Biodistribution of Tc-99m methoxy-isobutyl-isonitrile (MIBI) in humans

Phase I, first-in-human study of XTR004, a novel 18F-labeled tracer for myocardial perfusion PET: Biodistribution, radiation dosimetry, pharmacokinetics, and safety after a single injection at rest

OBJECTIVES

This study assessed the imaging characteristics, pharmacokinetics and safety of XTR004, a novel 18F-labeled Positron Emission Tomography (PET) myocardial perfusion imaging tracer, after a single injection at rest in humans.

METHODS

Eleven healthy subjects (eight men and three women) received intravenous XTR004 (239-290 megabecquerel [MBq]). Safety profiles were monitored on the dosing day and three follow-up visits. Multiple whole-body PET scans were conducted over 4.7 h to evaluate biodistribution and radiation dosimetry. Blood and urine samples collected for 7.25 h were metabolically corrected to characterize pharmacokinetics.

RESULTS

In the first 0-12 min PET images of ten subjects, liver (26.81 ± 4.01), kidney (11.43 ± 2.49), lung (6.75 ± 1.76), myocardium (4.72 ± 0.67) and spleen (3.1 ± 0.84) exhibited the highest percentage of the injected dose (%ID). Myocardial uptake of XTR004 in the myocardium initially reached 4.72 %ID and 7.06 g/mL, and negligibly changed within an hour (Δ: 7.20%, 5.95%). The metabolically corrected plasma peaked at 2.5 min (0.0013896 %ID/g) and halved at 45.2 min. Whole-body effective dose was 0.0165 millisievert (mSv)/MBq. Cumulative urine excretion was 8.18%. Treatment-related adverse events occurred in seven out of eleven subjects (63.6%), but no severe adverse event was reported.

CONCLUSIONS

XTR004 demonstrated a favorable safety profile, rapid, high, and stable myocardial uptake and excellent potential for PET myocardial perfusion imaging (MPI). Further exploration of XTR004 PET MPI for detecting myocardial ischemia is warranted.

Dose-consistent dynamic SPECT

BACKGROUND

Coronary flow reserve (CFR) values measured by dynamic SPECT systems are typically consistent with other modalities (e.g., PET). However, large discrepancies are often observed for individual patients. Positioning of the region-of-interest (ROI), representing the arterial input function (AIF) could explain some of these discrepancies. We explored the possibility of positioning the ROI in a manner that evaluates its consistency with patient-based injected radiotracer doses.

METHODS

Dose-consistent dynamic SPECT methodology was introduced, and its application was demonstrated in a twenty-patient clinical study. The effect of various ROI positions was investigated and comparison to myocardial perfusion imaging was performed.

RESULTS

Mean AIF ratios were consistent with the injected dose ratios for all examined ROI positions. Good agreement (> 80%) between total perfusion deficit and CFR was found in the detection of obstructive CAD patients for all ROIs considered. However, for individual patients, significant dependence on ROI position was observed (altering CFR by typically 30%). The proposed methodology's uncertainty was evaluated (~ 7%) and found to be smaller than the variability due to choice of ROI position.

CONCLUSION

Dose-consistent dynamic SPECT may contribute to evaluating uncertainty of CFR measurements and may potentially decrease uncertainty by allowing improved ROI positioning for individual patients.

Parathyroid Imaging: Past, Present, and Future

The goal of parathyroid imaging is to identify all sources of excess parathyroid hormone secretion pre-operatively. A variety of imaging approaches have been evaluated and utilized over the years for this purpose. Ultrasound relies solely on structural features and is without radiation, however is limited to superficial evaluation. 4DCT and 4DMRI provide enhancement characteristics in addition to structural features and dynamic enhancement has been investigated as a way to better distinguish parathyroid from adjacent structures. It is important to recognize that 4DCT provides valuable information however results in much higher radiation dose to the thyroid gland than the other available examinations, and therefore the optimal number of phases is an area of controversy. Single-photon scintigraphy with 99mTc-Sestamibi, or dual tracer 99mTc-pertechnetate and 99mTc-sestamibi with or without SPECT or SPECT/CT is part of the standard of care in many centers with availability and expertise in nuclear medicine. This molecular imaging approach detects cellular physiology such as mitochondria content found in parathyroid adenomas. Combining structural imaging such as CT or MRI with molecular imaging in a hybrid approach allows the ability to obtain robust structural and functional information in one examination. Hybrid PET/CT is widely available and provides improved imaging and quantification over SPECT or SPECT/CT. Emerging PET imaging techniques, such as 18F-Fluorocholine, have the exciting potential to reinvent parathyroid imaging. PET/MRI may be particularly well suited to parathyroid imaging, where available, because of the ability to perform dynamic contrast-enhanced imaging and co-registered 18F-Fluorocholine PET imaging simultaneously with low radiation dose to the thyroid. A targeted agent specific for a parathyroid tissue biomarker remains to be identified.

The effects of pharmacological interventions, exercise, and dietary supplements on extra-cardiac radioactivity in myocardial perfusion single-photon emission computed tomography imaging

Myocardial perfusion imaging (MPI) as an imaging modality plays a key role in the monitoring of patients with cardiovascular disease. MPI enables the assessment of cardiovascular disease, the effectiveness of therapy, and viable myocardial tissue. However, MPI suffers from some downfalls and limitations, which can influence its clinical applications. These limitations can arise from the patient's condition, equipment, or the actions of the technologist. In this review, we mainly focused on the different effective parameters on radioactivity uptake of organs including liver, intestines, stomach, and gall bladder and how they affect the quality of the acquired images in nuclear medicine. More importantly, we cover how different suggested medicines, foods and exercise alleviative this problem.

Analytically based photon scatter modeling for a multipinhole cardiac SPECT camera

PURPOSE

Dedicated cardiac SPECT scanners have improved performance over standard gamma cameras allowing reductions in acquisition times and/or injected activity. One approach to improving performance has been to use pinhole collimators, but this can cause position-dependent variations in attenuation, sensitivity, and spatial resolution. CT attenuation correction (AC) and an accurate system model can compensate for many of these effects; however, scatter correction (SC) remains an outstanding issue. In addition, in cameras using cadmium-zinc-telluride-based detectors, a large portion of unscattered photons is detected with reduced energy (low-energy tail). Consequently, application of energy-based SC approaches in these cameras leads to a higher increase in noise than with standard cameras due to the subtraction of true counts detected in the low-energy tail. Model-based approaches with parallel-hole collimator systems accurately calculate scatter based on the physics of photon interactions in the patient and camera and generate lower-noise estimates of scatter than energy-based SC. In this study, the accuracy of a model-based SC method was assessed using physical phantom studies on the GE-Discovery NM530c and its performance was compared to a dual energy window (DEW)-SC method.

