Clinical brain imaging with isopropyl-iodoamphetamine and SPECT

Brain SPECT of Creutzfeldt-Jakob disease

SPECT imaging with I-123 IMP or Tc-99m HMPAO was performed in two patients with Creutzfeldt-Jakob disease to evaluate abnormalities in brain perfusion. In the first patient, there was decreased perfusion of the left frontal, parietal, and temporal lobes. CT and MRI were negative. In the second patient, there was patchy perfusion and slightly decreased perfusion of the right hemisphere. MRI revealed slight brain atrophy and bilateral high intensity areas in the basal ganglia on T2 weighted images. Subsequent SPECT imaging revealed severely decreased perfusion of the entire brain. Subsequent MRI demonstrated severe brain atrophy.

Combined study of 99mTc-HMPAO SPECT and computerized electroencephalographic topography (CET) in patients with medically refractory complex partial epilepsy

For successful surgery for drug-resistant epilepsy the site of the seizure focus needs to be known exactly. The purpose of this study was to compare the evaluation of the regional cerebral blood flow (rCBF) (localization and degree of disturbances) by 99mTc-hexamethylpropyleneamineoxime (HMPAO) single photon emission computed tomography (SPECT) with computerized electroencephalographic topography (CET) and transmission computed X-ray tomography (CT) in partial epilepsy. The study included 20 patients with medically refractory complex partial seizures. Of the 20 patients included, 15 were studied interictally, four ictally and one in both states, interictally and ictally. 99mTc-HMPAO SPECT detected rCBF changes in 95% of the patients. Interictal studies demonstrated focal areas of hypoperfusion in 93% of the patients. Ictal studies demonstrated an area of hyperperfusion in all patients. Blood flow disturbances in deeper structures of the brain, such as basal ganglia, could be detected. The areas of abnormal 99mTc-HMPAO uptake were concordant, in localization, with CET in 85% of the patients. Abnormal data with CT scans were found in only 45% of the patients. Focal lesions were found in 20% of the patients by CT scans. 99mTc-HMPAO SPECT combined with CET may be a useful screening procedure prior to referral for invasive diagnostic procedures in future management with medically refractory complex partial seizures.

Evaluation of cerebral vasospasm in patients with subarachnoid hemorrhage using single photon emission computed tomography

Cerebral vasospasm (CVS) occurs as a result of the breakdown in cerebral autoregulation mechanisms. Because cerebral vasospasm can occur after subarachnoid hemorrhage (SAH), it is important to evaluate borderline perfusion. Evaluation of borderline vascular insufficiency is important to reduce ischemic complications. In this study 25 patients with SAH were investigated by somatosensory evoked potentials (SEP), computed tomography (CT), digital subtraction angiography (DSA) and single photon emission computed tomography (SPECT) in order to predict borderline ischemic areas. Clinical grades were also correlated with these investigations. Thirteen patients had symptomatic vasospasm and 15 patients had angiographic vasospasm. SPECT showed hypoperfusion in 22 out of 25 patients. CT predicted CVS in 8 of these 22 patients. Our study shows that brain perfusion SPECT is a non-traumatic, non-invasive, non-allergic, inexpensive method for the prediction of cerebral vasospasm. We conclude that brain SPECT with Tc-99m HM-PAO is an accessible technique that can demonstrate varying degrees of regional tissue hypoperfusion in patients with delayed ischemic deficits due to CVS following SAH.

Speech fluency in aphasia. Regional cerebral blood flow correlates of recovery using single-photon emission computed tomography

This study investigated the relationship between diminished regional cerebral blood flow (rCBF) and the recovery of fluent speech in aphasia. Single-photon emission computed tomographic brain scans using [123I]N-isopropyl-p-iodoamphetamine were obtained from 14 nonfluent aphasic patients within 30 days of cerebral infarction. Measurements of speech fluency were acquired initially and at 3 months after infarction. Nearly all of the patients exhibited significant hypoperfusion to combinations of the anterior and posterior regions of the basal ganglion, the periventricular white matter, and the inferior frontal regions. Only the inferior frontal area was significantly associated with recovery of fluent speech. This region was hypoperfused in 4 of 5 patients with poor recovery while 8 of the 9 patients with good speech fluency recovery demonstrated normal rCBF to the inferior frontal region.

