Cardiac autonomic imaging with SPECT tracers

Radionuclide cardiac imaging has potential to assess underlying molecular, electrophysiologic, and pathophysiologic processes of cardiac disease. An area of current interest is cardiac autonomic innervation imaging with a radiotracer such as ¹²³I-meta-iodobenzylguanidine (¹²³I-mIBG), a norepinephrine analogue. Cardiac ¹²³I-mIBG uptake can be assessed by planar and SPECT techniques, involving determination of global uptake by a heart-to-mediastinal ratio, tracer washout between early and delayed images, and focal defects on tomographic images. Cardiac ¹²³I-mIBG findings have consistently been shown to correlate strongly with heart failure severity, pre-disposition to cardiac arrhythmias, and poor prognosis independent of conventional clinical, laboratory, and image parameters. ¹²³I-mIBG imaging promises to help monitor a patient’s clinical course and response to therapy, showing potential to help select patients for an ICD and other advanced therapies better than current methods. Autonomic imaging also appears to help diagnose ischemic heart disease and identify higher risk, as well as risk-stratify patients with diabetes. Although more investigations in larger populations are needed to strengthen prior findings and influence modifications of clinical guidelines, cardiac ¹²³I-mIBG imaging shows promise as an emerging technique for recognizing and following potentially life-threatening conditions, as well as improving our understanding of the pathophysiology of various diseases.     

Impact of age on myocardial uptake of 123I-mIBG in older adult subjects without coronary heart disease

Background

The purpose of this study was to examine the relationship between myocardial uptake of ¹²³I-mIBG and age in older normal adult subjects.

Methods

94 subjects (age 29-82, mean 58.5) without coronary heart disease were studied. All subjects underwent early and delayed planar and 4-hour SPECT ¹²³I-mIBG imaging. ¹²³I-mIBG uptake was quantified as heart/mediastinum ratio on planar images (H/M _p) and on SPECT images (H/M _s) reconstructed by filtered backprojection, ordered subsets-expectation maximization (OSEM), and OSEM with compensation for collimator septal penetration (DSP). Relationships between age and ¹²³I-mIBG uptake were examined by correlation analysis, t-tests, and analysis of variance.

Results

There was no significant correlation between age and H/M _p, reflecting comparable increases in activity in the two regions of interest with age. Results on SPECT analyses were comparable, with no significant correlation between age and H/M _s. Using DSP, ¹²³I-mIBG H/M _s was significantly higher in subjects ≥70 of age compared with younger subjects.

Conclusions

Both cardiac and background uptake of ¹²³I-mIBG increase with age in older subjects without coronary heart disease, resulting in stability of H/M results (planar and SPECT). This study suggests that prognostic analyses of quantitative ¹²³I-mIBG uptake in patients with heart disease do not require adjustment for patient age.     

Cardiac autonomic neuropathy in patients with diabetes and no symptoms of coronary artery disease: comparison of 123I-metaiodobenzylguanidine myocardial scintigraphy and heart rate variability

Purpose

The purpose of this study was to evaluate the prevalence of cardiac autonomic neuropathy (CAN) in a cohort of patients with type 2 diabetes, truly asymptomatic for coronary artery disease (CAD), using heart rate variability (HRV) and ¹²³I-metaiodobenzylguanidine (¹²³I-mIBG) myocardial scintigraphy.

Methods

The study group comprised 88 patients with type 2 diabetes prospectively recruited from an outpatient diabetes clinic. In all patients myocardial perfusion scintigraphy, CAN by HRV and ¹²³I-mIBG myocardial scintigraphy were performed. Two or more abnormal tests were defined as CAN-positive (ECG-based CAN) and one or fewer as CAN-negative. CAN assessed by ¹²³I-mIBG scintigraphy was defined as abnormal if the heart-to-mediastinum ratio was <1.8, the washout rate was >25%, or the total defect score was >13.

Results

The prevalence of CAN in patients asymptomatic for CAD with type 2 diabetes and normal myocardial perfusion assessed by HRV and ¹²³I-mIBG scintigraphy was respectively, 27% and 58%. Furthermore, in almost half of patients with normal HRV, ¹²³I-mIBG scintigraphy showed CAN.