METHODS

The analytical photon distribution (APD) method was used to calculate the distribution of probabilities that emitted photons will scatter in the surrounding scattering medium and be subsequently detected. APD scatter calculations for ^99mTc-SPECT (140 ± 14 keV) were validated with point-source measurements and 15 anthropomorphic cardiac-torso phantom experiments and varying levels of extra-cardiac activity causing scatter inside the heart. The activity inserted into the myocardial compartment of the phantom was first measured using a dose calibrator. CT images were acquired on an Infinia Hawkeye (GE Healthcare) SPECT/CT and coregistered with emission data for AC. For comparison, DEW scatter projections (120 ± 6 keV ) were also extracted from the acquired list-mode SPECT data. Either APD or DEW scatter projections were subtracted from corresponding 140 keV measured projections and then reconstructed with AC (APD-SC and DEW-SC). Quantitative accuracy of the activity measured in the heart for the APD-SC and DEW-SC images was assessed against dose calibrator measurements. The difference between modeled and acquired projections was measured as the root-mean-squared-error (RMSE). APD-modeled projections for a clinical cardiac study were also evaluated.

RESULTS

APD-modeled projections showed good agreement with SPECT measurements and had reduced noise compared to DEW scatter estimates. APD-SC reduced mean error in activity measurement compared to DEW-SC in images and the reduction was statistically significant where the scatter fraction (SF) was large (mean SF = 28.5%, T-test p = 0.007). APD-SC reduced measurement uncertainties as well; however, the difference was not found to be statistically significant (F-test p > 0.5). RMSE comparisons showed that elevated levels of scatter did not significantly contribute to a change in RMSE (p > 0.2).

CONCLUSIONS

Model-based APD scatter estimation is feasible for dedicated cardiac SPECT scanners with pinhole collimators. APD-SC images performed better than DEW-SC images and improved the accuracy of activity measurement in high-scatter scenarios.

A gamma-distribution convolution model of 99mTc-MIBI thyroid time-activity curves

BACKGROUND

The convolution approach to thyroid time-activity curve (TAC) data fitting with a gamma distribution convolution (GDC) TAC model following bolus intravenous injection is presented and applied to 99mTc-MIBI data. The GDC model is a convolution of two gamma distribution functions that simultaneously models the distribution and washout kinetics of the radiotracer. The GDC model was fitted to thyroid region of interest (ROI) TAC data from 1 min per frame 99mTc-MIBI image series for 90 min; GDC models were generated for three patients having left and right thyroid lobe and total thyroid ROIs, and were contrasted with washout-only models, i.e., less complete models. GDC model accuracy was tested using 10 Monte Carlo simulations for each clinical ROI.

RESULTS

The nine clinical GDC models, obtained from least counting error of counting, exhibited corrected (for 6 parameters) fit errors ranging from 0.998% to 1.82%. The range of all thyroid mean residence times (MRTs) was 212 to 699 min, which from noise injected simulations of each case had an average coefficient of variation of 0.7% and a not statistically significant accuracy error of 0.5% (p = 0.5, 2-sample paired t test). The slowest MRT value (699 min) was from a single thyroid lobe with a tissue diagnosed parathyroid adenoma also seen on scanning as retained marker. The two total thyroid ROIs without substantial pathology had MRT values of 278 and 350 min overlapping a published 99mTc-MIBI thyroid MRT value. One combined value and four unrelated washout-only models were tested and exhibited R-squared values for MRT with the GDC, i.e., a more complete concentration model, ranging from 0.0183 to 0.9395.

CONCLUSIONS

The GDC models had a small enough TAC noise-image misregistration (0.8%) that they have a plausible use as simulations of thyroid activity for querying performance of other models such as washout models, for altered ROI size, noise, administered dose, and image framing rates. Indeed, of the four washout-only models tested, no single model approached the apparent accuracy of the GDC model using only 90 min of data. Ninety minutes is a long gamma-camera acquisition time for a patient, but a short a time for most kinetic models. Consequently, the results should be regarded as preliminary.

Diagnostic Performances of 99mTc-Methoxy Isobutyl Isonitrile Scan in Predicting the Malignancy of Lung Lesions: A Meta-Analysis

We performed a meta-analysis to evaluate the value of technetium-99m methoxy isobutyl isonitrile (Tc-MIBI) single photon emission computed tomography (SPECT) in differentiating malignant from benign lung lesions.The PubMed and Embase databases were comprehensively searched for relevant articles that evaluated lung lesions suspicious for malignancy. Two reviewers independently extracted the data on study characteristics and examination results, and assessed the quality of each selected study. The data extracted from the eligible studies were assessed by heterogeneity and threshold effect tests. Pooled sensitivity, specificity, diagnostic odds ratio (DOR), and areas under the summary receiver-operating characteristic curves (SROC) were also calculated.Fourteen studies were included in this meta-analysis. The pooled sensitivity, specificity, positive and negative likelihood ratio, and DOR of Tc-MIBI scan in detecting malignant lung lesions were 0.84 (95% confidence interval [CI]: 0.81, 0.87), 0.83 (95% CI: 0.77, 0.88), 4.22 (95% CI: 2.53, 7.04), 0.20 (95% CI: 0.12, 0.31), and 25.71 (95% CI: 10.67, 61.96), respectively. The area under the SROC was 0.9062. Meta-regression analysis showed that the accuracy estimates were significantly influenced by ethnic groups (P < 0.01), but not by image analysis methods, mean lesion size, or year of publication. Deek funnel plot asymmetry test for the overall analysis did not raise suspicion of publication bias (P = 0.50).Our results indicated that Tc-MIBI scan is a promising diagnostic modality in predicting the malignancy of lung lesions.

The Effect of Milk, Water and Lemon Juice on Various Subdiaphragmatic Activity-Related Artifacts in Myocardial Perfusion Imaging

Background:

Subdiaphragmatic activity can produce subdiaphragmatic-related artifacts, which can degrade the quality of myocardial perfusion imaging (MPI).

Objectives:

We examined the impact of drinking milk, water, and lemon juice on different subdiaphragmatic-related artifacts by using ^99mTc-sestamibi myocardial single-photon emission computed tomography (SPECT) in order to determine a feasible method for improving the image quality.

Patients and Methods:

A total of 179 patients (age 58 ± 9.6 years) were enrolled in this study. The patients were randomly divided into five groups. Ten minutes after injection of 740 MBq 99mTc-sestamibi in both pharmacologic stress and rest phases, the individuals in group 1 were given water and milk (125 mL of each); those in group 2 were given lemon juice (250 mL); group 3 was given milk (250 mL); and group 4 was given water (250 mL), whereas no intervention was performed in group 5. The study was double-blind for both subjects and data collectors. MPI was performed for all patients and image quality was controlled by 2 experienced nuclear physicians. Interfering activity was determined visually on reconstructed images and categorized as extracardiac normalization artifact, overlapping of activity, scattering of activity, and ramp filter artifact.

