation of myocardial perfusion, NCFs are unusual and require systematic and careful inspection of projection images for their detection. With Tl-201, TET, MIBI, or dual-isotope imaging, detecting and reporting NCFs may occasionally result in life-saving early cancer identification.

Gallium-67 scintigraphy: a cornerstone in functional imaging of lymphoma

Until recently, gallium-67 scintigraphy (GS) has been the best available functional imaging modality for evaluating patients with non-Hodgkin's lymphoma (NHL) and Hodgkin's disease (HD). The diagnostic accuracy of GS in detecting lymphoma is based on optimisation of the imaging protocol, knowledge of potential physiological and benign sites of (67)Ga uptake, and the Ga avidity characteristics of the individual lymphoma. As (67)Ga is a tumour viability agent, the role of GS is primarily at follow-up. A residual mass persisting on CT after treatment poses a common clinical dilemma: it may indicate the presence of viable lymphoma, which requires further treatment, or it can be benign, consisting of only fibrotic and necrotic tissues. GS can successfully differentiate between these conditions. Routine follow-up with GS may allow early diagnosis of recurrence and early institution of treatment. Reversion of a positive GS to a negative test, and the rapidity with which this occurs has a high predictive value for the outcome of the individual patient. Lymphoma showing a normal GS early during treatment has a better prognosis than lymphoma with persistence of pathological findings. Other tumour-seeking single-photon emitting agents, such as thallium-201, technetium-99m methoxyisobutylisonitrile and indium-111 octreotide, have been investigated in lymphoma, primarily as an alternative to GS in specific clinical settings, but are of limited value. The role of radioimmunoscintigraphy is gaining importance in conjunction with radioimmunotherapy. Fluorine-18 fluorodeoxyglucose (FDG) imaging of lymphoma using either dedicated or camera-based PET systems is gradually replacing GS for assessment of lymphoma. FDG overcomes some of the limitations of GS while sharing its tumour viability characteristics. The extensive clinical knowledge and experience accumulated over three decades with GS in lymphoma provides a solid background as well as a model for the assessment of new functional imaging techniques.

Technetium-99m Tetrofosmin Imaging in Malignant Lymphomas

Aim

To assess the utility of 99mTc tetrofosmin (TF) scintigraphy as a diagnostic modality in lymphomas.

Methods

Seventeen patients (14 with Hodgkin's disease and three with non-Hodgkin's lymphomas; age range, 10-59 years) were investigated. Planar and SPECT images of the supradiaphragmatic region (including neck and chest) were obtained. All patients were untreated at the time of the first scintigraphy. Follow-up scans after therapy were acquired in six patients (in five twice), so a total of 28 scintigraphic studies were performed. Mediastinal, pulmonary, cervical, supraclavicular and axillary activity was evaluated and results were compared in a blinded fashion with those of CT.

Results

TF imaging demonstrated pathological focal uptake at 38 sites (16 in the mediastinum, eight in the lungs, four in the axillae, eight in the supraclavicular region and two in the cervical region) in 16 of 17 untreated patients; CT identified 24 lesions (16 in the mediastinum, two in the lungs, two in the axillae, two in the supraclavicular and two in the cervical region) in 17 patients. Scintigraphy detected 22 of the 24 lesions demonstrated by CT and revealed 16 unknown tumor sites in 10 patients. The only negative pre-treatment scintigraphy result was found in a patient with axillary lymph node involvement. On the first post-treatment scintigrams there was a reduction in the number of visualized pathological sites (seven vs 16) in five of the six patients examined. The second follow-up study demonstrated only two lesions in two of the five patients examined.

Conclusions

Our preliminary results indicate that TF imaging is effective in depicting supradiaphragmatic lymphoma lesions in untreated patients and suggest that serial scintigraphic studies may be suitable for monitoring response to treatment. However, larger series are needed to better define the possible role of TF scintigraphy in the follow-up of the response to therapy.

Radionuclide evaluation of patients with lymphoma

Nuclear medicine imaging techniques allow us to peer into physiologic processes, avoiding the need to wait until anatomic changes are detectable, and allowing for prompt, informed management decisions. Recognition of normal, abnormal, and post-therapy scan patterns is critical to achieve the necessary sensitivity and specificity needed for patient management. Gallium scintigraphy using updated techniques has an important continuing role in management of patients with lymphoma. Gallium scintigraphy can contribute to patient management primarily by detecting residual disease or relapse after treatment, monitoring response during therapy, and providing prognostic information. FDG and PET cameras, especially dedicated ring systems, offer high resolution and high-contrast images, thereby demonstrating additional sites of disease. Although preliminary evidence looks promising that FDG can provide all information that Ga-67 has been shown to do in the past, additional data are required. Further studies will show whether FDG-PET can provide prognostic information and predict disease-free and overall survival, the availability of both FDG and PET scanners, and issues of cost. Patient accessibility will undoubtedly also play a role in when, or whether, FDG-PET will totally replace Ga-67 scintigraphy in the management of patients with lymphoma.

