Instrumentation and computers for brain single photon emission computed tomography

Cerebral single-photon emission computed tomography (SPECT) requires attention to the instrumentation because of the anatomical location of the head at one end of the body, with a generally narrower diameter than the rest of the body. For a number of years, there have been SPECT units designed especially for head work, as well as general-purpose units that have performed well in imaging the head. The current emphasis on cerebral perfusion, using either agents that wash in and out with blood flow or agents that reflect blood flow in their static distribution, has allowed a concentration on imaging hardware and computer hardware and software for this purpose.     

Clinical evaluation of single photon emission computed tomography of the brain

Single photon emission computed tomography (ECT) was performed on 67 patients. ECT images were taken with a Shimadzu scintillation camera, LFOV-E, before a delayed scan.Eighteen of 67 patients showed abnormal findings on the ECT images. Fourteen of the 18 had a transmission X-ray CT (TCT) study as well. There were eleven cases with brain metastases, one case each of an old infarction, a skull metastasis, and a surgical wound. Eleven of fortynine ECT-negative patients had a TCT study as well, and intracranial lesions were found in five. The smallest lesion found by ECT was 0.5 cm in diameter on the TCT image and the largest lesion missed by ECT was a tumor in the corpus callosum, measuring 4.2×2.7 cm.As far as the patients who also received TCT study are concerned, both the ECT and the ordinary scan were thought to be equal in sixteen patients and ECT to be superior in seven whereas the ordinary scintigram was superior in two. At present, ECT is considered to be useful when it is used in addition to the ordinary scans.In the field of clinical nuclear medicine, the development of new radiopharmaceuticals which are labeled with single photon emitters and which can show the metabolic activity of the brain is eagerly awaited.     

Clinical evaluation of single photon emission computed tomography of the brain

Single photon emission computed tomography (ECT) was performed on 67 patients. ECT images were taken with a Shimadzu scintillation camera, LFOV-E, before a delayed scan. Eighteen of 67 patients showed abnormal findings on the ECT images. Fourteen of the 18 had a transmission X-ray CT (TCT) study as well. There were eleven cases with brain metastasis, and a surgical wound. Eleven of forty-nine ECT-negative patients had a TCT study as well, and intracranial lesions were found in five. The smallest lesion found by ECT was 0.5 cm in diameter on the TCT image and the largest lesion missed by ECT was a tumor in the corpus callosum, measuring 4.2 X 2.7 cm. As far as the patients who also received TCT study are concerned, both the ECT and the ordinary scan were thought to be equal in sixteen patients and ECT to be superior in seven whereas the ordinary scintigram was superior in two. At present, ECT is considered to be useful when it is used in addition to the ordinary scans. In the field of clinical nuclear medicine, the development of new radiopharmaceuticals which are labeled with single photon emitters and which can show the metabolic activity of the brain is eagerly awaited.     

Brain single photon emission computed tomography in neonates

This study was designed to rate the clinical value of [123I]iodoamphetamine (IMP) or [99mTc] hexamethyl propylene amine oxyme (HM-PAO) brain single photon emission computed tomography (SPECT) in neonates, especially in those likely to develop cerebral palsy. The results showed that SPECT abnormalities were congruent in most cases with structural lesions demonstrated by ultrasonography. However, mild bilateral ventricular dilatation and bilateral subependymal porencephalic cysts diagnosed by ultrasound were not associated with an abnormal SPECT finding. In contrast, some cortical periventricular and sylvian lesions and all the parasagittal lesions well visualized in SPECT studies were not diagnosed by ultrasound scans. In neonates with subependymal and/or intraventricular hemorrhage the existence of a parenchymal abnormality was only diagnosed by SPECT. These results indicate that [123I]IMP or [99mTc]HM-PAO brain SPECT shows a potential clinical value as the neurodevelopmental outcome is clearly related to the site, the extent, and the number of cerebral lesions. Long-term clinical follow-up is, however, mandatory in order to define which SPECT abnormality is associated with neurologic deficit.     