Results:

There were significant differences in terms of interfering activity among the five groups; group 3 (milk) had significantly lower interfering activity than other groups had, as defined by overlapping of activity (on both stress and rest images), ramp filter artifact (stress images), and scatter artifact (rest images) (P < 0.05). Furthermore, there was a significant difference in the incidence of good-quality images, with no interfering activity in group 3 in the resting state compared with the other groups in the study (P < 0.05).

Conclusions:

Drinking 250 mL of milk in either the stress phase or the rest phase of imaging diminishes interfering subdiaphragmatic-related artifacts, particularly overlapping of activity in MPI SPECT, resulting in better-quality images.

Effect of menstrual cycle phase on background parenchymal uptake at molecular breast imaging

RATIONALE AND OBJECTIVES

The level of Tc-99m sestamibi uptake within normal fibroglandular tissue on molecular breast imaging (MBI), termed background parenchymal uptake (BPU), has been anecdotally observed to fluctuate with menstrual cycle. Our objective was to assess the impact of menstrual cycle phase on BPU appearance.

MATERIALS AND METHODS

Premenopausal volunteers who reported regular menstrual cycles and no exogenous hormone use were recruited to undergo serial MBI examinations during the follicular and luteal phase. A study radiologist, blinded to cycle phase, categorized BPU as photopenic, minimal mild, moderate, or marked. Change in BPU with cycle phase was determined, as well as correlations of BPU with mammographic density and hormone levels.

RESULTS

In 42 analyzable participants, high BPU (moderate or marked) was observed more often in luteal phase compared to follicular (P = .016). BPU did not change with phase in 30 of 42 participants (71%) and increased in the luteal phase compared to follicular in 12 (29%). High BPU was more frequent in dense breasts compared to nondense breasts at both the luteal (58% [15 of 26] vs. 13% [2 of 16], P = .004) and follicular phases (35% [9 of 26] vs. 6% [1 of 16], P = .061). Spearman correlation coefficients did not show any correlation of BPU with hormone levels measured at either cycle phase and suggested a weak correlation between change in BPU and changes in estrone and estradiol between phases.

CONCLUSIONS

We observed variable effects of menstrual cycle on BPU among our cohort of premenopausal women; however, when high BPU was observed, it was most frequently seen during the luteal phase compared to follicular phase and in women with dense breasts compared to nondense breasts.

Optimization of a protocol for myocardial perfusion scintigraphy by using an anthropomorphic phantom

Objective

To develop a study aiming at optimizing myocardial perfusion imaging.

Materials and Methods

Imaging of an anthropomorphic thorax phantom with a GE SPECT Ventri gamma camera, with varied activities and acquisition times, in order to evaluate the influence of these parameters on the quality of the reconstructed medical images. The ^99mTc-sestamibi radiotracer was utilized, and then the images were clinically evaluated on the basis of data such as summed stress score, and on the technical image quality and perfusion. The software ImageJ was utilized in the data quantification.

Results

The results demonstrated that for the standard acquisition time utilized in the procedure (15 seconds per angle), the injected activity could be reduced by 33.34%. Additionally, even if the standard scan time is reduced by 53.34% (7 seconds per angle), the standard injected activity could still be reduced by 16.67%, without impairing the image quality and the diagnostic reliability.

Conclusion

The described method and respective results provide a basis for the development of a clinical trial of patients in an optimized protocol.

Detection of post-exercise stunning by early gated SPECT myocardial perfusion imaging: results from the IAEA multi-center study

BACKGROUND

Transient post-ischemic LV dysfunction due to myocardial stunning in patients with coronary artery disease can be missed by conventional gated SPECT (GSPECT) acquisitions. The aim of this IAEA-sponsored multi-center study was to determine whether early post-exercise imaging is more likely to detect stunning than conventional without adversely affecting image quality or perfusion information.

METHODS AND RESULTS

Patients undergoing exercise/rest GSPECT were enrolled in this international multicenter study. Post-exercise studies were acquired at 15 ± 5 minutes after radiotracer injection (Stress-1) and repeated at 60 ± 15 minutes (Stress-2). Rest studies (R) were acquired at 60 minutes post injection. A core laboratory quantitatively assessed perfusion pattern and LV blinded to the acquisition time. Ischemia was defined as summed stress score (SDS) ≥4, and stunning was defined as the difference between rest and post-stress LVEF (Δ-LVEF). In the 229 patients enrolled into the study, both image quality and perfusion information were similar between Stress-1 and Stress-2. Post-stress LVEF was associated with both ischemia and time of acquisition, with a significant correlation between SDS and Δ-LVEF, which was stronger at Stress-1 than Stress-2 in the ischemic compared to the non-ischemic population (r = 0.23 vs 0.08, P = 0.10).

CONCLUSIONS

Early post-exercise imaging is feasible, and can potentially improve the detection of post-ischemic stunning without compromising image quality and perfusion data.

Cell injury after ischemia and reperfusion in the porcine kidney evaluated by radiolabelled microspheres, sestamibi, and lactadherin

Background

The purpose of the present study was to quantify renal cell injury after ischemia and reperfusion in a pig model using ^99mTc-lactadherin as a marker of apoptosis and ^99mTc-sestamibi as a marker of mitochondrial dysfunction.

Methods

Thirty-four pigs were randomized into unilateral renal warm ischemia of 120 (WI₁₂₀) or 240 min (WI₂₄₀). The glomerular filtration rate (GFR) was calculated by renal clearance of ⁵¹Cr-ethylenediaminetetraacetic acid, and apoptosis was quantified by immunohistochemical detection of caspase-3. After 240 min of reperfusion, intravenous ^99mTc-lactadherin or ^99mTc-sestamibi was injected simultaneously with ¹⁵³Gd microspheres into the aorta. Ex-vivo static planar images of the kidneys were acquired for determination of the differential renal function of tracer distribution using a gamma camera.

Results

In WI₁₂₀, there was no significant difference in the uptake of microspheres in the ischemic and contralateral normal kidney indicating adequate perfusion (uptake in ischemic kidney relative to the sum of uptake in both kidneys; 46% ± 12% and 51% ± 5%). In WI₂₄₀, the uptake of microspheres was severely reduced in both groups (17% ± 11% and 27% ± 17%). GFR was severely reduced in the post ischemic kidney in both groups.

In both groups, the uptake of lactadherin was reduced (41% ± 8%, 17% ± 13%) but not different from the uptake of ¹⁵³Gd microspheres. Caspase-3-positive cell profiles were increased in the post-ischemic kidneys (p < 0.001) and increased as the length of ischemia increased (p = 0.003). In both WI₁₂₀ and WI₂₄₀, the amount of ^99mTc-sestamibi in the ischemic kidney was significantly lower than the amount of ¹⁵³Gd microspheres (40 ± 5 versus 51 ± 5 and 20 ± 11 versus 27 ± 17; p < 0.05).

