Presurgical 99mTc-sestamibi brain SPET/CT versus SPET: a comparison with MRI and histological data in 33 patients with brain tumours

Clinical usefulness of 99mTc-HYNIC-TOC, 99mTc(V)-DMSA, and 99mTc-MIBI SPECT in the evaluation of pituitary adenomas

Background

The aim of this study was to evaluate the behavioral uptake and ability to diagnose pituitary adenoma (PA) using tumor-seeking radiopharmaceuticals, and to provide a semiquantitative analysis of tracer uptake in the pituitary region.

Patients and methods

The study included 33 (13 hormonally active and 20 nonfunctioning) patients with PA and 45 control participants without pituitary involvement. All patients (n=78) underwent single photon emission computed tomography (SPECT) imaging with technetium-99m-labeled hydrazinonicotinyl-tyr³-octreotide (^99mTc-HYNIC-TOC), dimercaptosuccinic acid (^99mTc(V)-DMSA) and hexakis-2-methoxyisobutylisonitrile (^99mTc-MIBI). A semiquantitative analysis of abnormal uptake was carried out by drawing identical regions of interest over the pituitary area and the normal brain on one transverse section that shows the lesion most clearly. The pituitary uptake to normal brain uptake (P/B) ratio was calculated in all cases.

Results

The result of this study confirms that the SPECT semiquantitative method, with all three tracers, showed statistically significant differences between the PA group and the controls. However, ^99mTc-HYNIC-TOC scintigraphy could have the highest diagnostic yield because of the smallest overlap between the P/B ratios between adenoma versus nonadenoma participants (the receiver operating characteristic curve P/B ratio cut-off value was 13.08). In addition, only ^99mTc-MIBI SPECT have the diagnostic potential to detect secreting PAs, with statistically significant differences between groups (P<0.001), with an receiver operating characteristic curve P/B ratio cut-off value of 16.72.

Conclusion

A semiquantitative analysis of increased focal tracer uptake in the sellar area showed that ^99mTc-HYNIC-TOC is a highly sensitive and reliable tumor-seeking agent for detecting PA, whereas ^99mTc-MIBI SPECT is a highly sensitive and specific method in differentiating hormone-secreting pituitary tumor.

The effect of regadenoson on the integrity of the human blood-brain barrier, a pilot study

Regadenoson is an FDA approved adenosine receptor agonist which increases blood-brain barrier (BBB) permeability in rodents. Regadenoson is used clinically for pharmacologic cardiac stress testing using SPECT or CT imaging agents that do not cross an intact BBB. This study was conducted to determine if standard doses of regadenoson transiently disrupt the human BBB allowing higher concentrations of systemically administered imaging agents to enter the brain. Patients without known intracranial disease undergoing clinically indicated pharmacologic cardiac stress tests were eligible for this study. They received regadenoson (0.4 mg) followed by brain imaging with either ^99mTc-sestamibi for SPECT or visipaque for CT imaging. Pre- and post-regadenoson penetration of imaging agents into brain were quantified [SPECT: radioactive counts, CT: Hounsfield units (HU)] and compared using a matched-pairs t-test. Twelve patients (33% male, median 60 yo) were accrued: 7 SPECT and 5 CT. No significant differences were noted in pre- and post-regadenoson values using mean radionuclide counts (726 vs. 757) or HU (29 vs. 30). While animal studies have demonstrated that regadenoson transiently increases the permeability of the BBB to dextran and temozolomide, we were unable to document changes in the penetration of contrast agents in humans with intact BBB using the FDA approved doses of regadenoson for cardiac evaluation. Further studies are needed exploring alternate regadenoson dosing, schedules, and studies in patients with brain tumors; as transiently disrupting the BBB to improve drug entry into the brain is critical to improving the care of patients with CNS malignancies.

Assessing response using 99mTc-MIBI early after interstitial chemotherapy with carmustine-loaded polymers in glioblastoma multiforme: preliminary results

Introduction. Early signs of response after applying wafers of carmustine-loaded polymers (gliadel) are difficult to assess with imaging because of time-related imaging changes. (99m)Tc-sestamibi (MIBI) brain single-photon emission tomography (SPET) has reportedly been used to reveal areas of cellularity distinguishing recurrent neoplasm from radionecrosis. Our aim was to explore the role of MIBI SPET in assessing response soon after gliadel application in glioblastoma multiforme (GBM). Methods. We retrospectively reviewed the charts on 28 consecutive patients with a radiological diagnosis of GBM who underwent MIBI SPET/CT before surgery (with intracavitary gliadel placement in 17 patients), soon after surgery, and at 4 months. The area of uptake was selected using a volume of interest that was then mirrored contralaterally to obtain a semiquantitative ratio. Results. After adjusting for ratio at the baseline, the effect of treatment (gliadel versus non-gliadel) was not statistically significant. Soon after surgery, however, 100% of patients treated with gliadel had a decreased ratio, as opposed to 62.5% of patients in the non-gliadel group (P = 0.0316). The difference between ratios of patients with radical versus partial resection reached statistical significance by a small margin (P = 0.0528). Conclusions. These data seem to suggest that the MIBI ratio could be a valuable tool for monitoring the effect of gliadel early after surgery.