Positron emission tomography and single photon emission computed tomography in epilepsy care

Radiopharmaceutical brain imaging is clinically applied in planning resective epilepsy surgery. Cerebral sites of seizure generation-propagation are highly associated with regions of hyperperfusion during seizures, and with glucose hypometabolism interictally. For surgical planning in epilepsy, the functional imaging modalities currently established are ictal single photon emission computed tomography (SPECT) with [(99m)Tc]technetium-hexamethylpropyleneamine oxime (HMPAO) or with [(99m)Tc]technetium-ethylene cysteine dimer (ECD), and interictal positron emission tomography (PET) with 2-[(18)F]fluoro-2-deoxyglucose (FDG). Ictal SPECT and interictal FDG PET can be used in presurgical epilepsy evaluations to reliably: (1) determine the side of anterior temporal lobectomy, and in children the area of multilobar resection, without intracranial electroencephalographic recording of seizures; (2) select high-probability sites of intracranial electrode placement for recording ictal onsets; and, (3) determine the prognosis for complete seizure control following anterior temporal lobe resection. Coregistration of a patient's structural (magnetic resonance) and functional images, and statistical comparison of a patient's data with a normal data set, can increase the sensitivity and specificity of these SPECT and PET applications to the presurgical evaluation.     

Current and future radiopharmaceuticals for brain imaging with single photon emission computed tomography

Development of radiopharmaceuticals for functional brain imaging has progressed rapidly in recent years. Measurement of regional cerebral blood flow in humans can be achieved by using [123I]-iodoamphetamine or [99mTc]-HMPAO. Several other lipid-soluble [99mTc]-technetium complexes are currently undergoing clinical trials. New 123I-labeled agents designed to measure central nervous system receptors, including D1 and D2 dopamine, serotonin, muscarinic, and benzodiazepine receptors, have been developed. In conjunction with single photon emission computed tomography, they may provide useful tools to evaluate brain function related to changes in receptor concentration.     

Time sequential single photon emission computed tomography studies in brain tumour using thallium-201

Time sequential single photon emission computed tomography (SPECT) studies using thallium-201 were performed in 25 patients with brain tumours to evaluate the kinetics of thallium in the tumour and the biological malignancy grade preoperatively. After acquisition and reconstruction of SPECT data from 1 min post injection to 48 h (1, 2, 3, 4, 5, 6, 7, 8, 9, 10 and 15–20 min, followed by 4–6, 24 and 48 h), the thallium uptake ratio in the tumour versus the homologous contralateral area of the brain was calculated and compared with findings of X-ray CT, magnetic resonance imaging, cerebral angiography and histological investigations. Early uptake of thallium in tumours was related to tumour vascularity and the disruption of the blood-brain barrier. High and rapid uptake and slow reduction of thallium indicated a hypervascular malignant tumour; however, high and rapid uptake but rapid reduction of thallium indicated a hypervascular benign tumour, such as meningioma. Hypovascular and benign tumours tended to show low uptake and slow reduction of thallium. Long-lasting retention or uptake of thallium indicates tumour malignancy. Correspondence to: T. Ueda     

Single photon emission computed tomography imaging of brain tumors

Five radiotracers may be used for single-photon emission computed tomography (SPECT) imaging of brain tumors, namely technetium 99m pertechnetate, iodine-123 amphetamine derivatives, 99mTc-hexamethyl propylene amine oxime (HMPAO), thallium 201, and 123I alpha methyl tyrosine. Of these, pertechnetate may be considered as an "historical" procedure in brain tumors. However, there may be some equivocal cases in computed tomography or magnetic resonance imaging, where this procedure may still be used. In 1981, 123I isopropyl amphetamine was first used in brain tumors. Further studies showed, however, that IMP is not a useful tool for brain imaging in tumorous lesions. In 1986, 99mTc HMPAO appeared on the European market as a new tumor imaging agent. Some useful clinical results were obtained in patients before and after chemotherapy or radiotherapy. Thallium-201 was incidentally noted to accumulate in tumors. Using a threshold index, this agent can be used to distinguish low-versus high-grade lesions. The most promising agent for brain tumor SPECT is 123I-alpha methyl tyrosine, which shows potential to evaluate therapeutic procedures in brain tumors and may improve the differentiation between abscess and glioblastoma. The most promising aspect is the differentiation of tumor recurrences and scar tissue after brain surgery.     