Conclusions

In an established pig model with unilateral renal warm ischemia, we found significantly reduced ^99mTc-sestamibi uptake relative to perfusion in the kidneys exposed to ischemia indicating a potential ability to detect renal ischemic and reperfusion injuries. However, apoptosis was not detected using ^99mTc-lactadherin in the post-ischemic kidneys despite increased number of caspase-3-positive cell profiles.

Trial registration

This study is approved by the Danish Inspectorate of Animal Experiments (2010/561-1837).

On the structural modification of 2-nitroimidazole-(99m)Tc(CO)(3) complex, a hypoxia marker, for improving in vivo pharmacokinetics

INTRODUCTION

A 2-nitroimidazole-(99m)Tc(CO)(3) complex reported earlier showed promise with respect to its uptake and retention in hypoxic tumor. However, significant uptake and slow clearance from liver imposed severe limitations towards advocating its possible practical utility. In an attempt to improving its liver clearance, an ether linkage, which is known to help in liver clearance, was introduced in the molecule.

METHODS

The 2-nitroimidazole iminodiacetic acid (IDA) derivative containing an ether linkage was synthesized in a five step procedure from 2-nitroimidazole. This derivative was radiolabeled using [(99m)Tc(CO)(3)(H(2)O)(3)](+) precursor complex. The corresponding Re(CO)(3) analogue was also synthesized in the macroscopic level for structural characterization. The (99m)Tc(CO)(3) complex was evaluated in an animal model bearing fibrosarcoma tumor.

RESULTS

The in vivo evaluation of the complex indicated that, as envisaged, introduction of the ether linkage has improved clearance from the liver. The complex also showed higher retention in tumor compared to the 2-nitroimidazole-IDA-(99m)Tc(CO)(3) complex reported earlier. Though the tumor to muscle ratio improved with time, the tumor to blood ratio did not show any significant improvement. Despite improved liver clearance, there was significant liver activity present even at 3h p.i. attributable to gradual accumulation of activity cleared from muscle and blood.

CONCLUSIONS

Though the introduction of ether linkage improved liver clearance of the modified 2-nitroimidazole complex, it was found that a single ether linkage was not sufficient to achieve the desirable level of clearance. Probably, a linker with multiple ether groups, such as a di- or tri-ethylene glycol spacer, may be a possible solution to this issue.

Characterizing the contribution of cardiac and hepatic uptake in dedicated breast SPECT using tilted trajectories

A small field of view, high resolution gamma camera has been integrated into a dedicated breast, single photon emission computed tomography (SPECT) device. The detector can be flexibly positioned relative to the breast and image beyond the chest wall, allowing the system to capture direct views of the heart and liver. The incomplete sampling of these organs creates artifacts in reconstructed images, complicating lesion detection. To understand the limits imposed on a 3D acquisition trajectory, sequential tilted trajectories at increasing polar tilt are utilized to collect data of anthropomorphic phantoms filled with aqueous (99m)Tc in a clinically realistic concentration ratio. The counts collected per projection between different scans and the SNR, contrast and resolution (FWHM) of two hot lesions were compared. As expected, the counts per projection increased when the camera had direct views of the heart and liver, but remained relatively constant at other angles. The SNR, contrast and FWHM were more affected by the insufficient sampling of the data by the large polar angles than by the cardiac and hepatic activity. An upper bound on polar tilt for each azimuthal position reduces the artifacts in the reconstructed images. Such trajectories were implemented to show artifact-free reconstructed images.

Influence of the different biokinetics of sestamibi and tetrofosmin on the interpretation of myocardial perfusion imaging in daily practice

AIM

Digestive activity can interfere with the interpretation of myocardial perfusion single photon emission computed tomography using sestamibi or tetrofosmin. Compared with sestamibi, the liver clearance of tetrofosmin is more rapid, but its absolute cardiac uptake is lower. In this study, the activity of sestamibi and tetrofosmin was quantified after exercise or pharmacological stress and at rest to objectify the biokinetic differences and to evaluate whether there is a correlation between quantitative measurements and the visual assessment of image quality.

METHODS

Left ventricular activity and five ratios (R1-R5) of cardiac to adjacent extra-cardiac activity were quantified in 204 sestamibi (68 exercise stress/56 pharmacological stress/80 rest) and 221 tetrofosmin (67 exercise stress/59 pharmacological stress/95 rest) studies. Image quality was assessed by a three-point score (1, good; 2, moderate; 3, poor) and correlated with the heart to left supra-diaphragmatic region (R1) and heart to right supra-diaphragmatic region (R2) ratios.

RESULTS

The mean left ventricular activity was higher for sestamibi, especially at rest (sestamibi, 0.21+/-0.05 counts/pixel/injected MBq; tetrofosmin, 0.16+/-0.042 counts/pixel/injected MBq; P<0.001). By contrast, most ratios were higher with tetrofosmin, particularly for the exercise stress and rest studies. Using the three-point quality scoring, more sestamibi than tetrofosmin studies were scored as 3 (12.2% versus 6.3%), also particularly for the exercise stress and rest studies. A highly significant relationship was found between decreasing R1 and R2 and an increasing quality score, regardless of the radiopharmaceutical used (P values between 0.02 and <0.001).

CONCLUSIONS

Despite a lower cardiac uptake, the more rapid liver clearance of tetrofosmin than sestamibi significantly improves the ratios of cardiac to digestive activity, especially after exercise or at rest. These quantitative differences in biokinetics result in less poor scans with tetrofosmin in daily practice.

Relationship of Hepatic Functional Imaging to Irinotecan Pharmacokinetics and Genetic Parameters of Drug Elimination

Purpose

The marked variability of irinotecan (Ir) clearance warrants individualized dosing based on hepatic drug handling. The aims of this trial were to identify parameters from functional hepatic nuclear imaging (HNI) that correlate with (1) Ir pharmacology, and (2) single-nucleotide polymorphisms (SNPs) for the ABCB1 (P-glycoprotein) and UGT-1A1 genes, known to influence Ir handling.

Methods

Patients underwent genotyping for ABCB1 SNPs and UTUGT-1A1*28 carriage and HNI with 99mTc-DIDA (acetanilidoiminodiacetic acid)/ 99mTc-DISIDA (disofenin) and MIBI (99mTc-sestamibi) scans, probes for biliary transport proteins ABCC1 and -2, and ABCB1 function. HNI data were analyzed by noncompartmental and deconvolutional analysis to provide hepatic extraction and biliary excretion parameters. Patients received Ir, fluorouracil, and folinic acid using a weekly ×2, every-3-weeks schedule. Plasma was taken for Ir and SN-38 analysis on day 1, cycle 1.

Results

Of the 21 patients accrued, Ir pharmacokinetics data were obtained from 16 patients. 99mTc-DIDA/DISIDA percent retention at 1 hour (1-hour RET) correlated to baseline serum bilirubin (P = .008). Both 99mTc-DIDA/DISIDA and MIBI 1-hour RET correlated with SN-38 area under the curve (AUC; P < .01). On multiple regression analysis, SN-38 AUC = −215 + 18.68 × bilirubin + 4.27 × MIBI 1-hour RET (P = .009, R2 = 44.2%). HNI parameters did not correlate with Ir toxicity or UGT1A1*28 carriage. MIBI excretion was prolonged in patients with the ABCB1 exon 26 TT variant allele relative to wild-type (P = .015).