Less commonly used and emerging clinical applications of SPECT-CT in benign and malignant disease

The emergence of hybrid imaging, combining anatomical computed tomography (CT) and functional single-photon emission computed tomography (SPECT), has greatly expanded the armoury available to image disease. Integrated SPECT-CT is a dual-modality technique, which improves the sensitivity and specificity of existing radionuclide studies and enables characterization of equivocal findings detected by conventional imaging. There is a wide range of established and emerging clinical applications for SPECT-CT, which were reviewed in detail at a symposium organized by the British Institute of Radiology in March 2012. A series of articles were commissioned as an adjunct to the symposium and to raise awareness of the clinical utility of this technique. The focus of this article is on less commonly used and emerging clinical applications of hybrid SPECT-CT in a spectrum of benign and malignant conditions. The article will illustrate the incremental value of the technique in a variety of clinical applications.

Investigation of blood perfusion and metabolic activity of brain tumours in adults by using 99mTc-methoxyisobutylisonitrile

OBJECTIVES

(i) To examine blood perfusion and metabolic activity of various brain tumours using radionuclide cerebral angiography (RCA) and single-photon emission tomography (SPET) after a single dose of Tc-methoxyisobutylisonitrile (MIBI). (ii) To examine if the inclusion of RCA can improve insight into the relative contribution of tumour perfusion to the uptake of MIBI shown by SPET, and to improve evaluation of tumour biology. (iii) To determine the value and the roles of MIBI in the management of brain tumour patients.

METHODS

Fifty adult patients (38 male, 12 female) with a total of 56 intracranial space-occupying lesions have been included prospectively, 37 of which were newly diagnosed and the remaining with signs of recurrence/rest of earlier resected and irradiated brain tumours. The control group consisted of nine volunteers with no evidence of organic cerebral disease. Scintigraphic examination consisted of a dynamic first-pass study lasting 60 s (3 s/frame) and two SPET studies (60 projections each, 25 s/projection), starting 15 min and 2 h after intravenous injection of MIBI. Regions of interest of the tumour and normal brain tissue were drawn on RCA and both early and delayed SPET slices. The following tumour/brain activity ratios have been calculated: (i) tumour perfusion index (P); (ii) early uptake index (E); (iii) delayed uptake index (D); and(iv) retention index (R). Analogous indices have been calculated from the same examinations performed in controls, reflecting maximal physiologic regional variations of perfusion and uptake in brain tissue.

RESULTS

Mean P of various brain tumours (low-grade gliomas 0.98, anaplastic gliomas 1.14, glioblastoma multiforme 1.20, metastases 1.09, lymphomas 1.08) differ little from each other and do not exceed maximal physiologic regional variations of cerebral perfusion (1.33), with the exception of meningioma (1.87, F=2.83, P=0.015). The receiver operating characteristics curve analysis of P showed that for the cut-off value of 1.45 the sensitivity for distinguishing meningioma from other tumours is 75%, specificity 87%, positive predictive value 33% and negative predictive value 97%. Mean E of malignant brain tumours (8.3, n=31, 23 primary, eight secondary), except anaplastic gliomas (3.5, n=5), differed significantly (P=0.02) from those of benign gliomas (3, n=9) but not from that of meningioma (11.9, n=4). The cut-off value for distinguishing malignant from benign lesions on the basis of E set at 4.8 resulted in sensitivity 67%, specificity 75%, accuracy 70%, positive predictive value 80% and negative predictive value 60%. D and R showed tendency of wash-out of MIBI from meningiomas, but otherwise did not improve the results substantially.

CONCLUSION

Integrated results of RCA and SPET with Tc-MIBI indicate that blood perfusion, blood-tumour barrier permeability and metabolic activity of the tumour are all very important for the resultant uptake shown by SPET. If the perfusion index is less than 1.45, then meningioma can be ruled out. Early SPET is recommendable for distinguishing glioblastoma from low-grade gliomas, as a complement to standard magnetic resonance imaging and/or computed tomography.