Single Photon Emission Computed Tomography Techniques Research Articles

Molecular and cellular imaging of the eye.

The application of molecular and cellular imaging in ophthalmology has numerous benefits. It can enable the early detection and diagnosis of ocular diseases, facilitating timely intervention and improved patient outcomes. Molecular imaging techniques can help identify disease biomarkers, monitor disease progression, and evaluate treatment responses. Furthermore, these techniques allow researchers to gain insights into the pathogenesis of ocular diseases and develop novel therapeutic strategies. Molecular and cellular imaging can also allow basic research to elucidate the normal physiological processes occurring within the eye, such as cell signaling, tissue remodeling, and immune responses. By providing detailed visualization at the molecular and cellular level, these imaging techniques contribute to a comprehensive understanding of ocular biology. Current clinically available imaging often relies on confocal microscopy, multi-photon microscopy, PET (positron emission tomography) or SPECT (single-photon emission computed tomography) techniques, optical coherence tomography (OCT), and fluorescence imaging. Preclinical research focuses on the identification of novel molecular targets for various diseases. The aim is to discover specific biomarkers or molecular pathways associated with diseases, allowing for targeted imaging and precise disease characterization. In parallel, efforts are being made to develop sophisticated and multifunctional contrast agents that can selectively bind to these identified molecular targets. These contrast agents can enhance the imaging signal and improve the sensitivity and specificity of molecular imaging by carrying various imaging labels, including radionuclides for PET or SPECT, fluorescent dyes for optical imaging, or nanoparticles for multimodal imaging. Furthermore, advancements in technology and instrumentation are being pursued to enable multimodality molecular imaging. Integrating different imaging modalities, such as PET/MRI (magnetic resonance imaging) or PET/CT (computed tomography), allows for the complementary strengths of each modality to be combined, providing comprehensive molecular and anatomical information in a single examination. Recently, photoacoustic microscopy (PAM) has been explored as a novel imaging technology for visualization of different retinal diseases. PAM is a non-invasive, non-ionizing radiation, and hybrid imaging modality that combines the optical excitation of contrast agents with ultrasound detection. It offers a unique approach to imaging by providing both anatomical and functional information. Its ability to utilize molecularly targeted contrast agents holds great promise for molecular imaging applications in ophthalmology. In this review, we will summarize the application of multimodality molecular imaging for tracking chorioretinal angiogenesis along with the migration of stem cells after subretinal transplantation in vivo.

Evaluation of Left Ventricle Performance in Patients with Ischemic Heart Disease Using Single Photon Emission Computed Tomography (SPECT) in Comparison with Echocardiography

Background: Ischemic heart disease is a major cause of the diastolic heart failure. Risk of heart failures was increased with microvascular coronary disease, which is characterized by left ventricular stiffness with impaired relaxation and reduced compliance. Aim of this study is to estimate the effect of the severity of myocardium ischemia on the left ventricle ejection fraction and left ventricular volume using SPECT with 99mTc MIBI and to compare the results with the echocardiography. The study included 117 subjects with ischemic heart disease were examined using SPECT and echocardiography techniques. The following parameters were measured: left ventricular end systolic volume (LVESV) , left ventricular end diastolic volume (LVEDV) , and left ventricular ejection fraction (LVEF). Results show that the change difference in EDV between the two technique was (98.79%) with insignificant (p > 0.05). While the change in the LVEF% between both groups was (105.40%) with significant (p <0.05). On the other hand, the difference in ESV and EDV/ESV ratio for both groups were (95.52%), and (103.61%) respectively with insignificant (p >0.05). It was concluded that SPECT with 99mTc MIBI had a good relation with the echocardiography technique for evaluation of the left ventricular ejection fraction and the left ventricular volumes. The results showed that LVEF was decreased in patients with severe ischemic disease.