Conclusion

The current study revealed a high prevalence of CAN in patients with type 2 diabetes. Secondly, disagreement between HRV and ¹²³I-mIBG scintigraphy for the assessment of CAN was observed.     

Characterization of Japanese standards for myocardial sympathetic and metabolic imaging in comparison with perfusion imaging

Objective  The standard patterns of myocardial radiotracer distribution of ¹²³I-metaiodobenzylguanidine (MIBG) and ¹²³I-β-methyl-p-iodophenyl-pentadecanoic acid (BMIPP) should be defined in a Japanese population. The purpose of this study was to present and provide data on the characteristics of MIBG and BMIPP with respect to myocardial single photon emission computed tomography. Methods  The normal database included ¹²³I-MIBG and ¹²³I-BMIPP imaging and a ^99mTc-sestamibi/tetrofosmin myocardial perfusion study. The projection images were transferred by digital imaging and communications in medicine (DICOM) format and reconstructed and analyzed with polar maps. Results  The projection data from multiple centers were successfully transferred to a common format for SPECT reconstruction. When the average values were analyzed using a 17-segment model, MIBG uptake in the inferior and apical wall appeared to be slightly lower than anterior uptake (P < 0.05). The inferior and apical uptake of MIBG has a larger standard deviation (10.7 units in males, 12.6 units in females). BMIPP uptakes in the septal wall have higher than that of ^99mTc-tracer uptake (P < 0.05). Conclusion  Myocardial sympathetic nerve and metabolic scintigraphy data that were specific for the Japanese population were generated and found to be different from that of perfusion tracers. The normal database can serve as a standard for nuclear cardiology work conducted in Japan.     

Agreement and disagreement between contrast-enhanced magnetic resonance imaging and nuclear imaging for assessment of myocardial viability

Purpose  The purpose of this study was to compare contrast-enhanced MRI and nuclear imaging with ^99mTc-tetrofosmin and ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) single photon emission computed tomography (SPECT) for assessment of myocardial viability. Methods  Included in the study were 60 patients with severe ischaemic left ventricular (LV) dysfunction who underwent contrast-enhanced MRI, ^99mTc-tetrofosmin and ¹⁸F-FDG SPECT. Myocardial segments were assigned a wall motion score from 0 (normokinesia) to 4 (dyskinesia) and a scar score from 0 (no scar) to 4 (76–100% transmural extent). Furthermore, ^99mTc-tetrofosmin and ¹⁸F-FDG segmental tracer uptake was categorized from 0 (tracer activity >75%) to 3 (tracer activity <25%). Dysfunctional segments were classified into viability patterns on SPECT: normal perfusion/¹⁸F-FDG uptake, perfusion/¹⁸F-FDG mismatch, and mild or severe perfusion/¹⁸F-FDG match. Results  Minimal scar tissue was observed on contrast-enhanced MRI (scar score 0.4±0.8) in segments with normal perfusion/¹⁸F-FDG uptake, whereas extensive scar tissue (scar score 3.1±1.0) was noted in segments with severe perfusion/¹⁸F-FDG match (p < 0.001). High agreement (91%) for viability assessment between contrast-enhanced MRI and nuclear imaging was observed in segments without scar tissue on contrast-enhanced MRI as well as in segments with transmural scar tissue (83%). Of interest, disagreement was observed in segments with subendocardial scar tissue on contrast-enhanced MRI. Conclusion  Agreement between contrast-enhanced MRI and nuclear imaging for assessment of viability was high in segments without scar tissue and in segments with transmural scar tissue on contrast-enhanced MRI. However, evident disagreement was observed in segments with subendocardial scar tissue on contrast-enhanced MRI, illustrating that the nonenhanced epicardial rim can contain either normal or ischaemically jeopardized myocardium.     