Conclusion

Functional imaging of hepatic uptake and excretory pathways may have potential to predict Ir pharmacokinetics. Evaluation of a larger cohort as well as polymorphisms in other biliary transporters and UGT1A1 alleles is warranted.

Comparison of ST-segment deviation to scintigraphically quantified myocardial ischemia during acute coronary occlusion induced by percutaneous transluminal coronary angioplasty

This study compared ST-segment changes during acute coronary artery occlusion with measurements of ischemia by myocardial scintigraphy. Forty patients who were referred for elective prolonged percutaneous transluminal coronary angioplasty underwent 12-lead electrocardiographic recording before the procedure (baseline) and continuously during the entire balloon inflation (occlusion). For each patient, the summed ST-segment deviation was calculated as the maximal absolute difference, elevation or depression, between baseline and occlusion recordings in all 12 leads. Each patient underwent 2 myocardial scintigraphies, 1 with technetium-99m sestamibi injected during the balloon inflation and 1 on the following day as a control study. Ischemia that was induced by balloon occlusion was quantified in terms of extent and severity. Results for the entire study group showed that summed ST deviation correlated with extent (r = 0.59, p < 0.0001) and severity (r = 0.61, p < 0.0001) of ischemia. The location of maximal ST deviation differed for the 3 arteries. For occlusion of the left anterior descending artery, maximal ST deviation was elevated in lead V3. For occlusion of the left circumflex artery, maximal ST deviation was depressed in lead V2. Occlusion of the right coronary artery caused ST elevation in lead III and ST depression in lead V2. In conclusion, this study demonstrated a significant correlation between summed ST deviation and myocardial ischemia during coronary occlusion that is induced by percutaneous transluminal coronary angioplasty.

Increasing the radiochemical purity of 99mTc sestamibi commercial preparations results in improved sensitivity of dual-phase planar parathyroid scintigraphy

BACKGROUND

Poor results for dual-phase parathyroid scintigraphy have recently prompted increased use of dual-tracer imaging. We noticed that seminal studies used higher radiochemical purity than provided by current commercial preparations meeting US Pharmacopea (USP) specifications (90% of technetium bound to sestamibi). We surmised that the presence of unbound Tc (non-MIBI tracer) might hamper dual-phase detection that is dependent on rapid wash-out of technetium from thyroid tissue.

PURPOSE

To test the hypothesis that reducing non-MIBI tracer will enhance thyroid wash-out and improve sensitivity of dual-phase imaging.

METHODS

Starting in April 2003 we decreased the technetium to sestamibi ratio. This resulted in a significant decrease of non-MIBI tracer from 8.1+/-2.2% (SD) (group 1, n = 42) to 3.5+/-1.1% (group 2, n = 47) (P < 0.05 t-test). We performed a retrospective review of 89 patients with primary hyperparathyroidism who underwent imaging and subsequent surgery. The pathological findings served as the 'gold standard'.

RESULTS

Scanning detected 21/39 diseased glands (sensitivity=54%) in group 1 patients. In group 2 imaging detected 38/45 diseased glands (sensitivity = 84%). An improvement in sensitivity (P < 0.01) was achieved by modifying the radiopharmaceutical preparation.

CONCLUSIONS

Elevated levels of non-MIBI tracer in Tc-MIBI commercial preparations result in persistent thyroid background activity that may interfere with detection of parathyroid pathology. Achieving a higher degree of radiochemical purity (at least 95% bound, 5% impurities) than required by USP may be needed for optimal results. The large variation in sensitivity reported in the literature may be related in part to non-uniform radiopharmaceutical preparation.

EVALUATION OF LYMPHOMA IN A CAT USING 99mTc-SESTAMIBI

This report describes the evaluation of cutaneous lymphoma in a cat using 99mTc-sestamibi. A mass in the left pes with extension to the left popliteal lymph node was diagnosed as B-cell lymphoma. Thoracic and abdominal radiography and abdominal ultrasound were unremarkable. Scintigraphy using 99mTc-sestamibi confirmed the lesion was confined to the left hind leg, and the leg was amputated. The cat made a full recovery.

99mTc-sestamibi thyroid uptake in euthyroid individuals and in patients with autoimmune thyroid disease

PURPOSE

We investigated the biokinetics of (99m)Tc-sestamibi in the thyroid of euthyroid volunteers (EVs) and in patients with autoimmune thyroid diseases and determined the best time interval between (99m)Tc-sestamibi injection and calculation of uptake.

METHODS

Forty EVs, 30 patients with Graves' disease (GD), 15 patients with atrophic Hashimoto's thyroiditis (AHT) and 15 patients with hypertrophic Hashimoto's thyroiditis (HHT) underwent (99m)Tc-sestamibi thyroid scintigraphy. Dynamic images were acquired for 20 min, and static images were obtained 20 min, 60 min and 120 min post injection. Five-, 20-, 60- and 120-min uptake, time to maximal uptake (T(max)) and T(1/2) of tracer clearance were calculated. Thyroid hormones and antibodies were measured. (99m)Tc-pertechnetate uptake was investigated in GD patients.

RESULTS

T(max) was approximately 5 min in all four groups. The mean T(1/2) value for EVs was similar to the GD value and lower than the HHT and AHT values. The mean (+/-SD) 5-min uptake was 0.13% (+/-0.05%) for EVs. The 5-min uptake in GD was higher than that in EVs(P<0.001) and correlated with free thyroxine (r=0.54) and with (99m)Tc-pertechnetate uptake (r=0.68). Uptake in HHT was higher than that in AHT (P=0.0003) and EVs (P=0.002). Uptake in AHT was lower than uptake in EVs (P=0.0001).

CONCLUSION

Five minutes is the optimal time interval between (99m)Tc-sestamibi injection and calculation of thyroid uptake. Five-minute uptake differentiates euthyroid individuals from GD patients. There is a high correlation between (99m)Tc-sestamibi and (99m)Tc-pertechnetate uptake in GD. The reduced (99m)Tc-sestamibi uptake in AHT patients is probably due to glandular destruction and fibrosis. Inflammatory infiltrate and high mitochondrial density in thyrocytes possibly explain the increased uptake in GD and HHT.

Tc-99m sestamibi uptake in the chest mimicking a malignant lesion of the breast

The use of nuclear medicine imaging of the breast has resulted in the improved diagnosis of breast cancer (Radiology 196 (1995) 421; J. Nucl. Med. 36 (1995) 1758). It's use is becoming more widespread, particularly as breast optimized scintigraphy with a high-resolution, breast-specific gamma camera has been developed (J. Nucl. Med. 43 (2002) 909; J. Nucl. Med. 45 (2004) 553). With the increasing use of breast-optimized scintigraphy, pitfalls in the interpretation of breast-optimized scintigraphy are being recognized. This report describes a previously unrecognized cause for a false positive interpretation of scintimammography due to tumor uptake of the radiotracer in the chest as a result of physiologic activity in the auricular aspect of the right atrium.