Diagnostic Accuracy of 64-Slice Computed Tomography Angiography in Patients with Chest Pain vs. SPECT in the Assessment of Significant Coronary Artery Disease: A Systematic Review and Meta-analysis

Context: This systematic review and meta-analysis intended to investigate the diagnostic accuracy of computed tomography angiography (CTA) in comparison with single-photon emission computed tomography (SPECT) for the diagnosis of coronary artery disease (CAD) in chest pain patients with no history of cardiovascular diseases (CVDs).
 Methods: Invasive angiography was considered as the reference test with a stenosis threshold of ≥ 50%. Cochrane, Scopus, Science Direct, PubMed, and Embase databases were comprehensively searched from the time of inception of these databases to May 15, 2018. A manual search in Google Scholar, a reference review of the obtained studies, and a review of gray literature (including those presented in conferences and congresses) regarding diagnostic performances of CTA and SPECT techniques were performed independently by two researchers. A meta-analysis was performed to determine pooling estimates of sensitivity, specificity, diagnostic odds ratio, and positive as well as negative likelihood ratios in CTA and SPECT tests. According to the 2 × 2 contingency table of each study, at 0.95 confidence interval, the diagnostic accuracy of CTA and SPECT was meta-analyzed by pooling estimates of sensitivity, specificity, diagnostic odds ratio (DOR), and positive and negative likelihood ratios based on DerSimonian-Laird’s random-effects model. Heterogeneity was assessed by calculating I2. Analyses were performed using MetaDiSc version 1.4 and Stata version 11. The qualities of the selected studies were assessed independently by two researchers according to the quality assessment of diagnostic accuracy studies (QUADAS) questionnaire. Sensitivity analyses were performed by the Jackknife method. Publication bias was evaluated by Deeks’ funnel plot.
 Results: Fourteen studies related to CTA (1206 individuals) and 15 related to SPECT (1638 individuals) were eligible for meta-analysis. The pooled sensitivity and the specificity of CTA for CAD diagnosis were 91% (95% CI, 88% - 94%) and 87% (95% CI, 84% - 98%), respectively. The pooled positive and negative likelihood ratios, the diagnostic odds ratio, and the area under the ROC curve for CTA were 7.93 (95% CI, 5.11 - 12.29), 0.1 (95% CI, 0.06 - 0.17), 95.71 (95% CI, 59.81 - 153.15), and 0.96, respectively. The pooled sensitivity and the specificity of SPECT for CAD diagnosis were 81% (95% CI, 79% - 83%) and 74% (95% CI, 71% - 78%), respectively. The pooled positive and negative likelihood ratios, the diagnostic odds ratio, and the area under the ROC curve for SPECT were 3.03 (95% CI, 2.34 - 3.91), 0.25 (95% CI, 0.21 - 0.30), 13.56 (95% CI, 10.60 - 12.34), and 0.86, respectively. According to the sensitivity analyses, the removal of any single study at a time did not change the effect size of the remaining studies. We observed symmetry in the Deeks’ funnel plot, indicating that there was ignorable publication bias for CTA and SPECT studies.
 Conclusions: This study demonstrated that the diagnostic accuracies of CTA and SPECT tests lie in the ‘excellent’ and the ‘very good’ ranges, respectively. CTA is stronger evidence, than SPECT, to rule out CVDs in patients with low and intermediate risks of CAD with no history of cardiovascular diseases.

Use of quantitative SPECT/CT reconstruction in 99mTc-sestamibi imaging of patients with renal masses.

Technetium-99m (99mTc)-sestamibi single-photon emission computed tomography/computed tomography (SPECT/CT) has previously been shown to allow for the accurate differentiation of benign renal oncocytomas and hybrid oncocytic/chromophobe tumors (HOCTs) apart from other malignant renal tumor histologies, with oncocytomas/HOCTs showing high uptake and renal cell carcinoma (RCC) showing low uptake based on uptake ratios from non-quantitative single-photon emission computed tomography (SPECT) reconstructions. However, in this study, several tumors fell close to the uptake ratio cutoff, likely due to limitations in conventional SPECT/CT reconstruction methods. We hypothesized that application of quantitative SPECT/CT (QSPECT) reconstruction methods developed by our group would provide more robust separation of hot and cold lesions, serving as an imaging framework on which quantitative biomarkers can be validated for evaluation of renal masses with 99mTc-sestamibi. Single-photon emission computed tomography data were reconstructed using the clinical Flash 3D reconstruction and QSPECT methods. Two blinded readers then characterized each tumor as hot or cold. Semi-quantitative uptake ratios were calculated by dividing lesion activity by background renal activity for both Flash 3D and QSPECT reconstructions. The difference between median (mean) hot and cold tumor uptake ratios measured 0.655 (0.73) with the QSPECT method and 0.624 (0.67) with the conventional method, resulting in increased separation between hot and cold tumors. Sub-analysis of 7 lesions near the separation point showed a higher absolute difference (0.16) between QPSECT and Flash 3D mean uptake ratios compared to the remaining lesions. Our finding of improved separation between uptake ratios of hot and cold lesions using QSPECT reconstruction lays the foundation for additional quantitative SPECT techniques such as SPECT-UV in the setting of renal 99mTc-sestamibi and other SPECT/CT exams. With robust quantitative image reconstruction and biomarker analysis, there may be an expanded role for SPECT/CT imaging in renal masses and other pathologic conditions.