I-123-<Emphasis Type="Italic">m</Emphasis>IBG myocardial imaging for assessment of risk for a major cardiac event in heart failure patients: insights from a retrospective European multicenter study

Purpose Single-center experiences have shown that myocardial meta-iodobenzylguanidine (mIBG) uptake has prognostic value in heart failure (HF) patients. To verify these observations using a rigorous clinical trial methodology, a retrospective review and prospective quantitative reanalysis was performed on a series of cardiac ¹²³I-mIBG scans acquired during a 10-year period at six centers in Europe. Methods ¹²³I-mIBG scans obtained on 290 HF patients [(262 with left ventricular ejection fraction (LVEF) < 50%)] from 1993 to 2002 were reanalyzed using a standardized methodology to determine the heart-to-mediastinum ratio (H/M) on delayed planar images. All image results were verified by three independent reviewers. Major cardiac events [MCEs; cardiac death, cardiac transplant, potentially fatal arrhythmia (including implantable cardioverter-defibrillator discharge)] during 24-month follow-up were confirmed by an adjudication committee. Results MCEs occurred in 67 patients (26%): mean H/M ratio was 1.51 ± 0.30 for the MCE group and 1.97 ± 0.54 for the non-MCE group (p < 0.001). Two-year event-free survival using an optimum H/M ratio threshold of 1.75 was 62% for H/M ratio less than 1.75, 95% for H/M ratio greater than or equal to 1.75 (p < 0.0001). Logistic regression showed H/M ratio and LVEF as the only significant predictors of MCE. Using the lower and upper H/M quartiles of 1.45 and 2.17 as high- and very low-risk thresholds, 2-year event-free survival rates were 52% and 98%, respectively. Among patients with LVEF ≤ 35% and H/M ≥ 1.75 (n = 73), there were nine MCEs because of progressive HF and only one because of an arrhythmia. Conclusion Application of a clinical trial methodology via the retrospective reanalysis of ¹²³I-mIBG images confirms the previously reported prognostic value of this method in HF patients, including potential identification of a quantitative threshold for low risk for cardiac mortality and potentially fatal ventricular arrhythmias.     

Targeting murine heart and brain: visualisation conditions for multi-pinhole SPECT with <Superscript>99m</Superscript>Tc- and <Superscript>123</Superscript>I-labelled probes

Purpose  The study serves to optimise conditions for multi-pinhole SPECT small animal imaging of ¹²³I- and ^99mTc-labelled radiopharmaceuticals with different distributions in murine heart and brain and to investigate detection and dose range thresholds for verification of differences in tracer uptake. Methods  A Triad 88/Trionix system with three 6-pinhole collimators was used for investigation of dose requirements for imaging of the dopamine D₂ receptor ligand [¹²³I]IBZM and the cerebral perfusion tracer [^99mTc]HMPAO (1.2–0.4 MBq/g body weight) in healthy mice. The fatty acid [¹²³I]IPPA (0.94 ± 0.05 MBq/g body weight) and the perfusion tracer [^99mTc]sestamibi (3.8 ± 0.45 MBq/g body weight) were applied to cardiomyopathic mice overexpressing the prostaglandin EP₃ receptor. Results  In vivo imaging and in vitro data revealed 45 kBq total cerebral uptake and 201 kBq cardiac uptake as thresholds for visualisation of striatal [¹²³I]IBZM and of cardiac [^99mTc]sestamibi using 100 and 150 s acquisition time, respectively. Alterations of maximal cerebral uptake of [¹²³I]IBZM by >20% (116 kBq) were verified with the prerequisite of 50% striatal of total uptake. The labelling with [^99mTc]sestamibi revealed a 30% lower uptake in cardiomyopathic hearts compared to wild types. [¹²³I]IPPA uptake could be visualised at activity doses of 0.8 MBq/g body weight. Conclusion  Multi-pinhole SPECT enables detection of alterations of the cerebral uptake of ¹²³I- and ^99mTc-labelled tracers in an appropriate dose range in murine models targeting physiological processes in brain and heart. The thresholds of detection for differences in the tracer uptake determined under the conditions of our experiments well reflect distinctions in molar activity and uptake characteristics of the tracers. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Clinical evaluation of the 99mTc-CPI myocardial perfusion imaging

^99mTc-CPI myocardial perfusion scintigraphy including planar images in 35 patients and SPECT images in 16 patients has been studied. Scintigraphic data revealed that high quality ^99mTc-CPI myocardial perfusion images were obtained. The sensitivity and specificity of ^99mTc-CPI planar images in detecting CAD was 92% and 80% respectively. There was no significant difference in sensitivity for detecting CAD between planar and SPECT. However, the specificity of SPECT was much better than that of planar imaging.     

