Limited performance of quantitative assessment of myocardial function by thallium-201 gated myocardial single-photon emission tomography

We investigated the reproducibility between thallium-201 and technetium-99m methoxyisobutylisonitrile (MIBI) gated single-photon emission tomography (SPET) for the assessment of indices of myocardial function such as end-diastolic and end-systolic volume (EDV, ESV), ejection fraction (EF) and wall motion. Rest ²⁰¹Tl (111 MBq) gated SPET was sequentially performed twice in 20 patients. Rest ²⁰¹Tl gated SPET and rest ^99mTc-MIBI (370 MBq) gated SPET were performed 24 h apart in 40 patients. Wall motion was graded using the surface display of the Cedars quantitative gated SPET (QGS) software. EDV, ESV and EF were also measured using the QGS software. The reproducibility of functional assessment on rest ²⁰¹Tl gated SPET was compared with that on ^99mTc-MIBI gated SPET, and also with that between ²⁰¹Tl gated SPET and ^99mTc-MIBI gated SPET performed on the next day. The two standard deviation (2 SD) values for EDV, ESV and EF on the Bland-Altman plot were 29 ml, 19 ml and 12%, respectively, on repeated ²⁰¹Tl gated SPET, compared with 14 ml, 11 ml and 5.3% on repeated ^99mTc-MIBI gated SPET. The correlations were good (r=0.96, 0.97 and 0.87) between the two measurements of EDV, ESV and EF on repeated rest studies with ²⁰¹Tl and ^99mTc-MIBI gated SPET. However, Bland-Altman analysis revealed that the 2 SD values between the two measurements were 31 ml, 23 ml and 12%. We were able to score the wall motion in all cases using the 3D surface display of the QGS on ²⁰¹Tl gated SPET. The kappa value of the wall motion grade on the repeated ²⁰¹Tl study was 0.35, while that of the wall motion grade on the repeated ^99mTc-MIBI study was 0.76. The kappa value was 0.49 for grading of wall motion on repeated rest studies with ²⁰¹Tl and ^99mTc-MIBI. In conclusion, QGS helped determine EDV, ESV, EF and wall motion on ²⁰¹Tl gated SPET. Because the EDV, ESV and EF were less reproducible on repeated ²⁰¹Tl gated SPET or on ²⁰¹Tl gated SPET and ^99mTc-MIBI gated SPET on the next day than on repeated ^99mTc-MIBI gated SPET, functional measurement on ²⁰¹Tl gated SPET did not seem to be interchangeable with that on ^99mTc-MIBI gated SPET. Received 18 May 1999 and in revised form 4 October 1999     

Simultaneous dual-isotope technetium-99m/thallium-201 cardiac SPET imaging using a projection-dependent spilldown correction factor

A spilldown correction method is proposed for the thallium-201 window image in simultaneous dual-isotope technetium-99m/thallium-201 single-photon emission tomographic (SPET) imaging based on a single acquisition into three energy windows. In this method, images are simultaneously acquired in two standard energy windows over the^99mTc and²⁰¹Tl photopeak regions and a third spilldown window adjacent to the²⁰¹Tl window. Using a Monte Carlo simulation of SPET, the fractional amount of^99mTc and²⁰¹Tl spilldown in the²⁰¹Tl window with respect to the total counts from the spilldown window, k12, was calculated for simulated images of point sources at varying depths within a water-filled elliptical tub phantom. When applied to experimental acquisitions, k12, multiplied by the total counts from the spilldown window, is then subtracted from the²⁰¹Tl window image to produce the corrected image. However, for successful applications in SPET, k12 must be determined on a projection-by-projection basis since k12 is depth dependent. Thus, a regression relation was obtained between k12 and the total count ratio of the spilldown to^99mTc windows, k23. The spilldown correction method was applied to²⁰¹T1 photopeak images of an extended source distribution in uniform and nonuniform attenuating media with dual-isotope^99mTc/²⁰¹Tl and single-isotope²⁰¹Tl. A marked improvement in image contrast was observed between the corrected and uncorrected²⁰¹Tl window images. The average count ratio of uncorrected dual-isotope²⁰¹Tl/single-isotope²⁰¹Tl was 3.08 for uniform and 2.99 for non-uniform attenuating media. When corrected, this value approached unity (0.97 and 1.08) and the corrected dual-isotope images were visually similar The presented method in which spilldown correction for the²⁰¹Tl photopeak window is performed in a single acquisition on a projection-by-projection basis in simultaneous dual-isotope SPET imaging could form the basis for a rapid and accurate clinical dual-isotope protocol independent of radiotracer administration.     