Accumulation of sestamibi in lymphoma cell lines in vitro

Although some authors have suggested that sestamibi imaging is useful in evaluation of patients with lymphoma, others have obtained equivocal results. This discrepancy has been further investigated in vitro using two patient-derived non-Hodgkin's lymphoma cell lines, OCI-Ly3 and OCI-Ly18. Sestamibi (0.2 MBq/ml) was added to a suspension of OCI-Ly3 or OCI-Ly18 cells and aliquots were removed over 1 h and centrifuged to determine cell-associated radioactivity. Further experiments studied the effect of addition of a P-glycoprotein (Pgp) modulator or alteration in plasma and/or mitochondrial membrane potentials. Accumulation of sestamibi reached plateau values within 30 min, but these values were 6-fold higher in OCI-Ly3 than in OCI-Ly18. Inhibition of Pgp function with GG918 or PSC833 did not affect OCI-Ly3 cells but increased accumulation in OCI-Ly18 cells 3-fold, indicating a moderate level of Pgp. However, both cell lines responded similarly to membrane potential alterations: hyperpolarization of the mitochondrial membrane with nigericin had little effect on accumulation: in contrast, depolarization of the plasma membrane with an isotonic high potassium buffer reduced accumulation of sestamibi to 52% of control and additional depolarization of the mitochondrial membrane with valinomycin further reduced accumulation to 12% of control levels. These studies suggest that there can be wide differences in accumulation between cell lines, in part due to Pgp-mediated efflux, but that both of these cell lines have highly polarized mitochondria with little further capacity for hyperpolarization.

Uptake of 99mTc-tetrofosmin, 99mTc-MIBI and 201Tl in malignant thymoma

99mTc-tetrofosmin, Thallium-201-chloride (201Tl) and 99mTc-MIBI imagings were performed in a patient with malignant thymoma. Tracer uptake in the primary tumor was demonstrated. The tumor-to-background ratios of planar and SPECT imagings were 1.60 and 1.98 for 99mTc-tetrofosmin, 1.12 and 2.09 for 201Tl, and 1.19 and 1.80 for 99mTc-MIBI, respectively. In another patient 99mTc-tetrofosmin and 201Tl imagings were performed. Not only the primary tumor but also the direct invasions and metastatic lesions (bone metastases) were clearly detected. The tumor-to-background ratios of planar and SPECT imagings were 2.31 and 2.78 for 99mTc-tetrofosmin and 2.45 and 3.58 for 201Tl, respectively. In 99mTc-tetrofosmin scintigraphy we acquired delayed images, and the tumor-to-background ratios of planar and SPECT delayed images were 1.20 and 1.86, the retention ratios were -1.11 and -0.92 and the retention indices were -48.1 and -33.1, respectively. Our preliminary results suggest that 99mTc-tetrofosmin is useful in detecting not only the primary tumor but also metastatic lesions from malignant thymoma.

Gallium scan in the evaluation of post chemotherapy mediastinal residual masses of aggressive non-Hodgkin's lymphoma

Optimal evaluation of residual masses of non Hodgkin's lymphomas (NHL) after chemotherapy is of major importance, and gallium scan (GS) is routinely used for this purpose, particularly for mediastinal sites. However, sensitivity and specificity of GS in this setting has been diversely appreciated and needs to be more accurately defined especially if radiotherapy is not planned. A retrospective analysis selected all the patients treated in a single institution for aggressive NHL who presented a residual mass in the mediastinum after chemotherapy and who were evaluated by GS. The value of GS for distinguishing true complete responses (CR) from partial responses (PR) was analyzed in patients who were either submitted to resection of their residual mass or followed up without further treatment after GS. A residual mass with mean perpendicular diameters measuring 4.1 cm x 2.8 cm was found in 42 patients and was GS positive in 8 cases and negative in 34 cases. After GS, radiotherapy was delivered to 10 patients, but 12 patients underwent resection of their residual mass and 20 were followed up without further treatment. In the patients who did not receive radiotherapy, 3 false positive and 6 false negative GS results were disclosed. The specificity and the sensitivity of GS were 88% and 25%, and its positive predictive value and negative predictive value 40% and 78%, respectively. GS was not sufficiently reliable to evaluate post chemotherapy residual masses. Surgical resection of residual masses should be considered particularly in young patients. Patients in true CR should be spared pointless radiotherapy and its late side effects, while patients in PR may benefit from further intensified chemotherapy followed by radiotherapy.

