Initial evaluation of 123I-5-I-R91150, a selective 5-HT2A ligand for single-photon emission tomography, in healthy human subjects

The mapping of 5-HT2 receptors in the brain using functional imaging techniques has been limited by a relative lack of selective radioligands. Iodine-123 labelled 4-amino-N-[1-[3-(4-fluorophenoxy)propyl]-4-methyl-4-piperidinyl]-5-io do-2-methoxybenzamide (123I-5-I-R91150 or 123I-R93274) is a new ligand for single-photon emission tomography (SPET), with high affinity and selectivity for 5-HT2A receptors. This study reports on preliminary 123I-5-I-R91150 SPET, whole-body and blood distribution findings in five healthy human volunteers. Maximal brain uptake was approximately 2% of total body counts at 180 min post injection (p.i. ). Dynamic SPET sequences were acquired with the brain-dedicated, single-slice multi-detector system SME-810 over 200 min p.i. Early peak uptake (at 5 min p.i.) was seen in the cerebellum, a region free from 5HT2A receptors. In contrast, radioligand binding in the frontal cortex increased steadily over time, up to a peak at approximately 100-120 min p.i. Frontal cortex-cerebellum activity ratios reached values of 1.4, and remained stable from approximately 100 min p.i. onwards. Multi-slice SPET sequences showed a pattern of regional variation of binding compatible with the autoradiographic data on the distribution of 5-HT2A receptors in humans (cerebral cortex>striatum>cerebellum). These findings suggest that 123I-5-I-R91150 may be used for the imaging of 5-HT2A receptors in the living human brain with SPET.

Correlation between reduced in vivo benzodiazepine receptor binding and severity of psychotic symptoms in schizophrenia

OBJECTIVE

Although there is evidence from postmortem studies suggestive of deficient inhibitory neurotransmission of gamma-aminobutyric acid (GABA) in schizophrenia, no direct in vivo evidence has been obtained to date. The authors used single photon emission computed tomography (SPECT) with iodine-123-labeled iomazenil ([123I]iomazenil), a radioligand that selectively binds with high affinity to the benzodiazepine subunit of the GABAA receptor complex in the human brain, to investigate the presence of benzodiazepine receptor abnormalities in the cerebral cortex of living subjects with schizophrenia.

METHOD

Dynamic [123I]iomazenil SPECT was performed in 15 patients (14 patients with DSM-III-R schizophrenia and one with schizophreniform disorder) and 12 healthy subjects over a period of 2 hours. The time-integral method was used to generate ratios of "specific" to "nonspecific" [123I]iomazenil binding at equilibrium for several cortical regions.

RESULTS

No overall between-group differences in benzodiazepine receptor binding were found, but significant correlations emerged between the severity of schizophrenic symptoms and [123I]iomazenil binding in limbic cortical regions: positive symptom scores were negatively correlated with benzodiazepine receptor binding in the left medial temporal region, and negative symptoms were inversely related to receptor binding in the medial frontal region. These correlations were not significant when a Bonferroni correction for multiple comparisons was applied.

CONCLUSIONS

These preliminary results are consistent with previous research implicating limbic cortical regions in the pathophysiology of schizophrenia, suggesting that reduced inhibitory GABAergic tone in these areas may contribute to the appearance of schizophrenic symptoms.

Non-invasive measurement of left ventricular volumes and function by gated positron emission tomography

To date cardiac positron emission tomography (PET) studies have focussed on the measurement of myocardial blood flow, metabolism and receptors while left ventricular (LV) function and dimensions have been derived from other modalities. The main drawback of this approach is the difficulty of data co-registration, which limits clinical interpretation. The aim of this study was to evaluate whether it is possible to measure absolute cardiac volumes, and consequently LV function parameters such as ejection fraction, and wall motion with gated PET. Nineteen patients underwent a PET scan and planar radionuclide ventriculography (MUGA) within 9+/-9 days. A 9-min scan (16 gates/cardiac cycle) was acquired after inhalation of 3 MBq/ml of oxygen-15 labelled carbon monoxide at the rate of 500 ml/min over 4 min using a multislice PET camera. Noise reduction was performed on the gated image to enhance the definition of the ventricles before reslicing to the short-axis view. A threshold value was used to detect the edge of the LV at each gate. LV volumes at each gate were estimated by summing the volume of voxels within the LV boundary. PET measurements of LV volumes were as follows: LV end-diastolic volume ranged from 72 to 233 ml and LV end-systolic volume ranged from 24 to 203 ml. Phantom experiments supported the validity of this approach for estimating volumes. LV ejection fraction measured with MUGA was 38.4%+/-16.3% (range 15%-71%) and that measured with PET was 39.6%+/-17.7% (range 9%-72%) (P=NS). The LV ejection fraction measurements were highly correlated (r2=0.824). These results indicate that: (1) absolute end-diastolic and end-systolic volumes can be quantified using gated PET and (2) LV ejection fraction can be accurately measured by gated PET simultaneously with the other physiological PET parameters.