Regional alterations in myocardial sympathetic innervation in patients with transient left-ventricular apical ballooning (Tako-Tsubo cardiomyopathy)

Background  Excess sympathetic nervous activity was proposed to play a crucial role in the pathogenesis of transient left-ventricular apical ballooning (TLVAB, also known as Tako-Tsubo cardiomyopathy). This study was conducted to assess presynaptic adrenergic alterations in the dysfunctional myocardium of patients with TLVAB. Methods and Results  Ten consecutive patients undergoing coronary angiography for acute coronary syndrome who fulfilled the proposed Mayo Clinic criteria for the diagnosis of TLVAB were investigated. Myocardial iodine-123 metaiodobenzylguanidine (¹²³I-MIBG) studies (planar and single-photon emission computed tomography [SPECT]) were performed to evaluate adrenergic innervation. Concomitantly, myocardial perfusion was assessed by means of technetium-99m methoxyisobutylisonitrile (^99mTc-MIBI) SPECT. In all patients, angiography revealed typical ballooning of the left-ventricular (LV) apex and hyperkinesis of the basal LV segments (overall ejection fraction, 41%±5% [mean±SEM]). Planar ¹²³I-MIBG scans revealed decreased heart-to-mediastinum ratios at early (20 minutes) and delayed (4 hours) images (2.1±0.1 and 1.9±0.1, respectively). The cardiac washout rate of ¹²³I-MIBG on the late images was increased to 34%±3%. The ¹²³I-MIBG uptake on SPECT scans was obviously reduced in the akinetic LV apex (defect score, 3.30±0.34), whereas ^99mTc-MIBI SPECT indicated normal or only mildly reduced perfusion within this region (defect score, 0.89±0.35). Conclusions  Our study indicates a functional alteration in presynaptic sympathetic neurotransmission in patients with TLVAB, and suggests a pathophysiologic explanation of the impairment of LV function.     

Does the Incremental Value of 123I-Metaiodobenzylguanidine SPECT/CT over Planar Imaging Justify the Increase in Radiation Exposure?

PurposePlanar scintigraphy with ¹²³I-radiolabeled metaiodobenzylguanidine (¹²³I-mIBG) is an important imaging modality to evaluate neuroblastoma. In recent years, Single Photon Emission Computed Tomography combined with Computed Tomography (SPECT/CT) has revolutionized nuclear medicine. Nevertheless, the addition of the CT has increased the patients'' irradiation. We aimed to evaluate the incremental benefits of ¹²³I-mIBG SPECT/CT over conventional planar imaging and to estimate the relative increase of radiation dose.MethodsWe retrospectively evaluated the added value of 56 SPECT/CT performed in 40 children in terms of better characterization of the lesion and its locoregional extension, better lymph node staging, detection of new lesions, and elimination of false positives by a paired comparison between the planar images and the SPECT/CT ones. Then, we calculated the percentage contribution of the additional radiation of the CT in this hybrid imagery.ResultsIn 88% (49 out of 56) of the examinations, SPECT/CT provided additional information, which was crucial in 20% of the cases. It allowed a better characterization of the lesion and its locoregional extension in 44 cases, a better lymph node staging in 28 cases, the detection of 33 new lesions, and the elimination of 9 false positives. The CT effective dose was significantly lower than the SPECT one. The average additional radiation exposure due to CT was 12% (4–23%).Conclusion¹²³I-mIBG SPECT/CT has an undeniable added value that improves planar imaging interpretation and impacts patient management. These potential benefits would justify the low additional radiation induced by the CT.     