Brain SPECT with Perfusion Radiopharmaceuticals and Dopaminergic System Radiocompounds in Dementia Disorders.

As well known, the increase in life expectancy and the better physical condition of people in western countries will lead in the next 20 years to a dramatic development of neurodegenerative diseases, especially of dementia that could be considered one of the most important problems in clinical, social and economic fields for the future. Therefore, the differential diagnosis of the various types of dementia is a critical step for patients, clinicians and researchers since an accurate "in vivo" diagnosis can lead to a better patients management. Neuroimaging techniques and in particular the most diffuse and affordable single photon emission computed tomography (SPECT) have provided useful information about dementia disorders and these methods, on the basis of the recent advances, will have an increasingly important role in research and clinical practice. The purpose of this article is to analyze the different SPECT techniques now available which proved clinically useful in correctly formulating the differential diagnosis of dementia.

Depression, anxiety, and apathy in Parkinson's disease: insights from neuroimaging studies.

Depression, anxiety and apathy are common mood disturbances in Parkinson's disease (PD) but their pathophysiology is unclear. Advanced neuroimaging has been increasingly used to unravel neural substrates linked to these disturbances. A systematic review is provided of neuroimaging findings in depression, anxiety and apathy in PD. A PubMed, MEDLINE and EMBASE search of peer‐reviewed original research articles on these mood disturbances in PD identified 38 studies on depression, eight on anxiety and 14 on apathy in PD. Most of the imaging studies used either position emission tomography or single‐photon emission computed tomography techniques. These studies generally suggest increased neural activity in the prefrontal regions and decreased functional connectivity between the prefrontal−limbic networks in depressed patients. Functional imaging studies revealed an inverse correlation between dopaminergic density in the caudate and putamen with the severity of anxiety in PD. There was no consistent correlation between dopaminergic density of thalamus and anxiety. Studies demonstrated both positive and inverse correlations between apathy and metabolism or activity in the striatum, amygdalar, prefrontal, temporal and parietal regions. The clinical variability of study subjects and differences in image pre‐processing and analytical strategies may contribute to discrepant findings in these studies. Both nigrostriatal and extra‐nigrostriatal pathways (in particular the frontal region and its connecting areas) are affected in mood disorders in PD. Identifying the relative contributions of these neural pathways in PD patients with overlapping motor and mood symptoms could provide new pathophysiological clues for the development of better therapeutic targets for affected patients.

Imaging in Aerosol Medicine.

Imaging techniques have been used extensively to study the delivery of inhaled medications. Deposition scintigraphy involves the quantification of deposited aerosol dose and is performed using 2-dimensional planar or 3-dimensional positron emission tomography (PET) or single-photon-emission computed tomography (SPECT) imaging techniques. Planar techniques have an extensive history of use, and quantification methods are well established. SPECT and PET techniques can provide better dose localization, but quantification is more complex, and the techniques are in more limited use. Aerosols have also been used to deliver radiopharmaceutical probes for the imaging of lung physiology. These studies include measurements of ventilation, mucus and cough clearance, and, more recently, liquid absorption in the airways. Clearance measurements have been used to assess therapeutic response in conditions such as cystic fibrosis. Future directions in aerosol-based imaging are likely to include use of novel probes to measure new physiological processes in the lung, more thorough integration of anatomical imaging, and use of multiple probes to simultaneously image drug and disease or interacting physiological processes.