Myocardial perfusion scintigraphy in patients undergoing major non-vascular abdominal surgery

The prognostic value of myocardial perfusion scintigraphy is beginning to be recognised in patients undergoing cardiovascular surgery. The aim of this prospective study was to assess the predictive value of scintigraphy in elderly patients undergoing major non-vascular abdominal surgery. Adenosine stress thallium-201 (201Tl) single-photon emission tomography (SPET) was employed for imaging using a standard protocol. Patients over the age of 60 years (n = 55) with an intermediate to high likelihood of coronary artery disease were evaluated prospectively. The clinical outcome variables analysed were cardiac mortality and major cardiac morbidity occurring within 30 days of surgery. Cardiac events were cardiac death (n = 5), angina pectoris (n = 5), nonfatal mycardial infarction (n = 1), acute left ventricular failure (n = 2) and arrhythmias requiring treatment (n = 4). All cardiac events occurred in the first 10 postoperative days except one cardiac death which happened on the 29th postoperative day. Patients with an abnormal 201Tl SPET scan had a higher risk of postoperative death (4 vs 1) or any postoperative cardiac event (13 patients vs 4 patients; P < 0.0001) when compared with those with a normal scan. The sensitivity, specificity and positive predictive value of 201Tl imaging for perioperative ischaemia and adverse outcomes were 76%, 82% and 65%, respectively. The occurrence of an intraoperative event (P < 0.02) and the length of surgery (P < 0.01) were also predictors of a postoperative cardiac event. Clinical risk variables and an abnormal electrocardiogram in isolation were poor predictors. In conclusion, preoperative myocardial perfusion scintigraphy is a valuable technique for identifying elderly patients with a high risk for cardiac events when undergoing major non-vascular abdominal surgery.

HMPAO SPECT in non-epileptic seizures: preliminary results

The diagnosis of non-epileptic seizures (NES) is problematic. Although diagnosis can be achieved by videotelemetry, these facilities are expensive and not widely available. HMPAO SPECT studies show focal hypoperfusion interictally in focal epilepsy. SPECT has not been studied in any detail in NES previously. Two groups (10 patients each) were studied, one with NES and one with complex partial seizures and localisation related epilepsy. SPECT scans were normal in 7 of 10 (70%) NES patients, while showing clear focal hypoperfusion in 8 of 10 patients (80%) with epilepsy. In the NES group, 1 patient showed hypoperfusion indistinguishable from that seen in epilepsy, while 2 patients in the epilepsy group showed only equivocal focal hypoperfusion. The remaining 2 patients in the NES group showed bifrontal and equivocal focal hypoperfusion. A normal HMPAO SPECT study supports the diagnosis of NES in patients with seizures of uncertain aetiology.

