Enhanced detection of ischemic but viable myocardium by the reinjection of thallium after stress-redistribution imaging

BACKGROUND

The identification of ischemic but viable myocardium by thallium exercise scintigraphy is often imprecise, since many of the perfusion defects that develop in ischemic myocardium during exercise do not "fill in" on subsequent redistribution images. We hypothesized that a second injection of thallium given after the redistribution images were taken might improve the detection of ischemic but viable myocardium.

METHODS

We studied 100 patients with coronary artery disease, using thallium exercise tomographic imaging and radionuclide angiography. Patients received 2 mCi of thallium intravenously during exercise, redistribution imaging was performed three to four hours later, and a second dose of 1 mCi of thallium was injected at rest immediately thereafter. The three sets of images (stress, redistribution, and reinjection) were then analyzed.

RESULTS

Ninety-two of the 100 patients had exercise-induced perfusion defects. Of the 260 abnormal myocardial regions identified by stress imaging, 85 (33 percent) appeared to be irreversible on redistribution imaging three to four hours later. However, 42 of these apparently irreversible defects (49 percent) demonstrated improved or normal thallium uptake after the second injection of thallium, with an increase in mean regional uptake from 56 +/- 12 percent on redistribution studies to 64 +/- 10 percent on reinjection imaging (P less than 0.001). Twenty patients were restudied three to six months after coronary angioplasty. Of the 15 myocardial regions with defects on redistribution studies that were identified as viable by reinjection studies before angioplasty, 13 (87 percent) had normal thallium uptake and improved regional wall motion after angioplasty. In contrast, all eight regions with persistent defects on reinjection imaging before angioplasty had abnormal thallium uptake and abnormal regional wall motion after angioplasty.

CONCLUSIONS

These data indicate that the reinjection of thallium improves the detection of ischemic myocardium and that myocardial regions with improved thallium uptake on reinjection imaging represent viable but jeopardized myocardium.

[Single-photon emission-computed tomography of the head using labelled amines in visualizing the cerebral microcirculation]

The authors presented clinical material on cerebral hemodynamics in patients with neurological pathology in suspected tumor vascular cerebral diseases and craniocerebral traumas. Investigation of cerebral microcirculation was performed using a multidetector single-photon emission tomograph "Testoscan" (USSR) after iv administration of 99mTc-hexamethylpropilene-amyloxine. This radiopharmaceutical is good for the evaluation of cerebral perfusion and gives a clinician rich information on cerebral microcirculation.

Wiener filtering improves quantification of regional myocardial perfusion with thallium-201 SPECT

Quantitation of myocardial perfusion with thallium-201 (201Tl) SPECT is limited by finite resolution and image noise. This study examined whether Wiener filtering could improve quantitation of the severity of myocardial perfusion deficits. In 19 anesthetized dogs, adjustable stenoses were placed on the left anterior descending (LAD, n = 12) or circumflex (LCx, n = 7) arteries. Thallium-201 SPECT images were acquired during maximal coronary vasodilation with dipyridamole, and simultaneous measurements of myocardial blood flow were made with microspheres. The relationship between SPECT and microsphere flow deficits in the LAD region was significantly better (p less than 0.05) with Wiener filtering (Y = 0.90X + 0.03, r = 0.78) than with conventional Hanning filtering (Y = 0.66X + 0.34, r = 0.61). Similarly, in the LCx region the relationship between SPECT and microsphere perfusion deficits was better (p less than 0.01) with the Wiener filter (Y = 0.91X + 0.07, r = 0.66) than with the Hanning filter (Y = 0.36X + 0.50, r = 0.40). Wiener filtering improves quantitation of the severity of regional myocardial perfusion deficits, allowing better assessment of the functional significance of coronary artery stenoses.

Effect of central cholinergic stimulation on regional cerebral blood flow in Alzheimer disease

Patients with Alzheimer disease (AD) had reduced regional cerebral blood flow (rCBF) in the posterior parietotemporal region compared with controls, as determined with technetium-99m hexamethyl propyleneamine oxime and single photon emission tomography. Central cholinergic stimulation with physostigmine produced a focal increase in rCBF in the posterior parietotemporal region in the patients with AD but not in controls.

[Unfolded map of coronary artery territories by myocardial SPECT]

Coronary artery territories were evaluated precisely by Bull's-eye and unfolded map generated from myocardial SPECT. In addition, unfolded maps including apical information were also developed. The coronary artery territories were determined by 54 cases of typical single vessel disease (more than 75% stenosis) with myocardial infarction and angina pectoris. There were 12 of right coronary artery disease, 24 of left anterior descending coronary artery disease, 5 of diagonal coronary artery disease, and 13 of left circumflex artery disease. Each diseased region was summed and normalized using the standard pattern (21 cases of normal male and 13 cases of normal female). Apical information was simply obtained using the anterior and posterior count from short and long axial image. Then, their data were added to the unfolded map. In conclusion, unfolded map was proven to be useful for the determination of coronary artery territory, since this map expressed the extent and site of myocardial damage precisely compared to Bull's-eye. The unfolded map to contain the apical information was also useful for the evaluation of left anterior descending coronary artery involvement.