“Luxury perfusion” with99mTc-HMPAO and123I-IMP SPECT imaging during the subacute phase of stroke

To compare the merits of¹²³I-isopropyl-iodoam-phetamine (¹²³I-IMP) and^99mTc-HMPAO in showing abnormal brain uptake distribution during cerebral ischemia, we studied ten patients during the subacute phase of their stroke, a period where metabolism and blood flow are frequently uncoupled. SPECT imaging was performed using both radiopharmaceuticals in the 10 patients from 48 h to 4 weeks after onset of symptoms. Two patients out of the 10 had similar defects with¹²³I-IMP and^99mTc-HMPAO SPECT, the location of the defects corresponding to the area of infarction observed on CT. Six patients had normal^99mTc-HMPAO SPECT and abnormal¹²³I-IMP SPECT with defects in the area of infarction shown by CT. The remaining 2 patients had hyperactive abnormalities on^99mTc-HMPAO in areas corresponding to defects on the¹²³I-IMP images. Two of the patients with SPECT mismatches were studied again more than 1 month after onset. On reexamination,^99mTc-HMPAO SPECT which was previously normal or hyperactive became hypoactive with a focal area of decreased activity corresponding to the defect on¹²³I-IMP. Crossed cerebellar diaschisis was found in 7 patients with^99mTc-HMPAO and was absent for both¹²³I-IMP and^99mTc-HMPAO in 3. We suggest that SPECT with⁹⁹mTc-HMPAO could show transient hyperemia not demonstrated by¹²³I-IMP whereas in some cases cerebral infarction would be more difficult to demonstrate with^99mTc-HMPAO than with¹²³I-IMP. SPECT with both tracers is recommended to follow the evolution of strokes in terms of regional cerebral blood flow and tissue metabolism.     

Regional differences between <Superscript>99m</Superscript>Tc-ECD and <Superscript>99m</Superscript>Tc-HMPAO SPET in perfusion changes with age and gender in healthy adults

A number of studies using single-photon emission tomography (SPET) have shown perfusion changes with age in several cortical and subcortical areas, which might distort the results of perfusion imaging studies of neuropsychiatric disorders. Technetium-99m labelled ethyl cysteinate dimer (ECD) and hexamethylpropylene amine oxime (HMPAO) are both used as markers of cerebral perfusion, but have different pharmacokinetics and retention patterns. The aim of this study was to determine whether age and gender effects on perfusion SPET differ depending on whether ^99mTc-HMPAO or ^99mTc-ECD is used. Forty-five subjects (20 male and 25 female, mean age 52.8±6.6 years) were assigned to ^99mTc-HMPAO SPET (HMPAO group), and 39 subjects (24 male and 15 female, mean age 52.6±6.7 years) to ^99mTc-ECD SPET (ECD group). SPET images were obtained about 10 min after intravenous injection of approximately 800 MBq ^99mTc-HMPAO or ^99mTc-ECD using the same SPET scanner. Three-dimensional volumetric magnetic resonance imaging was performed to as7sess morphological changes in the grey matter. All image processing and statistical analyses were performed using SPM99 software. An area in the right anterior frontal lobe showed an increase in perfusion with age only in the HMPAO group, whereas areas in the bilateral retrosplenial cortex showed decreases in perfusion with age only in the ECD group; neither group showed corresponding changes in the grey matter. The present study shows that different effects of age on perfusion are observed depending on whether ^99mTc-HMPAO and ^99mTc-ECD is used. This suggests that the results of perfusion SPET are differently confounded depending on the tracer used, and that perfusion SPET with these tracers has limitations when used in research on subtle perfusion changes.     