Inter-observer agreement in the reporting of 99Tcm-DMSA renal studies

The early identification of renal cortical scarring secondary to urinary reflux and/or renal infection is important in the management of patients with recurrent disease. Scintigraphic imaging of the renal cortex using 99Tcm-dimercaptosuccinic acid (DMSA) is often considered the standard method for the diagnosis of renal scars in both adults and children. Consistent reporting of 99Tcm-DMSA is nevertheless essential in ensuring that the clinician can act on the data reported. In this study, seven experienced observers were asked to report, independently, 99Tcm-DMSA data sets from 32 patients. The observers were asked to note the presence of a space occupying lesion or of a renal cortical scar(s) and to conclude if the kidney was normal or abnormal. There was marked variation in the number of renal cortical scars reported, the total number of scars seen and whether or not the kidney was normal or abnormal. After peer review of all data, consensus and referenced criteria were arrived at for a reanalysis of data. All scans were reread by the observers. There was some improvement in the concordant reporting of kidneys with renal scars (51 vs 61%) and whether or not the kidney was normal or abnormal (53 vs 63%). However, this was not statistically significant (at a level of P < 0.05). This study demonstrated significant inter-observer variation regarding the reporting of 99Tcm-DMSA studies. A consensus with agreed guidelines for data interpretation did not significantly affect this apparent lack of consistency of reporting.

Polycythaemia and agoraphobia

Using single photon emission computerized tomography (SPECT), we demonstrated that in patient A, a 20-year-old male with polycythaemia, the cerebral blood flow was decreased (presumably as a result of increased viscosity and or microemboli), probably leading to frightening visual distortions (dysmorphopsia) associated with scintillating specks of bright colors (Teichopsia). This had presumably precipitated agoraphobia. After hospitalization, when the patient had not responded to efforts at systematic desensitization, he improved through a combination of multiple venesections and antiplatelet aggregation therapy (aspirin 75 mg o.d.) over 3 months combined with systematic desensitization. A subsequent SPECT demonstrated an increase in cerebral blood flow to normal levels, which coincided with improvement of agoraphobic symptoms and disappearance of visual distortions on further follow-up. This paper depicts another yet undocumented example of an alarming physical symptom probably leading to a cognitively-based panic sufficient to cause agoraphobia by classical conditioning. It also suggests that prior treatment of such physical symptoms is likely to facilitate the process of systematic desensitization.

Gallium-67 imaging of pericardial lymphoma in AIDS

A 33-yr-old homosexual man with acquired immune deficiency syndrome (AIDS) and Mycobacterium avium intracellulare (MAI) infection presented with fever, sweats, lethargy and dyspnea. A chest radiograph showed cardiomegaly and an echocardiograph revealed a large pericardial effusion. After pericardial aspiration, which confirmed T cell non-Hodgkin's lymphoma, he remained dyspneic. Gallium-67 imaging was performed to determine whether the patient's residual dyspnea was related to pulmonary MAI infection or lymphomatous infiltration of the heart. Planar 67Ga scintigraphy revealed intense tracer uptake in two areas within the mediastinum and surrounding the entire heart shadow but no evidence of pulmonary MAI infection. SPECT 67Ga scintigraphy precisely localized the two mediastinal abnormalities and demonstrated the tracer uptake around the heart to be pericardial rather than myocardial. Gallium-67 scintigraphy suggested that pericardial lymphoma was the likely basis of the patient's dyspnea.

Dopamine D2 receptor occupancy in vivo by the novel atypical antipsychotic olanzapine--a 123I IBZM single photon emission tomography (SPET) study

We have studied striatal D2 dopamine binding in schizophrenic patients treated with the novel atypical antipsychotic drug, olanzapine. 123I iodobenzamide (IBZM) single photon emission tomography (SPET) was used to estimate striatal dopamine D2 receptor binding in vivo. Patients were recruited from a prospective, double blind controlled trial of olanzapine versus haloperidol treatment. In vivo striatal D2 binding data from olanzapine treated patients (n = 6) were compared with previously reported data from typical antipsychotic responsive (n = 10); clozapine (n = 10); and risperidone (n = 6) treated patient groups. Mean % Brief Psychiatric Rating Scale score (BPRS) improvement following olanzapine treatment was 49% (SD 44). The hypothesis that clinical improvement in olanzapine treated patients would be associated with higher mean striatal D2 binding of 123I IBZM (reflecting lower levels of D2 occupancy) than typical antipsychotic (1.25 +/- 0.05) or risperidone (1.24 +/- 0.04) treatment was confirmed. Olanzapine treated patients had similar levels of striatal D2 binding in vivo (1.41 +/- 0.06) as those treated with clozapine (1.49 +/- 0.04). This preliminary evidence suggests olanzapine is another atypical antipsychotic drug in which therapeutic response is not associated with a high degree of striatal D2 receptor occupancy in vivo.