Noninvasive Stem Cell Labeling Using USPIO Technique and their Detection with MRI

Background: To date, several imaging techniques to track stem cells are used such as positron emission tomography (PET), single photon emission computed tomography (SPECT), Bioluminescence imaging (BLI), fluorescence imaging, CT scan and magnetic resonance imaging (MRI). Although, overall sensitivity of MRI compared to SPECT and Bioluminescence techniques are lower, but due to high spatial resolution (~100 mm), long term three-dimensional imaging capability, in vivo quick access to images in three different sections, and noninvasiveness it is being used as the method of choice. Methods: The present study is the search results for authors and sources of information in the field of molecular and cellular imaging to examine the problems and perspectives about stem cells labeling with Ultrasmall Super Paramagnetic Iron Oxide (USPIO) and their tracking by MRI. Results: With the advancement of technology, including quantum physics, chemistry, and computer software, MRI with an excellent spatial resolution and contrast, is surpasses other imaging modalities in the analysis of anatomical and pathological features and images of all body tissues. From the other side, advances in the astronomical science, chemistry and nanotechnology, high biocompatibility and cytotoxicity of nanoparticles, and due to analysis in the metabolic pathways of iron made the procedure easier; however, there are still several fundamental questions in understanding the mechanism of biological molecules in the living cells including: 1- How to detect not only the location but also the performance of the labeled cells? Probably combination of USPIO nanoparticles with other reporter genes as contrast agents for MRI and PET can simultaneously be used to overcome these limitations 2) How to trace stem cells from pre-clinical models to translate to humans? Up to now, due to issues of bioethics, little studies have been done in this area. 3) Whether the transplanted stem cells that have reached the target tissue, will remain or migrate? Despite the fact that cell proliferation and exocytosis are two main factors for long term protection of USPIO nanoparticles inside cells, their signals cannot be received for a long time. 4) What mechanisms cause stem cells reaching the target tissue to react with their environment? And 5) what is the number of transplanted cells in live tissue, and what is their half-life? Conclusion: This study showed that USPIO nanoparticles can enter the cell with a clear dose without any adverse biological effects and could be detected by SWI and T2* techniques under MRI (1.5 Tesla) scanner for almost one month. MRI as a secure mean can illustrate with optimal resolution the spatial-resolution and three-dimensional positions of the stem cells. Keywords: Ultrasmall Super Paramagnetic Iron Oxide (USPIO), labeled stem cell, in vivo tracking, MRI.

The role of SPECT imaging of the dopaminergic system in translational research on Parkinson's disease

Imaging of the dopaminergic system with single photon emission computed tomography (SPECT), and particularly of the dopamine transporter (DAT) located in the striatum, is a well accepted tool in clinical practice to confirm or exclude loss of nigrostriatal dopamine (DA) neurons in patients suspected to suffer from Parkinson's disease (PD). SPECT techniques were developed successfully to image neurotransmitter systems, including the presynaptic DAT and postsynaptic dopamine D2/3 receptors, in rat and mouse models of PD. Here we review the results of preclinical SPECT studies of the dopaminergic system in rat and mouse models of PD. Initially, SPECT studies in animal models of PD were performed to validate that micro-SPECT is able to accurately assess parts of the dopaminergic system in small animals in-vivo. However, more recently, micro-SPECT DAT is increasingly used as a research tool to support the interpretation of human DAT SPECT studies in PD, including clinical trials examining the effects of potential neuroprotective drugs. Translational research with SPECT is an interesting development which may further increase our understanding of the pathophysiology and treatment of PD.

Skeletal muscle satellite cell migration to injured tissue measured with111In-oxine and high-resolution SPECT imaging

The delivery of adult skeletal muscle stem cells, called satellite cells, to several injured muscles via the circulation would be useful, however, an improved understanding of cell fate and biodistribution following their delivery is important for this goal to be achieved. The objective of this study was to evaluate the ability of systemically delivered satellite cells to home to injured skeletal muscle using single-photon emission computed tomography (SPECT) imaging of (111)In-labeled satellite cells. Satellite cells labeled with (111)In-oxine and green fluorescent protein (GFP) were injected intravenously after bupivicaine-induced injury to the tibialis anterior muscle. Animals were imaged with a high-resolution SPECT system called FastSPECT II for up to 7 days after transplantation. In vivo FastSPECT II imaging demonstrated a three to five-fold greater number of transplanted satellite cells in bupivicaine-injured muscle as compared to un-injured muscle after transplantation; a finding that was verified through autoradiograph analysis and quantification of GFP expression. Satellite cells also accumulated in other organs including the lung, liver, and spleen, as determined by biodistribution measurements. These data support the ability of satellite cells to home to injured muscle and support the use of SPECT and autoradiograph imaging techniques to track systemically transplanted (111)In labeled satellite cells in vivo, and suggest their homing may be improved by reducing their entrapment in filter organs.