Visualization of posture-dependent cerebral blood flow in a patient with Takayasu's disease by means of 99mTc-HMPAO brain single photon emission tomography

A case of Takayasu's disease in a 22-year-old woman who complained of severe fainting attacks is presented. Bilateral obstruction of the cervical arteries was confirmed by digital subtraction angiography. Preoperative technetium-99m hexamethylpropylene amine oxime brain SPET in the sitting position showed bilateral hypoactivity in the temporoparietal areas. Subtraction brain SPET showed slightly increased activity in the lying position. The patient has had no fainting attacks since bypass surgery. Postoperative ^99mTc-HMPAO brain SPET in the sitting position showed normal activity except in the right temporoparietal area. This area was filled in the lying position. ^99mTc-HMPAO brain SPET is the only technique that can visualize the cerebral blood flow in any position, this capability deriving on the fact that the distribution of ^99mTc-HMPAO in the brain is fixed in the first 2–3 min following injection. The use of both sitting and lying ^99mTc-HMPAO brain SPET is very useful for detecting an abnormality (i.e. an inhomogeneous response due to the fall in perfusion pressure) that could not be seen if the cerebral blood flow were to be assessed only in the lying position. Correspondence to: K. Hayashida     

SPET brain imaging with 201 diethyldithiocarbamate in acute ischaemic stroke

Thirty-five patients with acute ischaemic stroke were studied within 24 h after hospital admission with thallium 201 diethyldithiocarbamate single photon emission tomography (²⁰¹TI-DDC SPET) and X-ray computed tomography (CT).²⁰¹TI-DDC is a non-redistributing agent that allows postponed imaging after early administration and early therapeutic intervention. In 16 patients both investigations were performed within 24 h after stroke onset. The sensitivity of SPET was 94% and of CT 81 % in the first 24 h, when hypodensity and obliteration of sulci were used as CT reading criteria. When only hypodensity was used as a criterion, the sensitivity of CT was 50% in this group. Sensitivity of CT compared with SPET became increasingly better in patients with older infarcts (1–18 days). In two-thirds of patients, the lesion demonstrated on SPET was larger than that on CT, and this was especially so with older infarcts. Crossed cerebellar diaschisis occurred in 69% of patients. The high sensitivity of²⁰¹TI-DDC SPET in the first 24 h after ischaemic stroke and the favourable properties of this radiopharmaceutical make it a method of interest in the assessment of initial perfusion defects in early experimental stroke therapies.     

Evaluation of radiotherapeutic response in non-small cell lung cancer patients by technetium-99m MIBT and thallium-201 chloride SPET

The purpose of this study was to investigate the relationship between technetium-99m hexakis-2-methoxyisobutylisonitrile (^99mTc-MIBI) accumulation in tumours and response to radiotherapy in non-small cell lung cancer patients in comparison with the findings obtained using thallium-201 chloride (²⁰¹Tl).Simultaneous dual single-photon emission tomography (SPET) imaging with 600 MBq ^99mTc-MIBI and 111 MBq ²⁰¹Tl was performed in 31 patients with biopsy- or sputum cytology-proven lung cancer. SPET images were acquired 15 min (early) and 2 h (delayed) after injection, and the early ratio, delayed ratio and retention index were measured. The tumours were classified into two groups on the basis of follow-up computed tomography (CT): responders (at least 50% reduction in tumour size) and non-responders (little or no change in tumour size).The mean (± SD) values of early ratio, delayed ratio and retention index using ^99mTc-MIBI SPET were 3.0±1.1, 2.7±1.0 and –9.5±12.7, respectively, in responders and 2.4±0.7, 2.0±0.5 and –18.4±9.0, respectively, in non-responders. The corresponding values using ²⁰¹Tl chloride SPET were 3.7±1.0, 4.7±1.5 and 24.2±22.1 in responders and 3.3±1.2, 4.0±1.3 and 20.4±20.5 in non-responders. Using ^99mTc-MIBI, the delayed ratio and retention index in responders were significantly higher than those in non-responders (P<0.01 and P<0.05, respectively). The results of this study indicate that patients with higher delayed ratio and retention index values using ^99mTc-MIBI SPET are likely to respond better to radiotherapy than those with lower values. ^99mTc-MIBI SPET may give an indication of the short-term response to radiotherapy in patients with non-small cell lung cancer. Received 1 November 1999 and in revised form 8 January 2000     