Pathophysiology of chronic left ventricular dysfunction. New insights from the measurement of absolute myocardial blood flow and glucose utilization

BACKGROUND

Chronically dysfunctional myocardium may improve after coronary revascularization. This condition was thought to be due to a chronically reduced myocardial blood flow (MBF). Recently, however, it has been shown that in patients without previous infarction but with chronic left ventricular dysfunction, baseline MBF was normal.

METHODS AND RESULTS

To study the pathophysiology of chronic left ventricular dysfunction in patients with previous infarction, regional MBF (milliliter per minute per gram of water-perfusable tissue) and glucose utilization (MRG; micromoles per minute per gram) during hyperinsulinemic euglycemic clamp were measured with positron emission tomography in 30 patients before bypass. At baseline, 133 myocardial segments were normal, and 107 were dysfunctional. After revascularization, 59 of 107 segments improved, while 48 of 107 were unchanged. MBF was 0.92 +/- 0.25 mL.min-1.g-1 in normal segments, 0.87 +/- 0.31 mL.min-1.g-1 in improved segments (P = NS versus normal), and 0.82 +/- 0.40 mL.min-1.g-1 in unchanged segments (P < .05 versus normal). In 90% of the dysfunctional segments, MBF was > 0.42 mL.min-1.g-1, a cutoff value corresponding to the mean MBF minus 2 SD in normal segments. The MRG was 0.71 +/- 0.14 mumol.min-1.g-1 in 9 age-matched normal subjects, 0.45 +/- 0.19 mumol.min-1.g-1 (P < .01) in normal segments, 0.44 +/- 0.14 mumol.min-1.g-1 in improved segments (P = NS versus normal), and 0.34 +/- 0.17 mumol.min-1.g-1 in unchanged segments (P < .01 versus normal and improved).

CONCLUSIONS

The results suggest that resting MBF measured with 15O-labeled water in chronically dysfunctional segments is not reduced and that the myocardium of these patients is less sensitive to insulin than that of normal subjects.

Targeting disseminated melanoma with radiolabelled methylene blue: Comparative bio-distribution studies in man and animals

Targeted radiotherapy for pigmented melanoma with 3,7-(dimethylamino) phenazathionium chloride [methylene blue (MTB)] labelled with Astatine-211 (211At; alpha-particle emitter) proved to be very effective in animal model systems. Since the results justified an introduction of the treatment to the clinic, the aim of the bio-distribution studies using [123I]-MTB and [131I]-MTB in patients was to confirm selectiveness of radiolabelled MTB uptake in melanoma lesions. The investigations were carried out using planar and SPECT (single photon emission computed tomography) gamma-cameras. A stable uptake of radioiodinated MTB was found in pigmented melanomas in man, with tumour/surrounding tissue and tumour/blood ratios amounting to 9 at 19 h after a single i.v. injection. A time-dependent kinetics of radioiodinated MTB distribution was similar to that observed in human melanoma-bearing athymic mice. Blood radioactivity decreased by about 90% during the first 2.5 min after i.v. injection of the compound (T1/2biol = 0.58 min). Its retention time in various organs was either the same or very similar to that characteristic of the blood. A rapid uptake of radioiodinated MTB in the liver and kidneys confirmed the importance of these organs in excreting the compound: 25-30% of the radioactivity administered was expelled with urine over the first 24 h after the injection. There was no obvious retention of radioiodinated MTB in the brain over the observation period and in the eyes for at least the first 14 h.

Schizophrenic auditory hallucinations are associated with increased regional cerebral blood flow during verbal memory activation in a study using single photon emission computed tomography

Single photon emission tomography with split-dose technetium-99m-d, l-hexamethyl-propylene amine oxime was used to measure regional cerebral blood flow (rCBF) during a memory-activation paradigm in a group of 18 medicated DSM-III-R schizophrenic patients. The relationship between clinical features of schizophrenia and rCBF patterns was examined. Increased blood flow to the left basal ganglia was revealed during activation in patients reporting hallucinations in the previous month, a finding that was not influenced by medication dose or other confounding variables. This result adds to previous functional imaging studies that have related basal ganglia abnormalities to hallucinatory phenomena and suggests that left basal ganglia hyperactivity may be relevant to an internal monitoring deficit responsible for the appearance of those symptoms in schizophrenia.