Multimodality Imaging of CXCR4 in Cancer: Current Status towards Clinical Translation

CXCR4 has gained tremendous attention over the last decade, since it was found to be up-regulated in a wide variety of cancer types, in addition to its role in human immunodeficiency virus infection. Molecular imaging of CXCR4 with small molecules, peptides, and antibodies has been a vibrant research area over the last several years. In this review article, we will summarize the current status of imaging CXCR4 with fluorescence, bioluminescence, positron emission tomography, and single-photon emission computed tomography techniques. Since each molecular imaging modality has its own strengths and weaknesses, dualmodality probes that can be detected by more than one imaging techniques have also been investigated. Noninvasive visualization of CXCR4 expression has potential clinical applications in multiple facets of patient management. While big strides have been made over the last several years in the development of CXCR4- targeted imaging probes, clinical translation and investigation of these agents in cancer patients are eagerly awaited. Since CXCR4 is also involved in many other diseases beyond cancer, these clinically translatable probes can also play multiple roles in other pathological disorders such as myocardial infarction and several immunodeficiency disorders.

Increased Synaptic Dopamine in the Putamen in Restless Legs Syndrome

Prior studies using positron emission tomography (PET) or single-photon emission computed tomography techniques have reported inconsistent findings regarding differences between patients with restless legs syndrome (RLS) and control patients in the striatal dopamine-2 receptor (D2R) binding potentials (BP). D2R-BP does reflect receptor-ligand interactions such as receptor affinity (K(d)) and density (β(max)) or neurotransmitter synaptic concentrations. Thus, differences in D2R-BP reflect changes in these primary factors. PET techniques are currently available to estimate D2R β(max) and K(d). Separate morning and evening PET scans were performed. The D2R-BP were measured in basal ganglia using [(11)C]raclopride. Academic medical center. Thirty-one patients with primary RLS and 36 age- and sex-matched control patients completed the study. Patients with RLS had lower D2R-BP in putamen and caudate but not the ventral striatum. A subgroups analysis of those RLS patients who had not previously taken dopaminergic medications continued to show a significantly lower D2R-BP in the posterior putamen. D2R-BP did not differ between night and day for either group. D2R β(max) and K(d) did not differ significantly between patients with RLS and control patients but did show a strong and significant increase at night in the ventral striatum. Primary and secondary clinical measures of disease status failed to show any relation to D2R in any brain region. Given the lack of any difference in either β(max) or K(d) and the prior studies supporting an increase in presynaptic dopaminergic activity, the current changes found in D2R-BP likely reflect an increase in synaptic dopamine.

Will the new advantages provided by PET in myocardial perfusion imaging help nuclear cardiology survive the test of time against conventional radiological techniques?