A quantitative approach to technetium-99m ethyl cysteinate dimer: a comparison with technetium-99m hexamethylpropylene amine oxime

To develop non-invasive regional cerebral blood flow (rCBF) measurements using technetium-99m ethyl cysteinate dimer (^99mTc-ECD) and single-photon emission tomography (SPET), the same graphical analysis as was described in our previous reports using technetium-99m hexamethylpropylene amine oxime (^99mTc-HMPAO) was applied to time-activity data for the aortic arch and brain hemispheres after intravenous injection of^99mTc-ECD. Hemispherical brain perfusion indices (BPI) for^99mTc-ECD showed a highly significant correlation (n = 22,r = 0.935,P = 0.0001) with those for^99mTc-HMPAO in 11 patients who underwent both tracer studies. Using both linear regression line equations between^99mTc-ECD BPI and^99mTc-HMPAO BPI and between^99mTc-HMPAO BPI and mean cerebral blood flow (CBF) values obtained from a xenon-133 inhalation SPET method in a previous study,^99mTc-ECD BPI was converted to¹³³Xe CBF values (y = 2.60x + 19.8). Then raw SPET images of^99mTc-ECD were converted to rCBF maps using Lassen's correction algorithm. In this algorithm, the correction factor a was fixed to 1.5, 2.6 and infinite. In the comparison of rCBF values for^99mTc-ECD SPET with those for^99mTc-HMPAO SPET in 396 regions of interest in the aforementioned 11 patients, the fixed correction factor of 2.6 gave nearly the same rCBF values for^99mTc-ECD (50.1 ± 16.9 ml/100 g/min, mean ± SD) as for^99mTc-HMPAO (49.9 ± 17.3 ml/100 g/min). In conclusion, the same non-invasive method as has been used in^99mTc-HMPAO studies is applicable to a^99mTc-ECD study for the measurement of rCBF without any blood sampling.     

The value of gallium-67 and thallium-201 whole-body and single-photon emission tomography images in dialysis-related β2-microglobulin amyloid

The aim of this study was to investigate the value of gallium-67 and thallium-201 whole-body and single-photon emission tomography (SPET) images in long-term dialysis patients in whom dialysis-related β₂-microglobulin amyloid (β₂-MA) was clinically suspected. Twenty-three patients who had received dialysis for at least 10 years were included in the study. A technetium-99m methylene diphosphonate (MDP) whole-body scan was performed in all of the patients. If there was any MDP accumulation in the articular and/or peri-articular region, ⁶⁷Ga and ²⁰¹Tl whole-body and SPET images were then acquired. If any ⁶⁷Ga and/or ²⁰¹Tl uptake was observed, a CT-guided biopsy was done. In those patients who had articular and/or peri-articular uptake of ^99mTc MDP, ⁶⁷Ga and/or ²⁰¹Tl and who were pathologically proven to have β₂-MA, ^99mTc MDP, ⁶⁷Ga and ²⁰¹Tl whole-body scans and SPET were carried out again, both 3 months and 1 year after initiation of treatment. This served to evaluate the therapeutic effect and allowed comparison with the clinical findings. Of the 23 patients, eight had abnormal ^99mTc MDP uptake. Among these eight, six had intense ^99mTc MDP, ⁶⁷Ga and ²⁰¹Tl uptake in the articular and peri-articular regions before medication. Three months after the start of treatment, there were very marked decreases in uptake on both the ⁶⁷Ga and ²⁰¹Tl scans but less obvious changes in uptake of ^99mTc-MDP. In comparison with the other clinical manifestations such as limitation in range of motion, the more the painful disability improved, the less was the uptake on both ⁶⁷Ga and ²⁰¹Tl scans. There were virtually no differences in uptake pattern between the three scans of each radiopharmaceutical obtained for each patient in both 3 months and 1 year after initial of treatment. It is concluded that ^99mTc-MDP whole-body bone scan can both detect active and pre-existing inactive deposits of β₂-MA. ⁶⁷Ga and ²⁰¹Tl scans are helpful to differentiate active from inactive deposits of β₂-MA and to evaluate the therapeutic effect on these patients. SPET images are usually needed to distinguish articular and peri-articular lesions from bone lesions. Received 19 May and in revised form 9 August 1999     