Radionuclide imaging of cardiac autonomic innervation

Cardiac autonomic function plays a crucial role in health and disease, with abnormalities both reflecting the severity of the disease and contributing specifically to clinical deterioration and poor prognosis. Radiotracer analogs of the sympathetic mediator norepinephrine have been investigated extensively, and are at the brink of potential widespread clinical use. The most widely studied SPECT tracer, I-123 metaiodobenzylguanidine (¹²³I-mIBG) has consistently shown a strong, independent ability to risk stratify patients with advanced congestive heart failure. Increased global cardiac uptake appears to have a high negative predictive value in terms of cardiac events, especially death and arrhythmias, and therefore and may have a role in guiding therapy, particularly by helping to better select patients unresponsive to conventional medical therapies who would benefit from device therapies such as an ICD (implantable cardioverter defibrillator), CRT (cardiac resynchronization therapy), LVAD (left ventricular assist device), or cardiac transplantation. Cardiac autonomic imaging with SPECT and PET tracers also shows potential to assess patients following cardiac transplant, those with primary arrhythmic condition, coronary artery disease, diabetes mellitus, and during cardiotoxic chemotherapy. Radiotracer imaging of cardiac autonomic function allows visualization and quantitative measurements of underlying molecular aspects of cardiac disease, and should therefore provide a perspective that other cardiac tests cannot.     

Influence of 99mTc-tetrofosmin SPECT myocardial perfusion imaging on the prediction of future adverse cardiac events

Background  The impact of myocardial perfusion imaging (MPI) on prediction of risk for future cardiac events was examined by comparing predictions based on clinical information alone and in combination with MPI findings. Methods and Results  A 3-cardiologist Cardiac Event Prediction Panel (CEPP) estimated three-year cardiac event (non-fatal MI; aborted sudden cardiac death; cardiac death) risk based on clinical data (C) for 371 subjects. CEPP repeated this estimation after receiving Summed Stress Scores (SSS) and Summed Rest Scores (SRS) from blinded reading of rest-stress ^99mTc-tetrofosmin MPI SPECT studies (C + MPI). The C and C + MPI estimates were then compared with three-year and total event rates. MPI was normal (SSS ≤ 3) in 227 patients (61%), mildly abnormal (SSS 4-8) in 31 (8%), moderately abnormal (SSS 9-13) in 36 (10%), and severely abnormal (SSS > 13) in 77 (21%). Eighteen cardiac events occurred within 3 years and 33 occurred during a mean follow-up of 3.9 years. C + MPI estimates of low risk (<1-1.5%/year) identified significantly more patients who did not have events than C. C + MPI three-year event-rate predictions were more accurate than those made with C (P < .01). C + MPI categorization also provided better delineation of incremental risk on time-to-event analyses. Conclusions   ^99mTc-tetrofosmin MPI single photon emission computed tomography (SPECT) findings significantly improve accuracy of cardiac event rate prediction compared to those based on clinical information alone. This study was performed by GE Healthcare.     

Role of 99mTc-sestamibi SPECT in accurate selection of primary hyperparathyroid patients for minimally invasive radio-guided surgery

Purpose A prerequisite for optimum minimally invasive radio-guided surgery (MIRS) for primary hyperparathyroidism (PHPT) is the demonstration of significant uptake of ^99mTc-sestamibi in a parathyroid adenoma (PA). The aim of this study was to evaluate the clinical role or ^99mTc-sestamibi SPECT in selecting patients for this procedure. Methods Fifty-four consecutive PHPT patients were evaluated by single-session ^99mTc-pertechnetate/^99mTc-sestamibi planar subtraction scintigraphy, followed by ^99mTc-sestamibi SPECT acquisition to localise hyperfunctioning PAs and assist in planning the surgical approach. Results Scintigraphy showed the presence of a solitary PA in 47/54 patients (87%) and two or more PAs in four patients (7.4%); it was negative in the remaining three patients (5.6%). The overall sensitivity of ^99mTc-sestamibi scintigraphy was 94.6%. In 7/54 patients, the PA was located deep in the para-oesophageal/paratracheal space. So far, 22 patients with scintigraphic evidence of a solitary PA (in four of whom the PA was located deep in the neck) have undergone successful MIRS using the low 37 MBq (1 mCi) ^99mTc-sestamibi dose protocol. Intraoperative quick parathyroid hormone (QPTH) assay demonstrated a fall in all 22 patients, thus confirming successful removal of the hyperfunctioning PA. No major surgical complications were observed. After a period of follow-up ranging between 6 and 27 months (median 13 months), no case of persistent/recurrent PHPT was recorded. When comparing the parathyroid to background (P/B) ratio measured at planar and SPECT preoperative scintigraphy with that measured intraoperatively with the gamma probe, a good linear correlation was found between the SPECT and the intraoperative gamma probe measurements (r=0.89; p<0.01) but no correlation was found with planar scintigraphic data. Conclusion Our preliminary data suggest that measurement of the P/B ratio by means of ^99mTc-sestamibi SPECT is more accurate in predicting the intraoperative measurements with the gamma probe. In this respect, a preoperative ^99mTc-sestamibi SPECT acquisition should be recommended for better selection of PHPT patients in whom a MIRS approach can be offered.     