Dear Sir, In a very interesting article published in the European Journal of Nuclear Medicine and Molecular Imaging [1], Flotats et al. provide reasonable and interesting findings about the use of Rb PET in the evaluation of patients with and without coronary artery disease (CAD). It is widely accepted that, due to the small risk of complications related to conventional coronary angiography, which has up to now been the gold standard for detecting CAD, noninvasive cardiac imaging is now central to the diagnosis and management of patients with known or suspected CAD. Nuclear cardiology has played an important role in recent years: single-photon emission computed tomography (SPECT) myocardial perfusion imaging (MPI) has been widely validated for the diagnosis and prognosis of cardiac disease, and the technique is heavily embedded in national and international guidelines [2]. In recent years, after a long period dominated by SPECT imaging, the availability of promising perfusion PET tracers such as Rb (1995) and, more recently, N-ammonia has led to various studies comparing PET and SPECT techniques. Although data obtained more than 15 years ago support the superiority of PET over SPECT for diagnosing CAD, it is unclear whether PET would still be found to be superior because of major advances in SPECT instrumentation [3] and imaging protocols [4]. The excellent work by Flotats et al., although comparing PET with standard protocol SPECT acquisition, seems to indicate that PET perfusion imaging may be a better weapon to help nuclear cardiology survive the test of time. It is undoubtedly clear that more recently cardiac magnetic resonance (CMR) may be able to play an important role in CAD detection and evaluation. During a reasonably short acquisition time (on average 45–60 min) CMR may offer a comprehensive cardiac assessment, including qualitative and quantitative functional analysis, detection of valve anomalies, accurate demonstration of infarct size and identification of inducible ischaemia [5]. Information from scanning the heart during pharmacologically induced stress is also provided. With regard to the other noninvasive techniques, a range of agents (i.e. dobutamine, adenosine, dipyridamole) are available, but adenosine is the most widely used because major cardiac events are rare and because the short half-life of the drug allows easier and safer management of patients both under normal conditions and in the event of adverse events. After the administration of adenosine, inducible ischaemia may be indirectly heralded by the onset of regional wall motion abnormalities demonstrated by the acquisition of cine MR images; however, the sensitivity of this technique is quite poor. More commonly, the effects of adenosine are directly assessed through the acquisition of a stack of images with high temporal resolution (typically one image every heartbeat) during the first pass of a bolus of gadolinium-based contrast agent. Although a compromise must be reached between temporal resolution, spatial resolution and image coverage, on modern scanners stress perfusion may be assessed in at least three short-axis sections. When the patient’s heart rate allows it, one or two long-axis sections F. Caobelli (*) : C. Pizzocaro :U. P. Guerra Department of Nuclear Medicine, Fondazione Poliambulanza, Via Bissolati 57, 25100 Brescia, Italy e-mail: fedefournier@libero.it

Evaluation of right ventricular volume and function by 2D and 3D echocardiography compared to MRI

Radionuclide techniques, and recently MRI, have been used for clinical evaluation of right ventricular (RV) volumes function (RVEF) and volumes; but with the introduction of 3D echocardiography, new echocardiographic possibilities for RV evaluation independent of geometrical assumptions have emerged. This study compared classic and new echocardiographic and radionuclide estimates, including gated blood pool single-photon emission computed tomography (SPECT) of RV size and function to RV volumes, and ejection fraction (RVEF) measured by magnetic resonance imaging (MRI). Thirty-four subjects with (a) prior inferior ST-elevation myocardial infarction (n=17), (b) a history of pulmonary embolism and persistent dyspnea (n=7) or (c) normal subjects (n=10) had 2D and 3D echocardiography, SPECT and MRI within 24h. End-diastolic volume and peak tricuspid regurgitation velocity were increased in patients with a history of pulmonary embolism compared to healthy subjects, 130+/-26 ml vs. 94+/-26 ml, P<0.05, and 3.3+/-1.1m/s vs. 2.3+/-0.3m/s, P<0.05, respectively, whereas no differences in RVEF were seen in the three groups. Echocardiographic as well as SPECT estimates of RV volume showed significant correlation to RV volumes by MRI. Tricuspid annular plane systolic excursion (TAPSE) had the better correlation to RVEF by MRI, r=0.48, P<0.01; whereas 3D echocardiography had a correlation of 0.42, P<0.05. Compared to MRI, 3D echocardiography underestimated RVEF by 5.9%, 95% limits of agreement 1.6-10.2%. 3D echocardiographic estimates of RV size and RVEF show only moderate correlation to MRI measures of these parameters, and simple 2D echocardiographic estimates of RV size and function show similar correlations. For routine clinical purposes the simple TAPSE may be preferred over 3D and SPECT techniques for RVEF estimation.

The 17th International IRIST Congress Proceedings

The 17th IRIST (International Research Group on Immunoscitigraphy and Therapy) meeting was held July 27-29, 2004, at the Ghent University Hospital, Ghent, Belgium. Cochairs Christophe Van de Wiele and Alberto Signore brought together basic researchers, clinicians, radiopharmacists, and nuclear medicine specialists to discuss progress in single photon emission computed tomography (SPECT) and positron emission tomography (PET), using radiolabeled antibodies and peptides for imaging biologic properties related to the effectiveness of available treatment options and for treatment of cancer patients. The format of the conference was the presentation of research that focused on the basic and translational biology of cancer and on current state-of-the-art radiopharmacy and related SPECT and PET imaging techniques for the purposes described above. This report summarizes the 17th International IRIST Congress.

