Single photon emission computerized tomography (SPECT) for estimates of liver and spleen volume

A simple procedure is described for estimates of liver and spleen volume using the imaging data obtained during single photon emission computerized tomography ( SPECT ). In vitro studies were carried out to obtain correlation and regression coefficients for volume estimations. Using these regression coefficients, we estimated liver and spleen volumes in 50 patients. Phantom and organ volumes were also calculated from transmission computed tomography (TCT), whose results served as the reference procedure against which SPECT -determined volumes were compared. The influence of radiotracer uptake on scintigraphic volume predictions was also assessed. For the in vitro measurements, SPECT volumes predicted the true volumes with a coefficient of correlation of 0.997. When in vivo SPECT volumes were correlated with those obtained by TCT, a coefficient in excess of 0.9 was achieved. SPECT volume determinations proved to be influenced by organ uptake of tracer; high liver uptake and low spleen-to-liver ratios gave the best results. It is concluded that SPECT imaging offers access to rapid and exact volume estimation.     

Brain SPECT imaging and whole-body biodistribution with [(123)I]ADAM - a serotonin transporter radiotracer in healthy human subjects

INTRODUCTION: [(123)I]-2-((2-((dimethylamino)methyl)phenyl)thio)-5-iodophenylamine ([(123)I]ADAM), a novel radiotracer, has promising application in the imaging of the serotonin transporter (SERT) in the human brain. In this study, the optimal scanning time for acquiring brain single photon emission computed tomography (SPECT) images was determined by performing dynamic SPECT studies at intervals from 0 to 6 h postinjection of [(123)I]ADAM. Additionally, radiation-absorbed doses were determined for three healthy human subjects using attenuation-corrected images. METHODS: Twelve subjects were randomized into one of three study groups as follows: whole-body distribution imaging (n=3), dynamic SPECT imaging (n=3) and brain SPECT imaging (n=6). The radiation-absorbed dose was calculated using MIRDOSE 3.0 software with attenuation-corrected data. The specific binding (SB) ratio of the brain stem was measured from dynamic SPECT images to determine the optimal scanning time. RESULTS: Dynamic SPECT images showed that the SB of the brain stem gradually increased to a maximum 4 h postinjection. Single photon emission computed tomography images at 4 h postinjection showed a high uptake of the radiotracer (SB) in the hypothalamus (1.40+/-0.12), brain stem (1.44+/-0.16), pons (1.13+/-0.14) and medial temporal lobe (0.59+/-0.10). The mean adult male value of effective dose was 3.37 x 10(-2) mSv/MBq with a 4.8-h urine-voiding interval. Initial high uptake in SERT-rich sites was demonstrated in the lung and brain. A prominent washout of the radiotracer from the lung further increased brain radioactivity that reached a peak value of 5.03% of injected dose 40 min postinjection. CONCLUSIONS: [(123)I]ADAM is a promising radiotracer for SPECT imaging of SERT in humans with acceptable dosimetry and high uptake in SERT-rich regions. Brain SPECT images taken within 4 h following injection show optimal levels of radiotracer uptake in known SERT sites. However, dynamic changes in lung SERT distribution must be carefully evaluated.     

An elliptical SPECT system with slit-slat collimation for cardiac imaging

Cardiac studies are a good candidate for SPECT (single photon emission computed tomography) because of the large clinical demand and the need for improved image quality. But SPECT imaging suffers from poor spatial resolution and high statistical noise. A new SPECT system with slit-slat collimation arranged on an elliptical arc for cardiac imaging is proposed in this paper. Simulated emission computed tomography data are generated along an elliptical moving orbit with system configuration parameters. The iterative reconstruction techniques are used to implement the cardiac imaging of the proposed SPECT system. Image reconstruction can be done using the OS-EM algorithm from the data collected. This system is developed to improve the reconstructed image if attenuation correction and depth-dependent correction are included in the reconstruction, and the body contour is used in the reconstruction for severely truncated data. The simulation results show that the present methods can provide significant improvement in the spatial resolution and the image quality of SPECT sets.     

Positron emission tomography and single-photon emission computed tomography in substance abuse research

Many advances in the conceptualization of addiction as a disease of the brain have come from the application of imaging technologies directly in the human drug abuser. New knowledge has been driven by advances in radiotracer design and chemistry and positron emission tomography (PET) and single-photon emission computed tomography (SPECT) instrumentation and the integration of these scientific tools with the tools of biochemistry, pharmacology, and medicine. This topic cuts across the medical specialties of neurology, psychiatry, oncology, and cardiology because of the high medical, social, and economic toll that drugs of abuse, including the legal drugs, cigarettes and alcohol, take on society. This article highlights recent advances in the use of PET and SPECT imaging to measure the pharmacokinetic and pharmacodynamic effects of drugs of abuse on the human brain.     