Use of cardiac radionuclide imaging to identify patients at risk for arrhythmic sudden cardiac death

Sudden cardiac death (SCD) accounts for about ½ of all cardiovascular deaths, in most cases the result of a lethal ventricular arrhythmia. Patients considered at risk are often treated with an implantable cardiac defibrillator (ICD), but current criteria for device use, based largely on left ventricular ejection fraction (LVEF), leads to many patients receiving ICDs that they do not use, and many others not receiving ICDs but who suffer SCD. Thus, better methods of identifying patients at risk for SCD are needed, and radionuclide imaging offers much potential. Recent work has focused on imaging of cardiac autonomic innervation. ¹²³I-mIBG, a norepinephrine analog, is the tracer most studied, and a variety of positron emission tomographic tracers are also under investigation. Radionuclide autonomic imaging may identify at-risk patients with ischemic coronary artery disease, particularly following myocardial infarction and in the setting of hibernating myocardium. Most studies have been done in the setting of congestive heart failure (CHF), with a recent large multicenter study of patients with advanced disease, typically at high risk of SCD, showing that ¹²³I-mIBG can identify a low risk subgroup with an extremely low incidence of lethal ventricular arrhythmias and cardiac death, therefore, perhaps not requiring an ICD. Cardiac neuronal imaging has been shown to be better predictive of lethal arrhythmias/cardiac death than LVEF and New York Heart Association class, as well as various ECG parameters. Autonomic imaging will likely play an important role in the advancement of cardiac molecular imaging.     

<Superscript>123</Superscript>I-Interleukin-2 uptake in squamous cell carcinoma of the head and neck carcinoma

Introduction Information obtained on the IL-2 receptor status of tumour infiltrating lymphocytes in patients suffering from squamous cell carcinoma of the head and neck (SSCHN) before and after IL-2 treatment may lead to a better understanding of the immunological changes and related kinetics induced at the tumour level and ultimately to a strategy that allows selection of those patients that will benefit from IL-2 therapy. This study set out to assess the relationship between ¹²³I-IL2 single-photon emission computed tomography (SPECT) findings and the presence of IL-2 receptors (CD25 staining) on tumour-infiltrating lymphocytes as well as on SCCHN tumour cells in patients suffering from SCCHN. Materials and methods Seventeen consecutive patients (12 men; mean age, 57 years) highly suspected to suffer from SSCHN were prospectively included in the study. All patients underwent planar and whole body ¹²³I-IL2 scintigraphy and underwent surgery or had a biopsy taken within 1 week from imaging. Surgical resected primary lesions as well as biopsy material from primary tumours were histologically analysed with respect to the presence and intensity of CD25 expression on tumour infiltrating lymphocytes and tumour cells (HSCORE). Tumor-to-background (T/N) ratios of the primary tumour derived from planar and tomographic ¹²³I-IL2 scintigraphy were related to the results derived from histology. Results All patients suffered from SSCHN. T/N ratios derived from SPECT images were significantly correlated with CD25 lymphocyte HSCOREs (r = 0.66; p = 0.03), but not with CD25 tumour cell HSCOREs. Conclusions ¹²³I-IL-2 SPECT imaging allows for non-invasive imaging of the relative amount of IL-2 receptors present on tumour infiltrating lymphocytes in SCCHN.     