Utility of late N-isopropyl-p-(iodine-123)-iodoamphetamine brain distribution in predicting outcome following cerebral infarction

BACKGROUND AND PURPOSE

The purpose of this study was to determine utility of late N-isopropyl-p-(iodine-123)-iodoamphetamine distribution in predicting neurological and language outcome.

METHODS

We prospectively studied 29 patients with unilateral hemispheric ischemic cerebral infarction using the neuroimaging method of single-photon emission computed tomography and the above tracer. Four different imaging measures reflecting late tracer distribution or redistribution and three measures indicative of the patients' overall neurological or language outcome at 3 months were used in the data analysis. All patients had neuroimaging within 30 days of infarction, and 14 patients were imaged within 10 days of infarction. Data analysis was performed for all patients combined and then separately on the groups imaged within 10 days of and more than 10 days after infarction.

RESULTS

The volume of the late image defect significantly correlated with one measure of neurological outcome in the whole group and in those imaged more than 10 days after cerebral infarction. However, these results are difficult to explain based on the present understanding of the physiology of late N-isopropyl-p-(iodine-123)-iodoamphetamine distribution.

CONCLUSIONS

We feel that the pattern of late N-isopropyl-p-(iodine-123)-iodoamphetamine distribution is probably not useful as an independent predictor of neurological and language outcome.

Studies of central nervous system disorders with single photon emission computed tomography and positron emission tomography: evolution over the past 2 decades

Single photon emission computed tomography (SPECT) was introduced in the 1960s to detect breakdowns in the blood-brain barrier and was replaced by x-ray computed tomography in the mid-1970s. The development of the deoxyglucose (DG) technique to measure regional cerebral glucose metabolism by employing either autoradiography, using 14CDG, or positron emission tomography (PET), using 18FDG, added a major dimension to the investigation of brain function. In the late 1970s and early 1980s, the FDG-PET technique was widely used to examine a variety of neuropsychiatric disorders. It soon became apparent that functional imaging was more sensitive than anatomic imaging in detecting abnormalities of the brain related to aging, dementia, tumors, seizures, cerebral vascular accidents, and psychiatric problems. Because of its complexity and the cost involved, PET was used in a limited number of centers in the United States. However, the success of PET resulted in the resurgence of interest in SPECT as an alternative technology after almost a decade. This became possible because of the synthesis of iodine 123- and technetium 99m-labeled radiopharmaceuticals to determine regional cerebral blood flow. Since blood flow and metabolism are coupled in most pathological states, patterns of abnormality noted on SPECT were similar to those seen on PET in many disorders. Since the introduction of high resolution SPECT imaging instruments, the role of SPECT has been further enhanced. The successful synthesis of both positron and single emitting radioligands to image dopamine and other receptors has started a new era in neurosciences and will have a far-reaching impact on the day-to-day practice of neuropsychiatry.

In vitro covalent binding of new brain tracer, para-125I-amphetamine, to rat liver and lung microsomes

p-125I-amphetamine (I-Amp) is retained significantly in liver and lung during brain tomoscintigraphy. To attempt to explain this clinical observation, we have investigated the interaction of I-Amp with rat liver and lung microsomal proteins. Studies using spectral shift technique indicate that low concentration of I-Amp gives a type I complex and high concentration appears very stable type II complex with cytochrome P-450 Fe III. In the presence of NADPH, I-Amp gives rise to a 455 nm absorbing complex with similar properties to the Fe-RNO complexes. This complex formation was greatly enhanced with phenobarbital treated liver microsomes. The in vitro binding study shows that I-Amp and/or its metabolites was covalently bound to macromolecules in the presence of the molecular oxygen and NADPH-generating system. Incubation in the presence of glutathione, cystein and radical scavengers decreases binding. Mixed function oxydase (MFO) inhibitors diminish the amount of covalent binding and alter the extent of metabolite formation. The total covalent binding level increased with liver microsomes from PB pretreated rats as it was observed with the 455nm complex formation. The radioactivity distribution on microsomal proteins was examinated with SDS polyacrylamide gel electrophoresis and autoradiography. This experiment proves that the radiolabelled compounds are bound on the cytochrome P-450. The radioactivity bound increased when the PB induced rat liver microsomes were used. All these results indicate that I-Amp was activated by an oxydative process dependent on the MFO system which suggests a N-oxydation of I-Amp and the formation of reactive entities which covalently bind to proteins.