Automated radiosynthesis of the Pittsburg compound-B using a commercial synthesizer

BACKGROUND: The Pittsburgh compound-B ([C]PIB) is a highly interesting radiotracer for imaging amyloid plaques in Alzheimer's disease by positron emission tomography (PET). An increasing number of PET centres schedule its transfer for clinical studies and therefore are interested in its automated synthesis. METHOD: With the aim of flexibility, we reported the first fully automated synthesis of [C]PIB with the coupling of two commercial synthesizers. RESULTS: [C]PIB was prepared from 2-(4'-aminophenyl)-6-hydroxybenzothiazole by [C]methyl triflate methylation reacting in an high-performance liquid chromatography loop and resulting in a total radiochemical yield of 13+/-15% after a synthesis time of 25 min. The specific activity of [C]PIB was 20-60 GBq/mumol and its radiochemical purity is more than 99%. CONCLUSION: The rapid synthesis and the automatic auto-cleaning procedure allow convenient and reproducible [C]PIB synthesis to be performed during the same day for preclinical or clinical PET scans.     

Improvement in PET myocardial perfusion image quality and quantification with flurpiridaz F 18

Rubidium-82 (⁸²Rb), the currently commercially available radiotracer for positron emission tomography (PET) myocardial perfusion imaging (MPI), has led to wide availability of PET-MPI for stress-rest imaging. Compared to SPECT MPI, myocardial perfusion PET images have higher spatial and contrast resolution, are less affected by radiotracer scatter, benefit from more precise attenuation correction, and allow dynamic first pass imaging. In addition, PET imaging allows assessment of myocardial function at peak stress and measurement of absolute myocardial blood flow, thus providing critical data not available with SPECT imaging. Further enhancements of the high quality of PET perfusion images may be realized by technologies under development such as respiratory gating, combined respiratory, and ECG gating to generate “motion-frozen” cardiac images, automated patient motion correction software, and high-definition PET, which reduces distortions introduced by the circular geometry of the scanner. Early studies indicate that the experimental PET radiopharmaceutical flurpiridaz F 18 provides high-quality, high-resolution myocardial perfusion images that may enable improved clinical MPI, and has properties well suited to optimized performance by application of these quantitative analytic technologies.     

First ex vivo study demonstrating that <Superscript>99m</Superscript>Tc-NTP 15-5 radiotracer binds to human articular cartilage

Purpose  

Preclinical data pointed to ^99mTc-NTP 15-5 as a good candidate for single photon emission computed tomography (SPECT) imaging of cartilaginous disease. We set out to investigate and quantify ^99mTc-NTP 15-5 ex vivo uptake by human articular cartilage relative to bone ^99mTc-hydroxymethylene diphosphonate (HMDP) radiotracer.     

Brain radioligands--state of the art and new trends.

Non-invasive radioligand imaging methods for brain receptor studies use either short-lived positron-emitting radionuclides such as 11C and 18F for positron emission tomography (PET) or single photon-emitting radionuclides such as 123I for single photon emission computed tomography (SPECT). PET and SPECT use radioligands which are injected intravenously into experimental animals, human volunteers or patients. The main applications of radioligands in brain research concern human neuropsychopharmacology and the discovery and development of novel drugs to be used in thetherapy of neurological and psychiatric disorders. A basic problem in PET and SPECT brain receptor studies is the lack of useful radioligands with appropriate binding characteristics. Prerequisite criteria need to be satisfied for a radioligand to reveal target binding sites in vivo. This section will discuss these important criteria and also review recent examples in neuroreceptor radioligand development such as selective radioligands for brain monoamine transporters.     