Oncological molecular imaging: nuclear medicine techniques

With the expanding interest and development in molecular biology, nuclear medicine imaging, essentially a molecular imaging technique studying biological processes at the cellular and molecular level, has much to offer. As other non-isotope techniques develop there has also been an opportunity for nuclear medicine to broaden its horizons in this field. Nuclear medicine’s involvement in molecular imaging has been enhanced by the improvement in single photon emission computed tomography (SPECT), the wider availability of positron emission tomography (PET) and a greater input and new developments in radiochemistry. Nuclear medicine can be regarded as a method by which biological processes may be non-invasively monitored by radiopharmaceuticals delivered in tracer amounts. By measuring radioactive concentrations in tissue samples, either directly or by means of imaging, it is possible to explore and quantify biological processes in health and disease at the molecular or cellular level. The major advantage of nuclear medicine methods is that only picomolar concentrations of radiotracers are required to provide a measurable signal without interfering with the process under investigation. It is often true that biochemical or metabolic changes can therefore be identified before a significant change in structure or anatomy can be determined. In oncology this has the potential advantage of not only being able to detect abnormal function related to malignant tissue at diagnosis but also to identify changes as a result of therapy earlier than is possible with anatomical techniques alone. However, this high sensitivity is often at the expense of inferior spatial resolution. Here PET techniques show advantages over SPECT, as not only is spatial resolution better, but positron emitting radionuclides include isotopes of carbon (C), nitrogen (N) and oxygen (O), allowing radiolabelling of biological compounds of interest. SPECT relies more frequently on the use of radiolabelled analogues. The spatial resolution of PET remains inferior to that of anatomical techniques including CT, MRI and ultrasound but with the advent of combined dual-modality scanners, such as PET/CT, it is possible that some of the disadvantages of the two techniques may be minimized and the advantages maximized. Another potential disadvantage of SPECT and PET techniques is that the measured signal is not chemically specific; for example, it is not possible to differentiate signal between the administered radiopharmaceutical and its metabolites without more complex metabolite analysis in blood. Due to the spatial resolution advantages of PET over SPECT, coupled with an ability to more accurately correct for attenuation of photons, quantitative accuracy is superior with PET. Absolute measurements of radioactive concentrations in tissue over time allow the measurement of dynamic processes in absolute units such as ml min ml. Realistic goals of nuclear medicine in oncological molecular imaging are to develop high affinity, high specific activity radiopharmaceuticals, allowing quantitation of molecular processes in whole tumour in a reproducible and repeatable manner. In oncology there are a number of areas where nuclear medicine techniques may give information on molecular and cellular events, many of which are already absorbed into routine clinical practice and others that are at a more developmental stage. These applications include the detection and measurement of a number of events in untreated tumours, including glycolysis, proliferation, membrane synthesis and receptor expression, amongst many others. In treated tumours there are methods to nonspecifically measure the downstream effect of cytotoxic therapies but with the development of molecular therapies targeting specific aspects of cancer cell biology there is a greater interest in the development of markers aimed at specifically measuring the molecular consequence of each therapeutic agent. For example, a marker to measure the amount of tumour angiogenesis is likely to be a more sensitive measure of response to an antiangiogenic agent than a non-specific marker of downstream effects such as tumour cell viability. Molecular imaging techniques may also allow us to tailor therapy to individual patients. Visualization of specific molecular targets prior to therapy may identify patients most likely to benefit from a particular molecular therapy. Many novel anticancer therapies are cytostatic rather than cytotoxic and conventional methods of measuring treatment response may be particularly insensitive when tumour shrinkage is not anticipated but where functional changes may be marked. It is here that nuclear medicine techniques also have a role to play and it is important that molecular imaging techniques are developed in conjunction with molecular therapeutics for some of the reasons stated above. Additionally, in nuclear medicine there is the opportunity to label specific molecular probes with a or b emitting radionuclides to deliver a therapeutic dose of targeted radiation to abnormal cells that concentrate these radiopharmaceuticals whilst minimizing radiation dose to normal tissues.

Which are the most used radionuclides in the pet and in the spect techniques in the world?