Single photon emission computed tomography with 99mTc HM-PAO in the study of focal epilepsy

We used 99mTc HM-PAO SPECT to study 50 patients with partial epilepsy: 47 interictally and 3 during a seizure. All 3 patients studied during a seizure presented an area of increased tracer uptake. Of those in whom recordings were taken during seizure-free intervals 35 (74%) showed perfusion asymmetries: 27 (57%) with decreased and 8 (17%) with increased uptake. We discuss the findings and compare them with those of similar studies using SPECT and positron emission tomography.

Imaging of cerebral blood flow markers in Huntington's disease using single photon emission computed tomography

Single photon emission computed tomography (SPECT) imaging of six Huntington's disease patients revealed a striking reduction in regional uptake of cerebral blood flow markers in vivo. Similar changes were found in one patient with "early stage" disease. The findings are compared with parallel magnetic resonance imaging (MRI) studies, and in one case, results of postmortem examination.

A comparison of Tc-99m HM-PAO and I-123 IMP cerebral SPECT images in Alzheimer's disease and multi-infarct dementia

SPECT images of the brain can be obtained using either 123I labelled amines or 99mTc-hexamethylpropyleneamineoxime (HM-PAO). Both materials produce images which are blood flow dominated and so appear similar in normal subjects, although the respective mechanisms of uptake are not yet finally established. It seems likely, however, that the different mechanisms of uptake are responsible for recent reports of some differences seen in images obtained with the two types of agent in patients with cerebral pathology, mainly cerebrovascular disease. In this study, 12 demented patients, 6 with dementia of the Alzheimer type (DAT) and 6 with multi infarct dementia (MID), were imaged with 123I-isopropylamphetamine (IMP) and 99mTc-HM-PAO and the images compared. Significantly more lesions were seen with IMP than HM-PAO (P less than 0.02); out of a possible 120 sites, 41 lesions were seen with IMP compared to 28 with HM-PAO, 23 being seen with both agents. However, it is concluded that either agent can be used for the differential diagnosis of dementia, a task for which the new cerebral blood flow agents seem well suited.

99mTc-HM-PAO and 123I-amphetamine cerebral scintigraphy: a new, non invasive method in determination of brain death in children

Determination of brain death in infants and children is difficult and criteria used in adult brain death are regarded insufficient in pediatric cases. In comatose children, clinical signs of brain death and EEG monitoring may be of limited value, while intercerebral blood flow estimations can provide more direct information. Beside radionuclide bolus angiography of polar radiopharmaceuticals with sequential technique, two radioisotopes are introduced for static brain images. Injection of 123I-amphetamine or the 99mTc labelled lipophilic complex HM-PAO into the peripheral venous circulation enables more precise static imaging of parenchymatous brain perfusion and cellular function in contrast to conventional dynamic imaging because of retention in the intact brain parenchyma. Critical deficits or complete loss of cerebral perfusion can be readily documented. These studies are particularly helpful when clinical signs and EEG alone cannot establish the definite diagnosis of brain death. Their easy application and wide availability renders them especially useful in children.

Initial experience with SPECT of the brain using 99mTc-hexamethyl-propyleneamine oxime (99mTc-HM-PAO)

A recently developed 99mTc radiocompound, hexamethyl-propyleneamine oxime (99mTc-HM-PAO) exhibits favorable properties for regional cerebral tomograms in man utilizing conventional instrumentation (SPECT). Planar and tomographic studies using a rotating gamma camera equipped with a high sensitivity, low energy, collimator were performed in 5 normal subjects and 20 patients suffering from different cerebral diseases. SPECT abnormalities observed in patients with CVD, brain tumors and hydrocephalus were compared with results from X-ray CT. Our preliminary study demonstrates the feasibility of assessing regional brain perfusion using SPECT and a 99mTc radiopharmaceutical which is lipid soluble and has a high extraction fraction in the brain.