Validation of 8-[123I]iodo-L-1,2,3,4-tetrahydro-7-hydroxyisoquinoline-3-carboxylic acid as an imaging agent for prostate cancer in experimental models of human prostate cancer

INTRODUCTION: Very few tracers are currently available for the detection and staging of prostate cancer with positron emission tomography and single-photon emission computed tomography. This study evaluates the potential of 8-[123I]iodo-1,2,3,4-tetrahydro-7-hydroxyisoquinoline-3-carboxylic acid [ITIC(OH)] as an imaging agent for prostate cancer in experimental models of human prostate cancer. METHODS: ITIC(OH) was prepared by the IODO-GEN method, with 82+/-7% radiochemical yield and >99% radiochemical purity after high-performance liquid chromatography. Thereafter, ITIC(OH) was examined in CD-1 nu/nu mice engrafted with human PC-3 and DU-145 prostate cancer in the flank or orthotopically in the prostate. Bioevaluation involved examination of the in vivo stability and uptake characteristics of ITIC(OH) into tumors and different organs by dynamic in vivo analysis and gamma counting of organs of interest after dissection. RESULTS: ITIC(OH) showed good in vivo stability for biological investigations and was primary cleared through urine. In vivo, ITIC(OH) accumulated highly and specifically in tumors, reaching 13.6+/-2.1% to 16.2+/-2.5% injected dose per gram (ID/g) in heterotopic tumors compared with 14.8+/-2.6% and 17.6+/-3.4% ID/g in orthotopic tumor engrafts at 60 and 240 min postinjection, respectively. In contrast, radioactivity uptake in the blood, spleen, liver and gastrointestinal tract was moderate and decreased with time, resulting in marked tumor-to-background and excellent visualization of tumors. CONCLUSION: These results suggest that ITIC(OH) is a promising candidate as radiotracer for detecting prostate cancer and warrants further studies in patients to ascertain its potential as an imaging agent for clinical use.     

Synthesis of [123I]IBZM: a reliable procedure for routine clinical studies

The single photon emission computed tomography (SPECT) D2/D3 receptor radiotracer [123I]IBZM, is prepared by electrophilic radioiodination of the precursor BZM with high-purity sodium [123I]iodide in the presence of diluted peracetic acid. However, in our hands, the most commonly used procedure for this radiosynthesis produced variable and inconsistent labeling yields, to such extent that it became inappropriate for routine clinical studies. Our goal was to modify the labeling procedure, to obtain consistently better labeling and radiochemical yields. The best conditions found for the radioiodination were as follows: 50 microg precursor in 50 microL EtOH mixed with buffer pH 2; Na[123I]I in 0.1 M NaOH (< 180 microL), 50 microL peracetic acid diluted solution, heating at 65 degrees C for 14 min. Purification was achieved by solid phase extraction (SPE) and reverse-phase high performance liquid chromatography (HPLC). Under these conditions, labeling yield average was 76 +/- 4% (n = 31); radiochemical yield was 69 +/- 4% and radiochemical purity was 98 +/- 1%. With larger volumes of the Na[123I]I solution the yields were consistent but lower. For example, for volumes between 417 and 523 microL the labeling yield was 61 +/- 5% (n = 21), radiochemical yield was 56 +/- 5% and radiochemical purity was 98 +/- 1%.     

Role of fusion in radiotherapy treatment planning

The fusion of functional imaging to traditional imaging modalities, such as computed tomography (CT) and magnetic resonance imaging (MRI), is currently being investigated in radiotherapy treatment planning. Most studies that have been reported are in patients with lung, brain, or head and neck neoplasms. There is a potential role for either positron emission tomography (PET) or single photon emission computed tomography (SPECT) to delineate biologically active or tumor-bearing areas that otherwise would not be detected by CT or MRI. Furthermore, target volumes may be modified by using functional imaging, which can have a significant impact in the modern era of three-dimensional radiotherapy. SPECT may also be able to identify "nonfunctional" surrounding tissue and may influence radiotherapy beam arrangement.     

Abdominal SPECT imaging

Over the past several years, abdominal single photon emission computed tomography (SPECT) imaging has evolved from a research tool to an important clinical imaging modality that is helpful in the diagnostic assessment of a wide variety of disorders involving the abdominal viscera. Although liver-spleen imaging is the most popular of the abdominal SPECT procedures, blood pool imaging is becoming much more widely utilized for the evaluation of cavernous hemangiomas of the liver as well as other vascular abnormalities in the abdomen. Adjunctive indium leukocyte and gallium SPECT studies are also proving to be of value in the assessment of a variety of infectious and neoplastic diseases. As more experience is acquired in this area, SPECT should become the primary imaging modality for both gallium and indium white blood cells in many institutions. Renal SPECT, on the other hand, has only recently been used as a clinical imaging modality for the assessment of such parameters as renal depth and volume. The exact role of renal SPECT as a clinical tool is, therefore, yet to be determined.     