The use of single photon emission computed tomography in depressive disorders

Single photon emission computed tomography (SPECT) and positron emission tomography (PET) have advanced our understanding of the biological underpinnings of depression. There is, however, considerable variability in the literature. Depression is a complex disorder with marked heterogeneity in diagnosis and treatment. There is also evidence of heterogeneity in pathophysiology. In addition, the literature is marked by inconsistencies in the use of imaging techniques and data-analytical procedures. In this review we have attempted to focus on the SPECT studies that have used more refined methodologies and more homogenous clinical sub-groups of patients. We have focused on the main diagnostic sub-types of depression and on specific issues such as treatment response, correlates of neuroimaging abnormalities in depression, and so-called 'emotional circuitry' - the connectivity of regions implicated in depression. The future of molecular imaging in depression will be determined by the pace of the development of useful ligands and the exciting opportunities emerging in the field of imaging genomics. Future studies must attend to several key confounds including clinical heterogeneity, medication and the problems surrounding recruitment of drug-naive patients. It remains the case that longitudinal studies are the design of choice if questions relating to state and trait are to be addressed. Molecular imaging will be used increasingly to quantify neuroreceptor and transporter binding, and the activity of neurtransmitters, allowing the neurochemistry of this complex condition to be explored.     

The role of single photon emission computed tomography in bone imaging

Single photon emission computed tomography (SPECT) of the bone is the second most frequently performed SPECT examination in routine nuclear medicine practice, with cardiac SPECT being the most frequent. Compared with planar scintigraphy, SPECT increases image contrast and improves lesion detection and localization. Studies have documented the unique diagnostic information provided by SPECT, particularly for avascular necrosis of the femoral head, in patients with back pain, for the differential diagnosis between malignant and benign spinal lesions, in the detection of metastatic cancer in the spine, for the diagnosis of temporomandibular joint internal derangement, and for the evaluation of acute and chronic knee pain. Although less rigorously documented, SPECT is being increasingly used in all types of situations that demand more precise anatomic localization of abnormal tracer uptake. The effectiveness of bone SPECT increases with the selection of the proper collimator, which allows one to acquire adequate counts and minimize the patient-to-detector distance. Low-energy, ultrahigh-resolution or high-resolution collimation is preferred over all-purpose collimators. Multihead gamma cameras can increase the counts obtained or shorten acquisition time, making SPECT acquisitions more practical in busy departments and also increasing image quality compared with single-head cameras. Iterative reconstruction, with the use of ordered subsets estimation maximization, provides better quality images than classical filtered back projection algorithms. Three-dimensional image analysis often aids lesion localization.     

The role of single photon emission computed tomography in bone scintigraphy

The increasing availability for routine nuclear medicine studies of single photon emission computed tomography (SPECT) reflects the realisation of its ability to improve lesional detection and the assessment of location. This is achieved by removing unwanted surrounding radioactivity and thus delineating with greater clarity deeper areas of preferential accumulation. By removing the superimposition of structures, SPECT offers considerable potential for improved diagnostic accuracy in suspected bone and joint disease. Time and cost, however, necessitate a selective use of the technique. The maximum advantages arise from studies of the head, spine, skull and knees. The role of SPECT does, in some instances, lie in providing increased sensitivity in the detection of focal uptake while in others it complements alternative imaging modalities by identifying the functional status of an abnormality and thus may demonstrate its clinical significance. Since such information may be obtained by planar scintigraphy using techniques such as pinhole collimation, continuing evaluation is essential to ascertain the precise indications for SPECT imaging.Based on a presentation at the 15th Annual Meeting of the International Skeletal Society, Sydney, Australia, September 1988     