Visualisation of a paraganglioma by technetium-99m-sestamibi scintigraphy

A 68-yr-old woman presented to our observation with multinodular goiter and a contiguous right laterocervical mass. In spite of ultrasound, technetium and iodine scan, CT and fine-needle biopsy, the precise origin of the mass remained uncertain. On additional multi-phase sestamibi scan, the neck region showed an early high uptake rapidly decreasing over time in the laterocervical mass, and a persistent inhomogeneous distribution in the thyroid gland. This behavior suggested that the laterocervical mass could derive from an anatomical structure other than the thyroid. Surgical exploration established the extrathyroid nature of the laterocervical mass and the histological examination confirmed that it was a typical paraganglioma. This finding is in keeping with a recent report of positive sestamibi uptake in a cervical paraganglioma, although our case showed a more rapid kinetic. This tumor should be therefore taken into consideration in the differential interpretation of focal sestamibi uptake.

[125I/127I/131I]Iodorhodamine: synthesis, cellular localization, and biodistribution in athymic mice bearing human tumor xenografts and comparison with [99mTc]hexakis(2-methoxyisobutylisonitrile)

The synthesis of halogenated rhodamine (Rh) derivatives was carried out by controlling the stoichiometry of the halogenating agents, bromine and iodine monochloride. In the no-carrier-added synthesis of radioiodinated rhodamine 123, direct labeling of rhodamine 123 (Rh 123) with Na125I/Na131I required the presence of the oxidant peracetic acid. 125I/131I-Rh 123 was synthesized in modest yields (40-45%). HPLC purification separated Rh 123 from its mono- and diiodo derivatives. Monohalogenation of Rh 123 did not alter the compound's ability to permeate viable cells and localize in mitochondria. 125I/131I-Rh 123 was stable in serum in vitro but rapidly metabolized after intravenous injection into mice. Consequently, scintigraphy and biodistribution data reveal poor targeting of subcutaneously growing human tumor xenografts. The results are compared to those obtained following the administration of [99mTc]hexakis(2-methoxyisobutylisonitrile) which also did not image human tumor xenografts in nude mice.

Tc-99m sestamibi imaging in the diagnostic assessment of patients with lymphomas: comparison with clinical and radiological evaluation

Tc-99m MIBI imaging has been used in nuclear oncology, but its role in detecting lymphomas has not been widely investigated. In this study, 31 patients with lymphomas (20 non-Hodgkin's and 11 Hodgkin's) underwent Tc-99m MIBI whole-body imaging. A total of 74 tumor lesions were detected in 25 patients, while the remaining 6 patients were disease-free. The diagnostic accuracy of MIBI imaging for lesion detection was 85%. A total of 11 unknown tumor lesions in 3 patients were discovered on MIBI scans. Tumor size was significantly (p = 0.01) higher in lesions with increased MIBI uptake (3.5 +/- 2.0 cm) compared with those with no uptake (1.8 +/- 1.0 cm). No false positive MIBI findings were observed. The accuracy of MIBI scintigraphy in patients with Hodgkin's disease was lower (72%) compared to that of patients with non-Hodgkin's lymphomas (94%). However, this difference was not related to tumor type, but to lesion size. In fact, tumor size was significantly (p = 0.02) lower in lesions of patients with Hodgkin's disease (2.5 +/- 1.3 cm) compared to those of patients with non-Hodgkin's lymphomas (3.7 +/- 2.2 cm). MIBI imaging may be useful in patients with lymphomas for detecting tumor lesions and, hence, may be considered an alternative to gallium scanning, providing better imaging quality. However, the intense Sestamibi activity in the lower chest and abdomen as well as tumor size may limit the diagnostic sensitivity of this radionuclide technique in patients with lymphomas.