Synergistic value of single-photon emission computed tomography/computed tomography fusion to radioimmunoscintigraphic imaging of prostate cancer

The rationale on which positron emission tomography/computed tomography (PET/CT) imaging is based, combining the functional features of PET with the anatomic detail of CT, provides many advantages that are easily transferable to single-photon emission computed tomography (SPECT)/CT imaging. Our efforts have focused on applying fused SPECT/CT imaging to identify prostate cancer and its metastasis and recurrence through radioimmunoscintigraphy (RIS). This application of RIS to imaging prostate cancer requires 2 key components: (1) a well-defined target associated with the cancer and (2) a "magic bullet" to seek that target. A well-characterized RIS target for prostate cancer is prostate-specific membrane antigen, or PSMA, and finding the bullet to seek this target with high sensitivity and specificity has been the focus of intensive study for nearly two decades. One of the candidate bullets developed is capromab pendetide, which is a monoclonal antibody that seeks PSMA. This antibody is commercially available as ProstaScint, which can be labeled with indium-111 to localize prostate cancer via SPECT imaging. In the course of applying fused SPECT/CT ProstaScint imaging to more than 800 prostate cancer cases, numerous refinements to our protocol have evolved that are aimed at staging the cancer with utmost accuracy. In addition to optimizing the localization of prostate cancer and its metastasis, these refinements also have been extended toward guiding both the implantation of radioactive seeds in brachytherapy and in other types of radiation therapy which is illustrated through 5 case reports. Progress in the therapeutic targeting of PSMA is also being actively explored, which has more universal ramifications because PSMA is found in the neovasculature of other types of cancers.     

Renal single photon emission computed tomography: should we do it?

Although single photon emission computed tomography (SPECT) imaging has established a place for itself in clinical nuclear medicine for heart and brain studies, its place in renal imaging is not yet clear. Renal SPECT has been subject to limitations imposed by the efficiency of imaging equipment, and has been confined to use with static imaging agents such as technetium-99m (99mTc) dimercaptosuccinate (DMSA). SPECT has been used to investigate space-occupying lesions and anatomical abnormalities, and for quantitative studies of renal uptake and volume. In these areas, it has provided little advantage over conventional imaging, but it has been helpful in individual cases. High-resolution SPECT is a promising new development, which may have applications in detecting and classifying renal scarring. It deserves careful evaluation.     

Adrenal gland scintigraphy

There is no question that high-resolution imaging techniques have revolutionized the approach to diagnostic imaging. Computed tomography (CT) and magnetic resonance imaging provide exquisite images of the adrenal glands and offer the best initial imaging approach in the evaluation of patients with suspected adrenal disease. However, an assessment of anatomy is only a portion of the diagnostic effort, which begins with a biochemical evaluation to establish the presence of adrenal gland dysfunction. With a confirmed biochemical diagnosis in hand, a logical and stepwise diagnostic approach can be tailored to a particular patient. Where scintigraphy fits in the evaluation of diseases of the adrenal cortex and medulla in the context of high-resolution imaging and which radiopharmaceuticals should be deployed has changed substantially during the last 2 decades. Adrenal functional imaging has evolved from classic planar scintigraphy to single-photon emission computed tomography (SPECT) and positron emission tomography (PET) using tracers that, by targeting specific metabolic or synthetic processes within the gland, have depicted adrenal pathophysiology. New PET/CT and SPECT/CT technologies integrate anatomic and functional information and redefine the radiotracer principle in the larger context of high resolution anatomic imaging.     

V/Q imaging in 2010: a quick start guide

In this article we review protocols for ventilation-perfusion (V/Q) imaging with current generation technology. Although many groups have expressed interest in moving from planar lung V/Q imaging to single-photon emission computed tomography (SPECT) methods, few resources or guidelines exist for suggested protocols. Here, we provide an introduction to help establish protocols for planar and SPECT V/Q imaging and display that should be readily transferable into a clinical department's routine practice. We emphasize, in particular, the need for a good ventilation study and that acquiring planar images as well as SPECT can be negated by producing acceptable planar-like images from the SPECT data.     