Brainstem perfusion is impaired in chronic fatigue syndrome

We looked for brain perfusion abnormalities in patients with myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS). An initial pilot study revealed widespread reduction of regional brain perfusion in 24 ME/CFS patients, compared with 24 normal volunteers. Hypoperfusion of the brainstem (0.72 +/- 0.05 vs. 0.80 +/- 0.04, p < 0.0001) was marked and constant. We then tested whether perfusion to the brainstem in ME/CFS patients differs from that in normals, patients with major depression, and others with epilepsy. Data from a total of 146 subjects were included in the present study: 40 normal volunteers, 67 patients with ME/CFS (24 in the pilot study, 16 with no psychiatric disorders, 13 with ME/CFS and depression, 14 with ME/CFS and other psychiatric disorders), 10 epileptics, 20 young depressed patients and 9 elderly depressed individuals. Brain perfusion ratios were calculated using 99Tcm-hexamethylpropylene amine oxime (99Tcm-HMPAO) and single-photon emission tomography (SPET) with a dedicated three-detector gamma camera computer/system (GE Neurocam). Brain-stem hypoperfusion was confirmed in all ME/CFS patients. Furthermore, the 16 ME/CFS patients with no psychiatric disorders and the initial 24 patients in the pilot study showed significantly lower brainstem perfusion (0.71 +/- 0.03) than did depressed patients (0.77 +/- 0.03; ANOVA, p < 0.0001). Patients with ME/CFS have a generalized reduction of brain perfusion, with a particular pattern of hypoperfusion of the brainstem.

Regional cerebral blood flow in obsessive-compulsive disordered patients at rest. Differential correlates with obsessive-compulsive and anxious-avoidant dimensions

BACKGROUND

We tested whether cortical and subcortical regional cerebral blood flow (rCBF) differs between patients with obsessive-compulsive disorder (OCD) and healthy controls. We then explored the relationship between rCBF and OCD mental state.

METHOD

Thirty out-patients from the Maudsley Hospital with OCD as defined in DSM-III-R were scanned at rest using brain-dedicated, high-resolution, single photon emission tomography. RCBF was measured as uptake of 99mTc-HMPAO in 15 regions of interest and compared with rCBF data in 30 healthy people matched for age, sex and handedness. Symptom ratings were obtained using standard measures on the scanning day. Principal components factor analysis identified two distinct clinical dimensions: obsessive-compulsive (OC) and anxious-avoidant (AA). These were correlated with patients' rCBF measurements, using Spearman's rank correlation coefficient, and multiple regression coefficients calculated.

RESULTS

We found significant reductions in rCBF measurements of OCD patients compared with resting, healthy controls (F = 1.92, P = 0.04) in seven brain regions: the right and left superior frontal cortex, right inferior frontal cortex, left temporal cortex, left parietal cortex, right caudate nucleus and right thalamus. Regional differences were not secondary to generalised reduction in patients' brain perfusion. Reduced blood flow to the right inferior frontal cortex correlated significantly with illness severity (r = 0.37, P = 0.02). There was no relationship with age, age-of-onset, sex, handedness, depression or medication status. OC clinical dimension, concerning obsessions, compulsions and low mood, was significantly negatively correlated with left inferior frontal, medial frontal and right parietal rCBF. AA dimension, concerning anxiety and avoidance, was significantly positively associated with left and right superior frontal, right inferior frontal, medial frontal cortical, and right and left caudate and thalamic rCBF.

CONCLUSIONS

rCBF differs significantly between resting OCD patients and healthy controls, and separate clinical dimensions are associated with functionally distinct rCBF patterns.