“Luxury perfusion” with99mTc-HMPAO and123I-IMP SPECT imaging during the subacute phase of stroke

To compare the merits of¹²³I-isopropyl-iodoam-phetamine (¹²³I-IMP) and^99mTc-HMPAO in showing abnormal brain uptake distribution during cerebral ischemia, we studied ten patients during the subacute phase of their stroke, a period where metabolism and blood flow are frequently uncoupled. SPECT imaging was performed using both radiopharmaceuticals in the 10 patients from 48 h to 4 weeks after onset of symptoms. Two patients out of the 10 had similar defects with¹²³I-IMP and^99mTc-HMPAO SPECT, the location of the defects corresponding to the area of infarction observed on CT. Six patients had normal^99mTc-HMPAO SPECT and abnormal¹²³I-IMP SPECT with defects in the area of infarction shown by CT. The remaining 2 patients had hyperactive abnormalities on^99mTc-HMPAO in areas corresponding to defects on the¹²³I-IMP images. Two of the patients with SPECT mismatches were studied again more than 1 month after onset. On reexamination,^99mTc-HMPAO SPECT which was previously normal or hyperactive became hypoactive with a focal area of decreased activity corresponding to the defect on¹²³I-IMP. Crossed cerebellar diaschisis was found in 7 patients with^99mTc-HMPAO and was absent for both¹²³I-IMP and^99mTc-HMPAO in 3. We suggest that SPECT with⁹⁹mTc-HMPAO could show transient hyperemia not demonstrated by¹²³I-IMP whereas in some cases cerebral infarction would be more difficult to demonstrate with^99mTc-HMPAO than with¹²³I-IMP. SPECT with both tracers is recommended to follow the evolution of strokes in terms of regional cerebral blood flow and tissue metabolism.     

The scintigraphic evaluation of myocardial infarction and regional ventricular performance using technetium-99m hexakis (t-butylisonitrile) technetium (I) (TBI): A new myocardial imaging agent

Technetium-99m hexakis (t-butylisonitrile) technetium (I) (^99mTc-TBI) is a new myocardial perfusion imaging agent. To determine its potential in the evaluation of myocardial infarction, 15 patients with suspected or confirmed acute infarction were studied by bedside imaging in the coronary care unit. Good-quality planar scintigrams in multiple projections were obtained in 13 patients. Gated perfusion studies were performed in 14 patients, and for comparison 13 of these were restudied 24–72 h later by standard gated equilibrium blood pool radionuclide ventriculography. Conventional and planar scintigraphic criteria for myocardial infarction (acute or old) agreed in 12 (92%) patients (k=0.81, p<0.05). All the infarctions detected by scintigraphy were associated with electrocardiographic Q-waves. Localization of infarction by the electrocardiogram and scintigraphy exhibited moderate agreement (k=0.49, p<0.1). Regional wall motion analysis by standard radionuclide ventriculography and gated ^99mTc-TBI scintigraphy were in complete agreement for 25 (64%) of 39 left ventricular segments (k=0.35, p<0.05). However, in 7 other segments, associated with areas of infarction, regional wall motion abnormalities were noted only on gated ^99mTc-TBI scintigraphy. Therefore, ^99mTc-TBI scintigraphy can readily provide data on regional myocardial perfusion and wall motion, permitting detection and localization of areas of myocardial infarction. The superior imaging properties, ready availability and low cost of ^99mTc point to the considerable potential value of ^99mTc-TBI in assessing patients with suspected or confirmed myocardial infarction.This work was done during the tenure of a British-American Research Fellowship of the American Heart Association and the British Heart Foundation, with Dr. S. Campbell the recipient     

Incremental prognostic value of dobutamine–atropine stress 99mTc-tetrofosmin myocardial perfusion imaging for predicting outcome in diabetic patients with limited exercise capacity

Purpose This study assessed the incremental value of dobutamine stress ^99mTc-tetrofosmin single-photon emission computed tomography (SPECT) for the prediction of cardiac events in diabetic patients with limited exercise capacity.Methods The study population comprised 125 consecutive diabetic patients (mean age 61±9 years, 61% men) who were unable to perform an exercise test and underwent dobutamine ^99mTc-tetrofosmin SPECT. Follow-up was successful in 124 (99%) patients. Three patients who underwent early revascularisation (within 60 days) were excluded. End-points during follow-up were cardiac death and non-fatal myocardial infarction.Results An abnormal scan (with the presence of reversible or fixed perfusion defects) was observed in 76 (63%) patients. During the follow-up (3.4±1.5 years), 36 patients died (19 cardiac deaths) and four patients had non-fatal myocardial infarction. Cardiac death occurred in one of 49 (2%) patients with a normal myocardial perfusion study and in 18 of 75 (24%) patients with an abnormal study (p<0.001). Abnormal scan was incremental to the clinical parameters in predicting cardiac death (²=48 vs 39, p<0.05) and hard cardiac events (²=50 vs 43, p<0.05).Conclusion Dobutamine stress ^99mTc-tetrofosmin SPECT provides prognostic information additional to clinical data for the prediction of cardiac death and hard cardiac events in diabetic patients unable to perform an exercise test.     