Molecular imaging of hypoxia with radiolabelled agents

Tissue hypoxia results from an inadequate supply of oxygen (O₂) that compromises biological functions. Structural and functional abnormalities of the tumour vasculature together with altered diffusion conditions inside the tumour seem to be the main causes of tumour hypoxia. Evidence from experimental and clinical studies points to a role for tumour hypoxia in tumour propagation, resistance to therapy and malignant progression. This has led to the development of assays for the detection of hypoxia in patients in order to predict outcome and identify patients with a worse prognosis and/or patients that would benefit from appropriate treatments. A variety of invasive and non-invasive approaches have been developed to measure tumour oxygenation including oxygen-sensitive electrodes and hypoxia marker techniques using various labels that can be detected by different methods such as positron emission tomography (PET), single photon emission computed tomography (SPECT), magnetic resonance imaging (MRI), autoradiography and immunohistochemistry. This review aims to give a detailed overview of non-invasive molecular imaging modalities with radiolabelled PET and SPECT tracers that are available to measure tumour hypoxia.     

The hazards of lack of co-registration of ictal brain SPECT with MRI: A case report of sinusitis mimicking a brainstem seizure focus

BACKGROUND: Single photon emission computed tomography (SPECT) following injection of radiotracer during a seizure is known as ictal SPECT. Comparison of an ictal SPECT study to a baseline or interictal study can aid identification of a seizure focus. CASE PRESENTATION: A young woman with encephalitis and refractory seizures underwent brain SPECT during a period of frequent seizure-like episodes, and during a seizure-free period. A focal area of increased radiotracer uptake present only when she was experiencing frequent seizure-like episodes was originally localized to the brainstem, but with later computerized co-registration of SPECT to MRI, was found to lie outside the brain, in the region of the sphenoid sinus. CONCLUSION: Low-resolution SPECT images present difficulties in interpretation, which can be overcome through co-registration to higher-resolution structural images.     

Single-photon emission computed tomography/computed tomography in lung cancer and malignant lymphoma

In nuclear oncology, despite the fast-growing diffusion of (18)F-fluorodeoxyglucose positron emission tomography (FDG-PET), single-photon emission computed tomography (SPECT) studies can still play an useful clinical role in several applications. The main limitation of SPECT imaging with tumor-seeking agents is the lack of the structural delineation of the pathologic processes they detect; this drawback sometimes renders SPECT interpretation difficult and can diminish its diagnostic accuracy. Fusion with morphological studies can overcome this limitation by giving an anatomical map to scintigraphic data. In the past, software-based fusion of independently performed SPECT and CT images proved to be time-consuming and impractical for routine use. The recent development of dual-modality integrated imaging systems that provide functional (SPECT) and anatomical (CT) images in the same scanning session, with the acquired images coregistered by means of the hardware, has opened a new era in this field. The first reports indicate that SPECT/CT is very useful in cancer imaging because it is able to provide further information of clinical value in several cases. In SPECT, studies of lung cancer and malignant lymphomas using different radiopharmaceutical, hybrid images are of value in providing the correct localization of tumor sites, with a precise detection of the involved organs, and the definition of their functional status, and in allowing the exclusion of disease in sites of physiologic tracer uptake. Therefore, in lung cancer and lymphomas, hybrid SPECT/CT can play a role in the diagnosis of the primary tumor, in the staging of the disease, in the follow-up, in the monitoring of therapy, in the detection of recurrence, and in dosimetric estimations for target radionuclide therapy.     

The pinhole: gateway to ultra-high-resolution three-dimensional radionuclide imaging

Today the majority of clinical molecular imaging procedures are carried out with single-photon emitters and gamma cameras, in planar mode and single-photon emission computed tomography (SPECT) mode. Thanks to the development of advanced multi-pinhole collimation technologies, SPECT imaging of small experimental animals is rapidly gaining in popularity. Whereas resolutions in routine clinical SPECT are typically larger than 1 cm (corresponding to >1,000 μl), it has recently proved possible to obtain spatial resolutions of about 0.35 mm (≈0.04 μl) in the mouse. Meanwhile, SPECT systems that promise an even better performance are under construction. The new systems are able to monitor functions in even smaller structures of the mouse than was possible with dedicated small animal positron emission tomography (≈1 mm resolution, corresponding to 1 μl). This paper provides a brief history of image formation with pinholes and explains the principles of pinhole imaging and pinhole tomography and the basics of modern image reconstruction methods required for such systems. Some recently introduced ultra-high-resolution small animal SPECT instruments are discussed and new avenues for improving system performance are explored. This may lead to many completely new biomedical applications. We also demonstrate that clinical SPECT systems with focussing pinhole gamma cameras will be able to produce images with a resolution that may become superior to that of PET for major clinical applications. A design study of a cardiac pinhole SPECT system indicates that the heart can be imaged an order of magnitude faster or with much more detail than is possible with currently used parallel-hole SPECT (e.g. 3–4 mm instead of ≈8 mm system resolution).