Different uptake of 99mTc-ECD and 99mTc-HMPAO in the same brains: analysis by statistical parametric mapping

The purpose of this study was to investigate the differences between technetium-99m ethyl cysteinate dimer (^99mTc-ECD) and technetium-99m hexamethylpropylene amine oxime (^99mTc-HMPAO) uptake in the same brains by means of statistical parametric mapping (SPM) analysis. We examined 20 patients (9 male, 11 female, mean age 62ᆠ years) using ^99mTc-ECD and ^99mTc-HMPAO single-photon emission tomography (SPET) and magnetic resonance imaging (MRI) of the brain less than 7 days after onset of stroke. MRI showed no cortical infarctions. Infarctions in the pons (6 patients) and medulla (1), ischaemic periventricular white matter lesions (13) and lacunar infarction (7) were found on MRI. Split-dose and sequential SPET techniques were used for ^99mTc-ECD and ^99mTc-HMPAO brain SPET, without repositioning of the patient. All of the SPET images were spatially transformed to standard space, smoothed and globally normalized. The differences between the ^99mTc-ECD and ^99mTc-HMPAO SPET images were statistically analysed using statistical parametric mapping (SPM) 96 software. The difference between two groups was considered significant at a threshold of uncorrected P values less than 0.01. Visual analysis showed no hypoperfused areas on either ^99mTc-ECD or ^99mTc-HMPAO SPET images. SPM analysis revealed significantly different uptake of ^99mTc-ECD and ^99mTc-HMPAO in the same brains. On the ^99mTc-ECD SPET images, relatively higher uptake was observed in the frontal, parietal and occipital lobes, in the left superior temporal lobe and in the superior region of the cerebellum. On the ^99mTc-HMPAO SPET images, relatively higher uptake was observed in the medial temporal lobes, thalami, periventricular white matter and brain stem. These differences in uptake of the two tracers in the same brains on SPM analysis suggest that interpretation of cerebral perfusion is possible using SPET with ^99mTc-ECD and ^99mTc-HMPAO.     

Assessment of non-reperfused and reperfused myocardial infarction using diffusible or deposited radiolabelled perfusion imaging agents

Purpose Incomplete microvascular reperfusion is often observed in patients undergoing thrombolytic therapy or angioplasty for acute myocardial infarction and has important prognostic implications. We compared the myocardial uptake of diffusible (²⁰¹Tl) and deposited (^99mTcN-NOET) perfusion imaging agents in the setting of experimental infarction. Methods Rats were subjected to permanent coronary occlusion (OCC, n=10) or to 45-min occlusion and reperfusion (REP, n=17). Seven days later, the tracers were co-injected and the animals were euthanised 15 min (all ten rats in the OCC group and 12 rats in the REP group) or 120 min (five rats from the REP group, euthanised at this time point to evaluate any redistribution of the tracers: REP-RED group) afterwards. Infarct size determination and ^99mTcN-NOET/²⁰¹Tl ex vivo imaging were performed. Regional flow and tissue oedema were quantified using radioactive microspheres and ^99mTc-DTPA, respectively. Results ^99mTcN-NOET and ²⁰¹Tl defect magnitudes were similar in OCC animals (0.11±0.01 vs 0.13±0.01). In REP animals, ²⁰¹Tl defect magnitude (0.25±0.02) was significantly lower than the magnitude of ^99mTcN-NOET and flow defects (0.14±0.03 and 0.17±0.01, respectively; p<0.05), despite the lack of ²⁰¹Tl redistribution (REP-RED animals). ^99mTc-DTPA indicated the presence of oedema in the reperfused area. Blood distribution studies showed that, unlike ^99mTcN-NOET, ²⁰¹Tl plasma activity was mostly unbound to plasma proteins. Conclusion ^99mTcN-NOET and ²⁰¹Tl delineated the non-viable area in chronic non-reperfused and reperfused myocardial infarction. The significantly decreased ²⁰¹Tl defect in reperfused infarction was likely due to partial diffusion of the tracer from the plasma into the oedema present in the infarcted area. Deposited perfusion tracers might be better suited than diffusible agents for the assessment of regional flow following reperfusion of myocardial infarction.     