Immunoscintigraphy with a 99Tcm-labelled anti-granulocyte monoclonal antibody in patients with human immunodeficiency virus infection and AIDS

The value of immunoscintigraphy with technetium-99m (99Tcm) labelled anti-granulocyte monoclonal antibody (BW250/183) was studied prospectively in human immunodeficiency virus (HIV-1) antibody-positive patients presenting with fever without localizing symptoms or signs. Twenty-three studies were performed in 23 patients and the results of 99Tcm-anti-granulocyte imaging were compared with the definitive microbiological or cytological diagnosis. Twenty-one patients had an infective cause of pyrexia, one patient had disseminated lymphoma and one Kaposi sarcoma. 99Tcm-anti-granulocyte antibody imaging correctly identified the sites of infection in only five (24%) patients, four of whom had infective colitis (one also had bacterial pneumonia) and one of whom had cellulitis. Sixteen foci of infection were not localized by 99Tcm-anti-granulocyte immunoscintigraphy (false-negative scans). Six of these patients had Pneumocystis carinii pneumonia; other diagnoses in this group included bacterial or fungal pneumonia and bacteraemia secondary to line infections. 99Tcm-anti-granulocyte antibody did not accumulate in the patients with disseminated lymphoma and Kaposi sarcoma (true-negative scans). 99Tcm-anti-granulocyte imaging, therefore, appears useful in identifying extrathoracic infection in HIV-1 positive patients. Its lack of sensitivity for the identification of pulmonary infection means that its role in the investigation of HIV-1 antibody-positive patients with fever without localizing symptoms or signs is limited.

Radionuclide brain imaging in acquired immunodeficiency syndrome (AIDS)

Infection with the human immunodeficiency virus-type 1 (HIV-1) may produce a variety of central nervous system (CNS) symptoms and signs. CNS involvement in patients with the acquired immunodeficiency syndrome (AIDS) includes AIDS dementia complex or HIV-1 associated cognitive/motor complex (widely known as HIV encephalopathy), progressive multifocal leucoencephalopathy (PML), opportunistic infections such as Toxoplasma gondii, TB, Cryptococcus and infiltration by non-Hodgkin's B cell lymphoma. High resolution structural imaging investigations, either X-ray Computed Tomography (CT scan) or Magnetic Resonance Imaging (MRI) have contributed to the understanding and definition of cerebral damage caused by HIV encephalopathy. Atrophy and mainly high signal scattered white matter abnormalities are commonly seen with MRI. PML produces focal white matter high signal abnormalities due to multiple foci of demyelination. However, using structural imaging techniques there are no reliable parameters to distinguish focal lesions due to opportunistic infection (Toxoplasma gondii abscess) from neoplasm (lymphoma infiltration). In this manuscript we review the use of radionuclide brain imaging techniques in the investigation of HIV infected patients. Brain perfusion single photon emission tomography (SPET), neuroreceptor and positron emission tomography (PET) studies are reviewed. Greater emphasis is put on the potential of some radiopharmaceuticals, considered to be brain tumor markers, to distinguish intracerebral lymphoma infiltration from Toxoplasma infection. SPET with 201Tl using quantification (tumour to nontumour radioactivity ratios) appears a very promising technique to identify intracerebral lymphoma.

Brain perfusion abnormalities in Gilles de la Tourette's syndrome

BACKGROUND

Functional brain imaging with technetium-99m d,l-hexamethyl propyleneamine oxime (HMPAO) Single Photon Emission Tomography (SPET) allows us to explore the cerebral pathophysiology of Gilles de la Tourette's Syndrome (GTS).

METHOD

Fifty patients and 20 controls were examined. Patients were rated for tic severity and mood. Scans were analysed quantitatively using internal ratios to the occipital cortex.

RESULTS

Patients different from controls on measures of relative blood flow to the left caudate, anterior cingulate cortex and the left dorsolateral prefrontal cortex. Severity of tics was related to hypoperfusion of the left caudate and cingulate and a left medial temporal region. Hypoperfusion in the left dorsolateral prefrontal region was related to mood.

CONCLUSIONS

The areas found to be hypoperfused in this study are consistent with known functions of fronto-striatal circuits. A wide range of perfusion patterns is seen, however, and no characteristic patterns for behavioural subgroups has been documented with this technique.