The effect of imaging time, radiopharmaceutical, full fat milk and water on interfering extra-cardiac activity in myocardial perfusion single photon emission computed tomography

BACKGROUND AND AIM

Extra-cardiac activity can interfere with observer interpretation of myocardial perfusion single photon emission computed tomography (SPECT) images. Fatty meals and drinks to reduce interference have been tested; however, a simple study of delayed imaging with (99m)Tc-tetrofosmin and (99m)Tc-sestamibi has not been specifically addressed. The aim was to quantify the effects of imaging time, radiopharmaceutical and oral administration of full fat milk and water on interfering activity.

METHODS

Myocardial perfusion SPECT images were acquired using either tetrofosmin or sestamibi. Patients were imaged at 0.5, 1 or 2 h post-injection (tetrofosmin, 59; sestamibi, 72). Additional groups of patients were imaged either with or without milk (tetrofosmin, 54; sestamibi, 45) and with milk and water (sestamibi, 30). A myocardial region was drawn on the anterior projection and a thin adjacent extra-cardiac region was generated automatically. The count density ratio was calculated and validated with a trial of five observers. A decreasing ratio correlated significantly with observer rank of increasing interference with SPECT image interpretation (r=0.95, P=0.001).

RESULTS

The ratio improved significantly as the imaging time increased for both tetrofosmin and sestamibi groups (P<0.05). The groups given milk or milk plus water showed no significant improvement against control groups (P > or = 0.2). There was no significant difference between tetrofosmin and sestamibi at any time point (P > or = 0.4).

CONCLUSIONS

Image interpretation may be improved by delayed imaging for tetrofosmin and sestamibi. However, in contrast with common practice, the administration of milk or water appears to be of no clinical value compared with delayed imaging, and there is no significant difference between interfering activity from tetrofosmin and sestamibi.

Arterial concentration of 99mTc-sestamibi at rest, during peak exercise and after dipyridamole infusion

Tracers for myocardial perfusion imaging during stress should not only have high cardiac uptake but they should also have a fast blood clearance to prevent myocardial tracer uptake after the ischaemic stimulus. The present study characterize the early phase of the arterial (99m)Tc-sestamibi (MIBI) time-activity curve after venous bolus injection at rest, during peak exercise and after dipyridamole infusion. We included 11 patients undergoing angioplasty for one-vessel disease (rest study) and 20 patients evaluated for the detection of haemodynamic significant coronary stenoses by (99m)Tc-sestamibi single photon emission computed tomography (SPECT) using either bicycle exercise testing (10 patients) or standard dipyridamole testing (10 patients). Arterial blood samples of 1 ml were taken from the left femoral artery (rest study) or the right radial artery (exercise and dipyridamole studies) every 5 s during the first 5 min postinjection. In the exercise and the dipyridamole studies blood sampling were extended to include blood samples every 5 min 5-30 min postinjection. Peak MIBI concentration was lower and decrease in concentration slower after tracer injection during exercise than during dipyridamole stress testing. This may cause an underestimation of perfusion defects during exercise because of MIBI uptake after the ischaemic stimulus. The implications of the study not only refer to the choice of stress modality when using MIBI. This study also underlines the importance of considering early blood clearance in addition to regional myocardial tracerkinetic aspects such as myocardial extraction fraction when new tracers are introduced.

Potential of a Compton camera for high performance scintimammography

In this paper, we present a novel approach to scintimammography that is based on the Compton camera principle. We analyse the performance of our scheme using Monte Carlo simulations. In particular, we evaluate the detection efficiency, spatial resolution and lesion visibility of the system at several gamma photon energies. The simulation results show that the proposed technique achieves an absolute detection efficiency of 0.03 and a full width at half maximum resolution of 3.8 mm at 141 keV photon energy for point sources 2.5 cm deep in a 5 cm thick breast phantom using 5 mm thick silicon detectors. Furthermore, our approach shows good performance in lesion detection, especially at high gamma photon energies, where mechanically collimated systems perform poorly due to severe septal penetration. With total collected counts of 1.35 million, equivalent to a 30 s acquisition time for an activity concentration level of 3.7 kBq ml(-1) (100 nCi cm(-3)) in normal breast tissue, and a tumour-to-background ratio of 8:1, our system can clearly reveal an 8 mm diameter tumour that is located 2.5 cm deep in a 500 ml breast phantom. We also present a simulation-based quantitative performance comparison between the proposed scintimammographic system and the compact collimated scintimammographic system in the task of lesion detection under a clinical imaging situation using a non-prewhitening matched filter observer model. Our comparison demonstrates that for the same imaging time, the two systems have a comparable performance in detecting an 8 mm tumour at 141 keV, with the proposed system performing marginally better. However, the proposed scintimammographic system clearly outperforms the compact collimated counterpart in the detection of a 5 mm tumour. We also investigate the contribution of scatter and direct radiation from adjacent organs. We find that the background contribution of liver to the right breast is 30% at 141 keV, which can be reduced to 4.8% with shielding.

Utility of technetium-99m methoxyisobutyl isonitrile uptake analysis for prediction of the response to chemotherapy in advanced and relapsed breast cancer

BACKGROUND

Technetium-99m methoxyisobutyl isonitrile (Tc-SESTAMIBI) is a substrate of P-glycoprotein and multidrug-resistance associated protein in drug-resistant cells. To assess the clinical effectiveness of Tc-SESTAMIBI for predicting the chemotherapy response to treatment with anthracyclines and vinca alkaloids, we retrospectively evaluated the relationship between the accumulation of Tc-SESTAMIBI and the tumor response.

METHODS

Thirteen patients, including 12 advanced cases and 1 relapsed case, were investigated, all of whom had been treated with anthracyclines or a vinca alkaloid regimen. The accumulation of Tc-SESTAMIBI was compared at 10 min and 2 h after Tc-SESTAMIBI administration. The relationship between the accumulation of Tc-SESTAMIBI and the tumor response following treatment with anthracyclines and vinca alkaloids was assessed.

RESULTS

Eight of 13 patients responded to treatment with anthracyclines and vinca alkaloids, whereas 5 patients did not respond to treatment. At 10 min, 6 (75.0% ) of the 8 responding patients had a high accumulation of Tc-SESTAMIBI, whereas 4 (80.0% ) of the 5 non-responding patients had a low accumulation of Tc-SESTAMIBI. The overall predictive value was 76.9%. The relationship was not statistically significant (Fisher's test). The difference in the decrease of accumulation of Tc-SESTAMIBI between 10 min and 2 h was not associated with tumor response to treatment in 6 of the responding patients with high accumulation. Two false negative cases and one false positive case were observed, suggesting the presence of another factor contributing to drug sensitivity in tumor response, such as apoptosis-related genes.