Avid thallium-201 uptake in hepatic carcinoid metastases

While radiolabelled somatostatin analogues sensitively detect extrahepatic carcinoid tumour, intrahepatic metastases are frequently not visualised due to somatostatin accumulation in normal hepatic tissues. We report a case of avid thallium-201 uptake in multiple hepatic carcinoid metastases using single-photon emission tomography (SPET) and compare this to a SPET technetium-99m sulphur colloid scan in the same patient. The ^99mTc sulphur colloid images demonstrate multiple focal defects at the site of known metastases in the hepatic right lobe (confirmed on both CT and surgery). However, there is avid uptake of thallium in the metastases on comparative SPET slices. ²⁰¹Tl may be a useful agent for the detection and localisation of carcinoid tumour and in particular of intrahepatic carcinoid metastases. Correspondence to: R.J. Quinn     

Myocardial uptake of thallium 201 and technetium 99m-labeled sestamibi after ischemia and reperfusion: Comparison by quantitative dual-tracer autoradiography in rabbits

Background  

Myocardial scintigraphy with^99mTc-labeled sestamibi (^99mTc-sestamibi) or²⁰¹Tl is used to assess regional perfusion in acute coronary syndromes associated with metabolic or functional abnormalities, such as acute coronary thrombosis with reperfusion and ischemia at rest. However, the initial uptake of these agents may be affected by a recent ischemic insult because the myocardial retention of these tracers depends on cellular metabolism.     

Brain single-photon emission tomography with technetium-99m hexamethylpropylene amine oxime in adolescents with initial-stage schizophrenia

The objective of this study was to search for regional cerebral blood flow (rCBF) abnormalities in adolescents with initial-stage schizophrenia by means of brain single-photon emission tomography (SPET) using technetium-99m hexamethylpropylene amine oxime (HMPAO). SPET studies were performed on a homogeneous sample of 15 carefully selected adolescents with a recent diagnosis of schizophrenia, and without previous electroconvulsive or antipsychotic drug treatment. Computed tomography (CT) and electro-encephalographic (EEG) studies were performed in all patients. Qualitative and semiquantitative analysis of^99mTc-HMPAO SPET studies showed an impaired rCBF in 12 patients (80%). The most common pattern was a decreased uptake of^99mTc-HMPAO in the frontal lobes, usually in the left hemisphere. Conventional and quantitative EEG was positive in 12 (80%) and 15 (100%) patients, respectively. CT findings were positive in two patients (13%). There was a high level of concordance between SPET and EEG results and between SPET and clinical features (P>0.05). This study suggests that previously untreated patients in the first stages of schizophrenia present functional abnormalities that are revealed by brain SPET.     

Benzodiazepine receptors and cerebral blood flow in partial epilepsy

It was the aim of this study to compare benzodiazepine (Bz) receptor binding and cerebral perfusion in patients with partial epilepsy. Single photon emission tomography (SPET) studies with the flow-marker technetium 99m hexamethylpropylene amine oxine (^99mTc-HMPAO) and with the¹²³I-labelled Bz-receptor ligand Ro 16-0154 (¹²³I-Iomazenil) were performed in 12 patients with partial epilepsy, all with normal magnetic resonance imaging (MRI) and computed tomography (CT) scans. The SPET studies with¹²³I-Iomazenil were carried out 5 min and 2 h after injection. At 2 h the distribution of activity was very similar to the expected distribution of Bz-receptors in the human brain, known from positron emission tomography (PET) work and post-mortem studies. Early images showed a significantly higher tracer accumulation in the area of the basal ganglia, cerebellum, and naso-pharyngeal space. This finding is caused by non-specific binding and the contribution of the tracer in the blood pool in this phase. Also after 2 h p.i. of¹²³I-Iomazenil, 9 of the 12 patients showed a focal decrease of of Bz-receptor binding. Ten patients had focal flow abnormalities with^99mTc-HMPAO SPET. In 8 subjects impairment of flow was seen in sites of reduced¹²³I-Iomazenil uptake.¹²³I-Io-mazenil is suitable for Bz-receptor mapping. In this series of patients, Bz-receptor mapping with SPET seems to offer no advantage over^99mTc-HMPAO in the detection of epileptic foci. Offprint requests to: P. Bartenstein     