AbstractThe images in nuclear medicine are mainly obtained through the SPECT (single photon emission computed tomography) and the PET (positron‐emission tomography). These procedures have been carried out with various radionuclides. Here, we have evaluated which are the most used radionuclides in the PET and in the SPECT techniques in the world. We identified the radionuclides cited in the abstracts of two important meetings occured in 2000: “The Society of Nuclear Medicine Meeting (SNM)” and the “European Association of Nuclear Medicine Congress (EANM)”. We have determined in each abstract, which radionuclide was used. The most cited radionuclides in the SNM meeting were Tc‐99m (25.38%), F‐18 (18.93%), C‐11 (4.68%), I‐123 (4.57%), In‐111 (3.75%) and Tl‐201 (2.69%) and in the EANM congress were Tc‐99m (33.94%), F‐18 (11.88%), In‐111 (5.65%), I‐123 (5.50%), Tl‐201 (4.22%) and C‐11 (1.98%). The results indicate, that, although, the Tc‐99m is still the most cited radionuclide, there is an important citation of F‐18 in the abstracts presented in these two meetings. We can suggest that the status of the PET procedures is growing in the world.

Anatomy of a meta-analysis: A critical review of “Exercise echocardiography or exercise SPECT imaging? A meta-analysis of diagnostic test performance”

Background. Accurate diagnosis of coronary heart disease has the potential to contribute substantially to cost-effective delivery of health services. Recent work by Fleischmann et al (JAMA 1998;280:913-20) represents an effort to summarize the accuracy of exercise echocardiography and exercise single photon emission computed tomography (SPECT). Methods and Results. A critique of the previous work was constructed, obtaining the 44 articles used. These articles were reviewed and summarized with established techniques for meta-analysis. The studies summarized by Fleischmann et al were found to be significantly heterogeneous (echocardiography and SPECT, bothP < .001). In the SPECT cohort, combination of different radioisotopes and reading techniques, and inclusion of reports using experimental techniques, were sources of heterogeneity. In the echocardiography cohort, experimental techniques and an individual series were identified. When the sample was stratified for sources of heterogeneity, it was found that there was no significant difference in diagnostic accuracy between the echocardiography and SPECT techniques used in current clinical practice. Meta-regression with summary receiver operating characteristic curve techniques, after adjustment of the model for multicolinearity and outliers, revealed that there were no significant differences between SPECT as used in current clinical practice and echocardiography. Conclusion. The report by Fleischmann et al contains serious flaws that limit its validity and generalizability. (J Nucl Cardiol 2000;7:599-615.)

Rotating slant-hole single-photon emission-computed tomography

This dissertation presents a detailed investigation of the use of rotating slant-hole (RSH) collimators in single-photon emission-computed tomography(SPECT). We propose RSH SPECT as an alternative imaging technique, which may have advantages over more traditional SPECT techniques, in certain imaging applications. The basic imaging properties of RSH collimators are derived. This includes the derivation of expressions for the size and location of the common volume of view and the geometric resolution and efficiency. In addition, we derive an analytical expression for the geometric response and transfer functions of RSH collimators. The theoretical expressions for the aforementioned imaging characteristics are verified via Monte Carlo simulations and phantom experiments. Next, we present the development of a three-dimensional (3-D) analytic reconstruction algorithm for RSH SPECT. This includes the derivation of both a backprojection of the filtered projections and a filtering of the simple backprojections (BpjF) algorithm. The relationship between the derived 3-D RSH reconstruction filter and a number of other reconstruction filters is discussed. In addition, the implementation of the BpjF reconstruction algorithm is described and its performance is demonstrated via simulations and phantom experiments. We have also implemented an iterative ordered-subsets expectation-maximization (OS-EM) reconstruction algorithm for RSH SPECT. A detailed description of the development of the projector/backprojector employed by the OS-EM algorithm is provided. Simulation and phantom experiments are again used to demonstrate the performance of the projector/backprojector and the iterative OS-EM reconstruction algorithm. Rotating slant-hole SPECT has potential applications in cardiac and breast imaging. Thus, we demonstrate the feasibility, advantages, and disadvantages of using RSH SPECT via a comparison with conventional SPECT in a cardiac and breast imaging phantom experiment. In conclusion, we summarize the results presented and discuss their implications on the current and future state of RSH SPECT research.

The stability analysis of dynamic SPECT systems

SPECT (Single Photon Emission Computed Tomography) techniques have been applied to a wide range of medical studies. The stability of a SPECT model depends strongly upon the data collected. We show that a SPECT model is full rank and well-conditioned (stable) if the projection data are large enough. Condition number estimates for a linear model are given. Numerical results for a class of linear models confirm our theoretical analysis.