Use of 99mTc-MIBI scintigraphy in the evaluation of the response of osteosarcoma to chemotherapy

The use of gamma camera scintigraphy with technetium-99m hexakis-2-methoxyisobutylisonitrile (99mTc-MIBI) for assessment of the response of high-grade osteosarcoma to preoperative chemotherapy was evaluated. Twelve patients with osteosarcoma of the extremities underwent planar examination with 99mTc-MIBI before and after preoperative chemotherapy according to the recommendations of the Scandinavian Sarcoma Group. After calculating a quotient for the tumour and the average activity of both extremities and correcting for background activity, the change in uptake between the two examinations was assessed. This was compared with histological examination of the ultimately resected specimen in 11 patients and progressive clinical disease in one. All the 11 tumours undergoing histological examination showed cellular necrosis of between 50% and 100% as well as a reduced uptake of 99mTc-MIBI, while the single progressive tumour showed an increased uptake. There was a correlation between the reduction of radiopharmaceutical uptake and the histological response in the entire series, while the variation was too large to allow conclusions in individual patients. This variation may have biological reasons or may be due to the planar imaging technique, which only allows semiquantitative evaluation. The technique reflects response to therapy but is not yet clinically applicable for the identification of poor responders, which would serve as a basis for alteration of the chemotherapy regimen. In order to evaluate whether such a role could be fulfilled, further studies using single-photon emission tomography with correction for attenuation and scattering of photons are necessary.

Tc-99m MIBI scintigraphy in patients with lung cancer. Comparison with CT and fluorine-18 FDG PET imaging

Tc-99m MIBI imaging has been used to evaluate patients with different neoplastic disorders, but its role in nuclear oncology has not been definitely established. In this study, we compared the results of Tc-99m MIBI (planar and SPECT imaging) with those of F-18 FDG PET radionuclide studies in 19 patients who had proven lung cancer. One patient was studied in follow-up. All patients underwent chest CT scans. MIBI and FDG images were qualitatively and quantitatively analyzed using region of interest analysis. Quantitative evaluation of MIBI and FDG activities in lung-tumor lesions was performed calculating tumor/nontumor ratios. On CT, 18 lung tumors were detected, while one patient was disease free. For lung lesions, the diagnostic sensitivity of planar MIBI imaging was 83%, while those of MIBI SPECT and FDG PET were both 100%. The quantitative analysis of lung-tumor MIBI and FDG activities showed that FDG uptake was significantly (P < 0.001) higher compared with MIBI uptake (5.5 +/- 3.1 vs 2.1 +/- 0.6); concordant MIBI and FDG images were found in 4 lesions in terms of central activity defect showing central necrotic tumor tissue. For lymph node abnormalities, planar MIBI scan only detected 3 lesions in 3 patients, whereas MIBI SPECT identified 9 lesions in 5 patients. FDG PET showed 13 lymph node abnormalities in 5 patients. This study shows similar results of Tc-99m MIBI SPECT and F-18 FDG PET in the diagnostic evaluation of patients with lung tumors. However, FDG lung tumor uptake was significantly higher compared with MIBI accumulation, suggesting a high glucose tumor metabolism. Thus, MIBI SPECT imaging may be useful to evaluate such patients and may be considered an alternative when PET is not available.

Accumulation of 99mTc-MIBI in bone marrow

99mTc-MIBI (Sestamibi) was originally developed for myocardial perfusion studies. The agent also may be used for the depiction and characterization of tumors. Performing such examinations has shown uptake in skeletal structures in several patients suggesting bone engagement of the disease which later was excluded. Retrospective evaluation of 44 examinations with 99mTc-MIBI performed in order to localize diseased parathyroid in patients with suspected hyperparathyroidism showed skeletal activity in 21 (48%) patients. Although these patients represent a selected group, the observation indicates a mechanism for skeletal accumulation of this radiopharmaceutical. Evaluation of another 13 normocalcemic patients undergoing whole-body registration for malignancy staging or to assess lower extremity ischemia with 99mTc-MIBI showed skeletal activity in 6 (46%) patients. Complementary mouse experiments confirmed skeletal uptake of 99mTc-MIBI, where most of the activity is taken up by the red bone marrow. It is concluded that homogeneous, diffuse weak skeletal activity at examination with 99mTc-MIBI is a normal finding and does not indicate malignancy.

Sweat glands accumulate Tc-99m MIBI

Tc-99m MIBI, which was originally developed for myocardial perfusion studies, may also be used for depiction and characterization of tumors. Forty-one patients with suspected hyperparathyroidism were examined with Tc-99m MIBI to localize a parathyroid adenoma or hyperplasia. In 19 of these patients (46%), bilateral symmetrical activity corresponding to the large deep apocrine sweat glands of the axillae was present. Sweat gland activity was not correlated with serum calcium levels. Although these patients may represent a selected group, the observation is clinically relevant regardless of its reason or mechanism. It is important also to be aware of this cause for activity in the axilla when assessing lymph node involvement in breast cancer patients using Tc-99m MIBI.