Combination of early and delayed SPET imaging using technetium-99m ethyl cysteinate dimer immediately after local intra-arterial thrombolysis

The aim of this study was to investigate the prognostic utility of post-treatment technetium-99m ethyl cysteinate dimer (^99mTc-ECD) single-photon emission tomography (SPET) for predicting ischemic tissue outcome in cases involving embolic middle cerebral artery occlusion treated with local intra-arterial thrombolysis. We examined twenty-five patients with a moderately ischemic area determined using pretreatment technetium-99m hexamethylpropylene amine oxime (^99mTc-HMPAO) SPET, and with complete recanalization within 6 h. Post-treatment ^99mTc-ECD SPET studies, consisting of scanning for 0.5-6.5 min (early scan) and 15-21 min (delayed scan) after tracer injection, were performed immediately after thrombolysis. The extent of the affected area outlined on pretreatment ^99mTc-HMPAO SPET was used for the post-treatment early and delayed ^99mTc-ECD SPET images, and the AR/CE ratio (ratio of affected regional activity to cerebellar activity) was calculated. The washout index of ^99mTc-ECD in the affected area was also calculated by dividing the difference between the AR/CE ratio in the early and delayed images by the AR/CE ratio in the early image. Twelve patients without infarction or with small subcortical/basal ganglial infarction, ten with medium or large cortical infarction, and three with hemorrhage were identified by follow-up computed tomography. Although the AR/CE ratio in post-treatment early ^99mTc-ECD SPET images was significantly higher in the hemorrhagic group than in the cortical infarction group, this value did not differentiate the reversible ischemia group from either the cortical infarction or the hemorrhagic group. The AR/CE ratio in post-treatment delayed ^99mTc-ECD SPET images statistically differentiated the reversible ischemia group from both the cortical infarction and the hemorrhagic group. However, the difference between the cortical infarction and hemorrhagic groups was not statistically significant. The washout index of ^99mTc-ECD statistically differentiated all three groups. This study demonstrated that a combination of early and delayed ^99mTc-ECD SPET imaging performed immediately after thrombolysis predicts ischemic tissue outcome.     

Comparison of thallium-201 SPET and CT/MRI in the detection of residual/recurrent squamous cell carcinoma of the oral cavity

This study was designed to compare the effectiveness of thallium-201 single-photon emission tomography (SPET) and conventional imaging, comprising computed tomography (CT) and magnetic resonance imaging (MRI), in the detection of residual/recurrent squamous cell carcinoma (SCC) of the oral cavity. Thirty-two patients with clinically suspected recurrent SCC of the oral cavity were recruited. All patients underwent ²⁰¹Tl SPET and CT or MRI within 2 weeks. The final diagnoses were based on the histology of the biopsy specimen. ²⁰¹Tl SPET and CT/MRI both accurately detected 17 of 18 residual/recurrent tumours. CT/MRI yielded eight false-positive studies, whereas ²⁰¹Tl SPET successfully excluded all tumours. The sensitivity, specificity, positive and negative predictive values and accuracy of ²⁰¹Tl SPET for the detection of recurrent oral SCC were 94%, 100%, 100%, 93% and 97%, respectively. The sensitivity, specificity, positive and negative predictive values and accuracy of CT/MRI for the detection of recurrent oral SCC were 94%, 43%, 68%, 86% and 72%, respectively. Thallium-201 SPET is more accurate than conventional imaging (CT or MRI) in differentiating residual/recurrent oral SCC from post-therapy changes.     