CONCLUSIONS

Assessment of the initial accumulation of Tc-SESTAMIBI can be a predictive marker of tumor response to treatment with anthracyclines and vinca alkaloids in patients with advanced and relapsed breast cancer. Further studies are required to explore other factors involved in the tumor response to treatment with anthracyclines and vinca alkaloids.

Quantification of myocardial hypoperfusion with 99m Tc-sestamibi in patients undergoing prolonged coronary artery balloon occlusion

Percutaneous transluminal coronary angioplasty provides an excellent opportunity to investigate the location and quantity of hypoperfusion during sudden complete occlusion of one of the major coronary arteries. Thirty-five patients referred for elective percutaneous transluminal coronary angioplasty were injected intravenously with 99mTc-sestamibi during balloon inflation. To visualize and quantify the hypoperfused region, a map of perfusion was constructed from that occlusion study and from the control study performed on the following day. Patients were divided into groups according to proximal or distal occlusion within each of the three coronary arteries. The region of myocardium supplied by each coronary artery varied in location and extended outside the typical borders for all arteries, but most prominently for the left circumflex coronary artery. The quantities of hypoperfusion varied within each artery group, but the average hypoperfusion was greater for the left anterior descending coronary artery than for either the right coronary artery or the left circumflex coronary artery. It is concluded that the quantities of hypoperfusion were highly variable within each artery group. Occlusion of the left anterior descending coronary artery was associated with the largest ischaemic region. The area of hypoperfusion extended outside the typical borders, most prominently for the left circumflex coronary artery.

The comparison of dual phase Tc-99m MIBI and tc-99m MDP scintimammography in the evaluation of breast masses: preliminary report

The aim of this prospective study was to determine the diagnostic value of Tc-99m MDP scintimammography (SMG) for the detection of breast cancer in patients with breast masses and to compare the results with Tc-99m MIBI scintimammography. Twenty patients, categorized as suspicious, positive or benign for breast cancer according to the mammographic findings were included in the study. Dual phase Tc-99m MIBI and Tc-99m MDP SMG were performed in the prone lateral position within 5 days of each other. Although early and late Tc-99m MIBI SMG showed equal (90.4%) sensitivity, the specificity of late Tc-99m MIBI (87.5%) was found superior to early (62.5%) imaging. The overall sensitivity and specificity of early Tc-99m MDP SMG were 71.4% and 62.5%, respectively. Although late Tc-99m MDP imaging showed 100% specificity, its sensitivity was only 23.8%. In the patients with palpable masses, both early Tc-99m MDP and Tc-99m MIBI showed equal sensitivity (100%), but the sensitivity of early Tc-99m MIBI (37.5%) was found slightly higher than Tc-99m MDP (25.0%) for nonpalpable breast lesions. The sensitivity of Tc-99m MIBI and Tc-99m MDP SMG in detecting metastatic axillary involvement was 66.6% and 50%, respectively. High sensitivity and specificity together with its low cost, easy availability and the possibility of detecting bone metastases seems to make Tc-99m MDP a contributive agent in the evaluation of breast lesions as an alternative to Tc-99m MIBI.

Accuracy evaluation of fusion of CT, MR, and spect images using commercially available software packages (SRS PLATO and IFS)

PURPOSE

A problem for clinicians is to mentally integrate information from multiple diagnostic sources, such as computed tomography (CT), magnetic resonance (MR), and single photon emission computed tomography (SPECT), whose images give anatomic and metabolic information.

METHODS AND MATERIALS

To combine this different imaging procedure information, and to overlay correspondent slices, we used commercially available software packages (SRS PLATO and IFS). The algorithms utilize a fiducial-based coordinate system (or frame) with 3 N-shaped markers, which allows coordinate transformation of a clinical examination data set (9 spots for each transaxial section) to a stereotactic coordinate system. The N-shaped markers were filled with fluids visible in each modality (gadolinium for MR, calcium chloride for CT, and 99mTc for SPECT). The frame is relocatable, in the different acquisition modalities, by means of a head holder to which a face mask is fixed so as to immobilize the patient. Position errors due to the algorithms were obtained by evaluating the stereotactic coordinates of five sources detectable in each modality.

RESULTS

SPECT and MR position errors due to the algorithms were evaluated with respect to CT: deltax was < or = 0.9 mm for MR and < or = 1.4 mm for SPECT, deltay was < or = 1 mm and < or = 3 mm for MR and SPECT, respectively. Maximal differences in distance between estimated and actual fiducial centers (geometric mismatch) were in the order of the pixel size (0.8 mm for CT, 1.4 mm for MR, and 1.8 mm for SPECT). In an attempt to distinguish necrosis from residual disease, the image fusion protocol was studied in 35 primary or metastatic brain tumor patients.

CONCLUSIONS

The image fusion technique has a good degree of accuracy as well as the potential to improve the specificity of tissue identification and the precision of the subsequent treatment planning.

Tc-99m MIBI thoracic SPECT for the detection of intrathoracic tumor masses

Thirty-one men (age range, 46-76 years; mean age, 64.8 years) with intrathoracic masses suggesting possible malignancy on the basis of chest radiography or CT underwent preoperative Tc-99m MIBI SPECT examinations. Diagnosis was confirmed on pathologic examinations of samples obtained either at thoracotomy, esophagectomy, or by biopsy. Twenty-five patients had primary lung cancer, including squamous cell carcinoma, large cell carcinoma, adenocarcinoma, and small cell carcinoma. Two patients had lymphomas with spread to the mediastinum, and three patients had extrathoracic primary cancers (one squamous cell carcinoma of esophagus, one squamous cell carcinoma originating from a head and neck tumor, and one metastatic mediastinal leiomyosarcoma). One patient with a tuberculoma had negative results of the Tc-99m MIBI examination. Tc-99m MIBI had a 86.7% sensitivity rate, a 0% false-positive rate, and a 100% positive predictive value to detect malignant intrathoracic masses. There was a 13% false-negative rate, however, suggesting that MIBI-SPECT may underdiagnose malignant lesions. SPECT findings of these 31 patients can be classified as 1) mass with increased uptake, n = 23; 2) ring-like appearance of increased uptake, n = 3; 3) mass with absent uptake, n = 4; and 4) photon-deficient mass, n = 1. Absent uptake in patients with mass lesions could be explained by necrosis of the lesion (caseation necrosis or massive tumor necrosis with or without bleeding). Most malignant intrathoracic masses are Tc-99m MIBI avid and may be detected with a high degree of sensitivity and with an excellent positive predictive value. A positive MIBI scan may help in the clinical diagnosis of malignancy. The use of Tc-99m MIBI could serve not only as a tumor imaging agent, but also may be used to determine the extent of spread and potentially the chemotherapeutic responsiveness of a tumor.