Single photon emission computed tomography and statistical parametric mapping analysis in cirrhotic patients with and without minimal hepatic encephalopathy

OBJECTIVE: The early diagnosis and treatment of cognitive impairment in cirrhotic patients is needed to improve the patients' daily living. In this study, alterations of regional cerebral blood flow (rCBF) were evaluated in cirrhotic patients using statistical parametric mapping (SPM). The relationships between rCBF and neuropsychological test, severity of disease and biochemical data were also assessed. METHODS: 99mTc-ethyl cysteinate dimer single photon emission computed tomography was performed in 20 patients with non-alcoholic liver cirrhosis without overt hepatic encephalopathy (HE) and in 20 age-matched healthy subjects. Neuropsychological tests were performed in 16 patients; of these 7 had minimal HE. Regional CBF images were also analyzed in these groups using SPM. RESULTS: On SPM analysis, cirrhotic patients showed regions of significant hypoperfusion in the superior and middle frontal gyri, and inferior parietal lobules compared with the control group. These areas included parts of the premotor and parietal associated areas of the cortex. Among the cirrhotic patients, those with minimal HE had regions of significant hypoperfusion in the cingulate gyri bilaterally as compared with those without minimal HE. CONCLUSIONS: Abnormal function in the above regions may account for the relatively selective neuropsychological deficits in the cognitive status of patients with cirrhosis. These findings may be important in the identification and management of cirrhotic patients with minimal HE.     

Three-dimensional display of data obtained by single photon emission computed tomography

Three-dimensional display of radioactive distributions has been achieved using data generated by single photon emission computed tomography (SPECT). Computer techniques for constructing images are presented and the special problems associated with manipulating SPECT data are reviewed. The potential role of three-dimensional imaging in nuclear medicine is discussed and SPECT studies from several illustrative cases are presented.     

Retrospective evaluation of single photon emission computed tomography of the liver

Retrospective analysis, including indications for examination, of 335 consecutive liver examinations of adults with single photon emission computed tomography performed at the Karolinska Hospital during the first eight months of 1981 has been carried out. 85.1% of the investigations were performed in tumour patients. This group underwent retrospective evaluation specifically regarding space occupying lesions of the liver with a minimum follow-up time of 3 years. An adequate follow-up of 87.4% was achieved. The study showed a sensitivity of 82.7% and a specificity of 93.9%. The positive and negative predictive values were 78.2% and 95.4%, respectively. 4.4% of the examinations were regarded as equivocal. Compared to previously reported values for planar liver scintigraphy derived from several different studies, the tomographic technique produced no increase of specificity or positive predictive value but a higher total accuracy, probably due to better clarification of the hepatic anatomy. The false positive, false negative and equivocal diagnoses were analysed and reported.     

Retrospective evaluation of single photon emission computed tomography of the liver

Retrospective analysis, including indications for examination, of 335 consecutive liver examinations of adults with single photon emission computed tomography performed at the Karolinska Hospital during the first eight months of 1981 has been carried out. 85.1% of the investigations were performed in tumour patients. This group underwent retrospective evaluation specifically regarding space occupying lesions of the liver with a minimum followup time of 3 years. An adequate follow-up of 87.4% was achieved. The study showed a sensitivity of 82.7% and a specificity of 93.9%. The positive and negative predictive values were 78.2% and 95.4%, respectively. 4.4% of the examinations were regarded as equivocal. Compared to previously reported values for planar liver scintigraphy derived from several different studies, the tomographic technique produced no increase of specificity or positive predictive value but a higher total accuracy, probably due to better clarification of the hepatic anatomy. The false positive, false negative and equivocal diagnoses were analysed and reported.