Visualization of pressure-dependent luxury perfusion in a patient with subacute cerebral infarction

Luxury perfusion characterized by depressed metabolism compared with CBF might be changed by decreasing cerebral perfusion pressure during the sitting position. A 77-yr-old man with subacute cerebral infarction was studied with brain X-ray computed tomography (CT), raise-up test with^99mTc-d,1-hexamethylpropyleneamine oxime (HMPAO) brain single photon emission tomography (SPECT) and positron emission tomography (PET). Brain X-ray CT revealed a low-density area in the left middle cerebral artery (MCA) anterior area. Raise-up^99mTc-HMPAO brain SPECT revealed decreased uptake in the left MCA anterior area in the sitting position and subsequent supine^99mTc-HMPAO brain SPECT revealed hot accumulation there. PET study in the supine position demonstrated some differences between CBF and the cerebral metabolic rate for oxygen in the left MCA anterior area, indicating luxury perfusion. CBF in the area of luxury perfusion might be decreased during the sitting or standing position and increased during the supine position by dysautoregulation of the cerebral vessels in the luxury perfusion during the subacute infarct.     

Recovery of impaired left ventricular function in patients with acute myocardial infarction is predicted by the discordance in defect size on123I-BMIPP and201TI SPET images

A discrepancy between myocardial perfusion defect and wall motion abnormalities is frequently found early after coronary reperfusion in patients with acute myocardial infarction. The purpose of this study was to assess recovery of impaired left ventricular function by reference to the discordance in defect size between myocardial fatty acid uptake and myocardial perfusion using combined single-photon emission tomographic (SPET) imaging early after coronary perfusion therapy. In 37 patients with acute myocardial infarction, iodine-123 15(p-iodophenyl)-3(R, S)-methylpentadecanoic acid (BMIPP) and thallium-201 SPET scans were performed early after coronary reperfusion. A severity score was determined from the extent of the imaging defect with each tracer. Left ventricular wall motion score (WMS) and ejection fraction (EF) were obtained at admission and at 4 weeks after the onset of infarction. In 32 of the 37 patients, discordance in defect sizes delineated with the two SPET studies was found during the acute stage. The severity score for BMIPP was larger than that for²⁰¹Tl during the acute stage (7.7±2.4 vs 4.4±2.5,P <0.001). There was a fair correlation between the severity score for BMIPP and WMS (r=0.82,P <0.0001), but a poor correlation between that for²⁰¹Tl and WMS. The extent of discordance in severity scores between BMIPP and²⁰¹Tl during the acute stage correlated well with the extent of the improvement in WMS (r=0.86,P <0.0001) and that of EF (r=0.85,P <0.0001). We conclude that the discordance in defect size on BMIPP and²⁰¹TI SPET images during the acute stage of infarction is an early predictor of the viability of the myocardium at risk of infarction.     

Nitrate administration to enhance the detection of myocardial viability by technetium-99m tetrofosmin single-photon emission tomography

A comparison was performed between technetium-99m tetrofosmin myocardial perfusion tomography at baseline and after nitrate administration, using a 2-day protocol, and rest-reinjection thallium-201 single-photon emission tomography (SPET) studies in order to assess whether nitrates enhance the detection of viable myocardium with^99mTc-tetrofosmin. Fifteen patients with coronary artery disease, previous myocardial infarction and a left ventricular ejection fraction <40% underwent²⁰¹T1 rest-injection and^99mTc-tetrofosmin. baseline-postnitroglycerin (0.4 mg sublingually) SPET studies, within 48 h. Tomograms based on the three spatial planes were divided into 15 segments and regional tracer uptake was quantitatively analysed. Viability was defined as presence of tracer uptake >50% of peak activity on baseline studies or after reversibility. The percentage of peak activity of^99mTc-tetrofosmin at baseline correlated with that of 201T1 (r=0.82,P <0.001). On baseline^99mTc-tetrofosmin studies, 73 of the 225 segments that were analysed had <50% of peal. activity. Fifteen percent of these segments showed reversibility after nitrate administration, with an increase in^99mTc-tetrofosmin uptake from 40%±9% to 57%±9% of peak activity (P=0.003). All reversible segments after nitrate administration had viability criteria on²⁰¹Tl studies, but 20 segments that were non-viable on^99mTc-tetrofosmin. studies were viable on²⁰¹Tl studies. Using a threshold value of >40% of peak activity, only seven segments remained non-viable on^99mTc-tetrofosmin studies. Overall agreement between^99mTc-tetrofosmin with nitrates and²⁰¹Tl-reinjection regarding the presence of myocardial viability was 90%. Detection of myocardial viability with^99mTc-tetrofosmin. was enhanced after nitrate administration, correlating with viability criteria observed on thallium studies.