Influence of background correction in the estimation of myocardial uptake of 99mTc labelled perfusion imaging agents

The effects of different corrections for background activity in the estimation of low organ uptake of radiopharmaceuticals have been examined using myocardial perfusion imaging agents. Estimates of myocardial uptake of 99mTc-labelled MIBI and tetrofosmin were made both at rest and after exercise. Patients were given one or other of the agents (12 MIBI; 17 tetrofosmin) and the measurements at rest and after exercise were made within a week of each other using a planar gamma camera method incorporating an attenuation-corrected, geometric mean technique. Myocardial uptakes were estimated using two different background corrections and also with no background subtraction. Mean values were in the range 1.3 to 3.0% and showed that, for both agents, uptakes estimated with and without background correction could differ by a factor of two. Although the study was not designed to compare myocardial uptakes of the two agents, a background correction which accounted separately for activity in tissue over- and under-lying the heart resulted in similar mean values for tetrofosmin (1.7% both at rest and after exercise) and for MIBI (1.8% rest; 1.9% exercise). For both agents, no significant difference was observed between myocardial uptakes at rest and after exercise measured at about two hours post-injection.

Abnormal uptake of Tc-99m MIBI, a novel myocardial imaging agent, in the lungs of patients with systemic sclerosis

OBJECTIVE

Fibrosing alveolitis is a prominent feature of systemic sclerosis (SSc), and accounts for much of the morbidity and mortality of this disease. Sensitive techniques for the detection and monitoring of fibrosing alveolitis could target patients for early therapeutic intervention. The objective of this small pilot study was to assess the frequency and clinical significance of abnormal lung uptake of Tc-99m MIBI, a novel radionuclide imaging agent that selectively accumulates in cells rich in mitochondria.

METHODS

Sixteen patients with SSc and evidence of pulmonary involvement were studied. The uptake of radionuclide in the lungs, and the ratio of pulmonary to cardiac uptake were evaluated after intravenous injection of Tc-99m MIBI. Results were correlated with clinical and laboratory parameters.

RESULTS

Lung uptake of Tc-99m MIBI was increased in all 16 SSc patients compared to control patients with coronary heart disease but no evidence of pulmonary abnormality. The degree of isotope uptake in the lungs was correlated with the extent of maximal skin induration and with radiologic evidence of interstitial lung disease, but not with other clinical or laboratory parameters of disease activity or extent of pulmonary involvement. The ratio of pulmonary to cardiac uptake of isotope was also increased in patients with SSc compared to controls.

CONCLUSION

Accumulation of Tc-99m MIBI is abnormally elevated in the lungs of SSc patients with pulmonary involvement. Isotope accumulation in the lungs may be related to activation of fibroblasts or endothelial cells. The specificity and sensitivity of Tc-99m MIBI scanning in the detection and monitoring of pulmonary involvement, and its potential role in the management of SSc, deserve further investigation.

Clinical role of technetium-99m sestamibi single-photon emission tomography in evaluating pretreated patients with brain tumours

One of the main problems regarding the follow-up of patients with brain tumours treated with radiotherapy is the distinction between radiation necrosis and tumour relapse. In many cases computed tomography (CT) scan is unable to distinguish between the two. We assessed the usefulness of brain single-photon emission tomography (SPET) with technetium-99m-sestamibi in cases where CT scan was not conclusive. The absence of tracer uptake in normal brain, the sharp uptake in neoplastic tissue, and the favourable physical properties of technetium make the scintigraphic method particularly accurate. We therefore propose the association of CT scan with 99mTc-sestamibi brain SPET in the follow-up of patients in whom a distinction between radiation necrosis and active disease is needed for an adequate therapeutic decision.

Clinical utility of technetium-99m methoxisobutylisonitrile imaging in differentiated thyroid carcinoma: comparison with thallium-201 and iodine-131 Na scintigraphy, and serum thyroglobulin quantitation

Recently, technetium-99m methoxyisobutylisonitrile (99mTc-MIBI) has been used to image thyroid carcinoma. A prospective study was performed to compare the efficacy of 99mTc-MIBI to thallium-201 (201Tl) scintigraphy in patients with differentiated thyroid carcinoma. The clinical utility of all radionuclide imaging modalities, i.e., 99mTc-MIBI, 201Tl, and iodine-131 Na (131I-Na), as well as serum thyroglobulin estimation, was evaluated. Thirty-four post-thyroidectomy patients (age range: 26-76 years) underwent 45 studies. Histopathologies studied included fourteen papillary, eight papillary-follicular, ten follicular, one Hürthle cell, and one medullary carcinoma of the thyroid. Following optimal stimulation of endogenous thyroid stimulating hormone (i.e, TSH 50 mU/ml), the patients underwent 201Tl and 99mTc-MIBI scintigraphy. Concomitant 131I-Na scintigraphy was performed and serum thyroglobulin levels were measured. Sixteen scan sets were performed prior to 131I-Na ablation therapy. Twenty-nine scan sets were performed following 131I-Na ablation therapy. The presence or absence of thyroid cancer was established by clinical, biochemical, radiologic, and/or biopsy findings. There was no significant difference in sensitivity and specificity of 201Tl scintigraphy versus 99mTc-MIBI scintigraphy in pre- and postablation studies. 131I-Na scintigraphy with determination of thyroglobulin level was sufficient in preablation studies. Among postablation patients, the addition of 99mTc-MIBI or 201Tl offered a higher diagnostic yield. Between the 201Tl and 99mTc-MIBI studies, there was a concordance of 69% in preablation and 97% among postablation patients (P=0.027). It is concluded that 99mTc-MIBI is a suitable alternative to 201Tl scintigraphy in thyroid carcinoma, especially following thyroidectomy and 131I-Na therapy. 131I-Na scintigraphy with serum thyroglobulin is adequate in both pre- and postablation patients. Among the post-131I-Na ablation patients, 99mTc-MIBI or 201Tl is extremely valuable for tumor localization, especially when the 131I-Na whole-body scan is negative. The combination of 99mTc-MIBI or 201Tl scintigraphy with 131I-Na and serum thyroglobulin offers the highest diagnostic yield.

The use of technetium-99m methoxyisobutylisonitrile breast scintigraphy to evaluate palpable breast masses

Thirty-eight female patients (age range: 31-79 years) with breast masses underwent technetium-99m methoxyisobutylisonitrile (99mTc-MIBI) breast scintigraphy in order to assess the value of this technique in the detection of breast carcinomas and in their differentiation from benign breast masses. The results showed that 27 of the 32 cases of breast carcinoma were detected by 99mTc-MIBI breast scintigraphy. In contrast, none of the six benign lesions could be detected by this method. The diagnostic sensitivity, specificity and accuracy were 84%, 100% and 87%, respectively, in the differentiation of malignant and benign breast masses. In conclusion, we consider 99mTc-MIBI breast scintigraphy is useful in distinguishing malignancies from benign breast masses.