Technetium-99m-L,L-ethylenedicysteine scintigraphy in patients with renal disorders

Technetium-99m-L,L-ethylenedicysteine (99mTc-L,L-EC), a new renal imaging agent, was introduced as an alternative to 99mTc-mercaptoacetyltriglycine (MAG3). This radiopharmaceutical can be easily labelled at room temperature and has high radiochemical purity and long stability. The aim of this study was to gain clinical experience in using 99mTc-L,L-EC in normal volunteers and patients. The clearance of this radiopharmaceutical was compared with that of iodine-131 ortho-iodohippurate (OIH) in five healthy volunteers. In addition, conventional renogram and whole-body distribution of 99mTc-L,L-EC (40 min and 3 h post-injection) were evaluated in these subjects. Subsequently, ten patients with suspected obstructive nephropathy, four with renovascular disorders and two in acute renal failure were imaged. In five patients with impaired renal function both 99mTc-MAG3 and 99mTc-L,L-EC studies were performed. In each case the scintigraphic images and time/activity curves were evaluated and various semiquantitative parameters calculated and compared. No adverse effects were noted during and after 99mTc-L,L-EC scintigraphy. The mean clearance values for 99mTc-L,L-EC and 131I-OIH in volunteers were 504 and 663 ml/min respectively. The total plasma clearance of 99mTc-L,L-EC was about 75.8% of the 131I-OIH value. In volunteers the parenchymal transit time index, whole kidney transit time index and mean parenchymal transit time for 99mTc-L,L-EC were 63 s, 124 s and 175 s respectively. The mean time to peak activity was 235 s and the time from peak to 50% of peak activity was 402 s.(ABSTRACT TRUNCATED AT 250 WORDS)

Combined rest thallium-201/stress technetium-99m-tetrofosmin SPECT: feasibility and diagnostic accuracy of a 90-minute protocol

Technetium-99m tetrofosmin is a recently developed compound that clears from background organs rapidly. Tetrofosmin has a good correlation with 201Tl. This study assesses the feasibility and diagnostic accuracy of a combined protocol involving rest 201Tl SPECT and stress imaging with 99mTc-tetrofosmin.

METHODS

Twenty-five patients (23 men, 2 women; aged 36-73 yr) with known coronary artery disease underwent the combined protocol. Twenty minutes after the resting injection of 201Tl, resting SPECT data were acquired using low-energy, high-resolution collimators. A stress test using adenosine infusion combined with low-level dynamic exercise was performed. The stress data were collected 20 min later. The reconstructed vertical long-axis, horizontal long-axis and short-axis slices were analyzed qualitatively. Analysis was carried out using nine segments of the left ventricle. The segments were reported either as fixed or reversible. The results were compared to coronary angiography results.

RESULTS

The sensitivity and specificity for the detection of diseased coronary vessels were 85% and 70% for the left anterior descending territory, respectively, 78% and 71% for the right coronary artery, and 69% and 70% for the left circumflex. Overall, the sensitivity was 80% and the specificity 70%.

CONCLUSION

Combined rest 201Tl/stress 99mTc-tetrofosmin SPECT provides a protocol of short duration which displays similar diagnostic accuracy to a protocol using tetrofosmin as a single agent.

Optimised interictal HMPAO-SPECT in the evaluation of partial epilepsies

Interictal blood flow single photon emission computed tomography (SPECT) has been considered to be of limited value in the investigation of patients with partial epilepsies. Newer SPECT technologies using brain dedicated multiple detector systems have not been fully evaluated. To study the usefulness of an optimized SPECT technique, we scanned 40 epilepsy patients and ten normal subjects. Interictal [99mTc]hexamethylpropylene amine oxime (HMPAO) SPECT scans were acquired using the GE/CGR Neurocam triple-headed brain-dedicated system. The results of a qualitative analysis of the scans were compared to EEG and optimised MRI findings. Eight of the normal subjects and one of 40 patients had normal SPECT scans. There was a comparable concordance of lateralization between SPECT, MRI and EEG. The majority of our patients had mesial temporal pathology on MRI. Perfusion abnormalities extending beyond the mesial temporal area were common and did not simply relate to structural abnormalities. Quantification of blood flow in multiple brain regions revealed that hypoperfusion did not occur at random. Perfusion in the mesial temporal lobe was related to perfusion in anatomically and functionally related ipsilateral and contralateral brain regions. These hypoperfused areas probably reflect dysfunctioning areas which are related to the epileptogenic process.