Influence of myocardial region of interest definition on quantitative analysis of planar 123I-mIBG images

Purpose

In planar ¹²³I-mIBG myocardial imaging, definition of the heart region of interest (ROI) is a critical step in quantifying uptake. The present study evaluated the impact of changes in heart ROI size on quantitative results in subjects with good and poor uptake.

Methods

Reference irregular whole-heart and square upper mediastinum ROIs were defined visually on 531 planar ¹²³I-mIBG images. Based on the reference heart ROI, an automated program created two other ROIs: one larger (+1 pixel) and one smaller (?1 pixel), the stated numbers representing the spacing intervals between each epicardial boundary pixel. Two additional smaller ROIs (?2 and ?3 pixels) were drawn for the 100 images (19 %) with a heart/mediastinum (H/M) ratio ≤1.30. The number of pixels, the counts per pixel, and the H/M ratio for each heart ROI were calculated and compared to that in the reference ROI. Washout rate and changes as a function of ROI size were also calculated for 110 subjects who had both early and late images.

Results

The mean changes in heart ROI size ranged from +19.0 % for the +1 pixel to ?44.4 % for the ?3 pixels ROI. For the +1 and ?1 pixel ROIs, mean relative counts per pixel changes were ?1.2 % and +0.7 %, respectively, with corresponding ranges of change in the H/M ratio of ?0.12 to +0.05 and ?0.05 to +0.11. For scans with H/M ratio ≤1.30, mean relative counts per pixel changes were 0, 0, ?0.7 %, and ?1.4 % for the four ROIs, with range of change in the H/M ratio from ?0.13 to +0.05. Mean washout rates were almost identical for the reference ROIs (45.0 %) and the +1 pixel and ?1 pixel heart ROIs (44.9 % and 45.1 %, respectively).

Conclusion

Significant changes in the size of the best visually defined heart ROI produce minimal, clinically inconsequential changes in the H/M ratio and washout rate, even in subjects with significantly reduced myocardial uptake of ¹²³I-mIBG.     

Dopamine transporter imaging with [123I]FP-CIT SPECT: potential effects of drugs

Background [¹²³I]N-ω-fluoropropyl-2β-carbomethoxy-3β-{4-iodophenyl}nortropane ([¹²³I]FP-CIT) single photon emission computed tomography (SPECT) is a frequently and routinely used technique to detect or exclude dopaminergic degeneration by imaging the dopamine transporter (DAT) in parkinsonian and demented patients. This technique is also used in scientific studies in humans, as well as in preclinical studies to assess the availability of DAT binding in the striatum. In routine clinical studies, but also in scientific studies, patients are frequently on medication and sometimes even use drugs of abuse. Moreover, in preclinical studies, animals will be anesthetized. Prescribed drugs, drugs of abuse, and anesthetics may influence the visual interpretation and/or quantification of [¹²³I]FP-CIT SPECT scans. Discussion Here, we discuss the basic principle of how drugs and anesthetics might influence the visual interpretation and/or quantification of [¹²³I]FP-CIT SPECT scans. We also review drugs which are likely to have a significant influence on the visual interpretation and/or quantification of [¹²³I]FP-CIT SPECT scans. Additionally, we discuss the evidence as to whether frequently prescribed drugs in parkinsonian and demented patients may have an influence on the visual interpretation and/or quantification of [¹²³I]FP-CIT SPECT scans. Finally, we discuss our recommendations as to which drugs should be ideally withdrawn before performing a [¹²³I]FP-CIT SPECT scan for routine clinical purposes. The decision to withdraw any medication must always be made by the specialist in charge of the patient’s care and taking into account the pros and cons of doing so.