Clinical brain radionuclide imaging studies

A recent survey of the knowledge and practice of both positron-emission tomography (PET) and single-photon emission computed tomography (SPECT) of the brain among referring physicians in Europe (neurologists and psychiatrists) showed a disquieting lack of knowledge of the potential of these methodologies in the investigation and management of patients of their own specialities. The need to bring the knowledge of the potential of these techniques to the practicing physicians is paramount. It is imperative that the methodologies and concepts that preside over the application of these techniques in neurology and psychiatry must become more uniform if an impact is to be felt at a clinical level. There is clear improvement in the instrumentation available with the new state-of-the-art tomographic devices and with the development of new technetium-based radiopharmaceuticals for the study of cerebral perfusion. The constant progress made with ligands that permit the study of neurotransmission, tumor metabolism, and turnover do expand our capability to improve the knowledge concerning neurophysiology, neuropathology, and neuropharmacology of a variety of disease states. PET and SPECT will be progressively included in protocols aimed at stratifying patients with dementia, monitoring therapeutic trials, and improving our ability to determine outcome. Clinical usefulness of PET and SPECT begin to emerge in cerebral vascular disease, in the identification of cerebral death, in epilepsy, in cerebral trauma, in the investigation of HIV-positive patients with cerebral involvement, and in the monitoring of tumor recurrence and postirradiation damage. This review article outlines a current perspective of SPECT and PET as practiced in Europe, its potential, and its limitations.

Patterns of regional cerebral blood flow in corticobasal degeneration studied using HMPAO SPECT; comparison with Parkinson's disease and normal controls

Corticobasal degeneration (CBD) is a rare syndrome characterised by an asymmetrical rigidity with localised cortical signs, particularly apraxia. Using positron emission tomography, abnormal patterns of cortical metabolism have recently been shown. We have studied patterns of regional cerebral blood flow (rCBF) using single photon emission tomography, with the tracer 99Technetium hexamethylpropylenamine (HMPAO), in subjects with CBD. In subjects with CBD, compared with 12 age-matched normal controls, in the clinically more affected hemisphere a characteristic pattern was found with significant reductions in HMPAO uptake in the posterior frontal cortex (by 11.5%), and in the superior, inferior, anterior, and posterior parietal cortex (by 12.2, 12.9, 12.9, and 9.7, respectively). Reduced uptake was also found in the caudate (9.3%), putamen (9.7%), and thalamus (8.6%). In contrast, HMPAO uptake in the temporal and occipital cortex was normal. In comparison with 12 Parkinson's disease (PD) controls, significant reduced uptake was seen in the thalamus (9.0%), posterior frontal (8.9%), and inferior (9.9%), and anterior parietal (9.5%) cortex. A similar pattern of impaired uptake was seen in the clinically less/unaffected cerebral hemisphere in patients with CBD compared with normal controls, with a significant reduction in HMPAO uptake in the thalamus (6.8%), superior parietal (9.6%) and anterior parietal (7.6%), and posterior parietal (7.3%) cortex. This implies that the disease process is bilateral even in those cases with clinically unilateral disease. This widely available technique may be useful in the early diagnosis of CBD and in differentiation from other extrapyramidal disorders.

In vivo imaging of GABAA receptors using sequential whole-volume iodine-123 iomazenil single-photon emission tomography

Using a brain-dedicated triple-headed single-photon emission tomography (SPET) system, a sequential whole-volume imaging protocol has been devised to evaluate the regional distribution of iodine-123 iomazenil binding to GABAA receptors in the entire brain. The protocol was piloted in eight normal volunteers (seven males and one female; mean age, 24.8 +/- 3.9 years). The patterns obtained were largely compatible with the known distribution of GABAA receptors in the brain as reported in autoradiographic studies, with cerebral cortical regions, particularly the occipital and frontal cortices, displaying the highest 123I-iomazenil uptake. Measures of time to peak uptake and tracer washout rates presented with the same pattern of regional variation, with later times to peak and slower washout rates in cortical regions compared to other brain areas. Semiquantitative analysis of the data using white matter/ventricle regions as reference demonstrated a plateau of specific 123I-iomazenil binding in neocortical and cerebellar regions from 60-75 min onwards. These data demonstrate the feasibility of sequential, dynamic whole-volume 123I-iomazenil SPET imaging. The protocol may be particularly useful in the investigation of neuropsychiatric conditions which are likely to involve more than one focus of GABA abnormalities, such as anxiety disorders and schizophrenia.