[Single-photon emission-computed tomography with the Testascan multidetector gamma tomograph in neurologic practice]

The paper is concerned with the results of single-photon emission tomography and gamma-topography in patients with cerebral tumors, cerebral circulatory disorders and pathology of the liquor system. Tomographic investigation was shown to enhance the accuracy and reliability of the detection of cerebral tumors. Single-photon emission computerized gamma-tomography (SPECT) permitted the detection of structural and morphological cerebral changes in disturbed cerebral circulation of various etiology. SPECT together with computerized tomography and radionuclide cisternography was shown to be an auxiliary method for visualization of the cerebral cisterns. Radionuclide tomographic images as compared to gamma-topographic findings of the brain possessed a high statistical significance and good resolution.

[Clinical evaluation of coronary territory map by using unfolded map of Tl-201 myocardial SPECT]

Coronary territory map was developed on unfolded map of exercise Tl-201 myocardial SPECT. Each coronary territory was determined by summing the each unfolded map of 54 cases of single vessel disease respectively, and standardizing with normal pattern obtained from normal patients. The diagnostic accuracy of coronary territory map to identify the diseased coronary artery was analyzed in 104 clinical cases and was compared with that of planar and SPECT visual diagnosis, simple unfolded map (raw map) and extent & severity map. The results were as follows; 1) Territory map showed excellent diagnostic accuracy in single or double vessel disease, especially in diagnosis of left circumflex coronary artery lesion. 2) In triple vessel disease, the diagnostic accuracy of territory map or other unfolded maps was 30% at best, and was inferior to planar or SPECT visual analysis. The cause of this inferiority seemed that the quantitatively analyzed map had no information about the degree of Tl-uptake into lung or myocardium, which give useful information in visual diagnosis. 3) The diagnostic agreement ratio in two observers was the highest in territory map diagnosis, so that the territory map diagnosis seemed to be the most objective one. 4) The unfolded map diagnosis with apical display obtained from long-axis tomogram was useful to diagnose left anterior descending coronary (LAD) lesion, which improve not only the sensitivity of LAD but also specificity of right coronary artery single vessel disease.

[Lung perfusion scintigraphy by SPECT--new application of bull's eye analysis]

The initial study reports the characteristic performance using lung segmental phantom filled in Tc-99m-pertechnetate. To evaluate the segmental defect in lung perfusion scintigraphy, we applied Bull's-eye analysis in addition to planar image set. Bull's-eye analysis especially facilitated the interpretation in both middle and lower lobes. Subsequently, to evaluate clinical application of Bull's-eye analysis, pulmonary scintigraphy was performed on 10 normal subjects and 60 patients with several pulmonary diseases. Of interest, Bull's-eye analysis, however, encouraged the interpretation in both lower lobes. To calculate the extension and severity of perfusion defect, the present study describes Bull's-eye analysis. Quantitative scoring showed higher in the patients with lung cancer than in those with pulmonary tuberculosis. The present study focus that Bull's-eye analysis can be useful of evaluation for perfusion in the patients with pulmonary a couple of diseases.

Attenuation correction in SPECT based on transmission studies and Monte Carlo simulations of build-up functions

The quantitative information in SPECT images is distorted by photon attenuation and contribution of photons scattered in the object. It is, therefore, important to know the distribution of different attenuating tissues in order to be able to perform a proper attenuation correction. A correction method, based on correcting one pixel at a time by using density maps and build-up functions, has been developed. The density map has been produced by transmission measurements of the object using an external, solid 57Co flood source mounted on the scintillation camera head. The outline of the object is accurately defined by the map since the density values outside the object are very close to zero. The build-up of photons scattered in the object has been simulated by a Monte-Carlo code. SPECT-studies with 99mTc, 201T1 and 111In line sources in different parts of a non homogeneous Alderson phantom have been performed. The emission images have been corrected for photon attenuation using the measured density maps and the simulated build-up functions. The results show that quantitative measurements of the radioactivity in nonhomogeneous area can be accomplished to within +/- 10% for different radionuclides by using the attenuation correction described.

[An improvement on the two-dimensional convolution method of image reconstruction and its application to SPECT]

In single-photon emission computed tomography (SPECT) and X-ray CT one-dimensional (1-D) convolution method is used for their image reconstruction from projections. The method makes a 1-D convolution filtering on projection data with a 1-D filter in the space domain, and back projects the filtered data for reconstruction. Images can also be reconstructed by first forming the 2-D backprojection images from projections and then convoluting them with a 2-D space-domain filter. This is the reconstruction by the 2-D convolution method, and it has the opposite reconstruction process to the 1-D convolution method. Since the 2-D convolution method is inferior to the 1-D convolution method in speed in reconstruction, it has no practical use. In the actual reconstruction by the 2-D convolution method, convolution is made on a finite plane which is called convolution window. A convolution window of size N X N needs a 2-D discrete filter of the same size. If better reconstructions are achieved with small convolution windows, the reconstruction time for the 2-D convolution method can be reduced. For this purpose, 2-D filters of a simple function form are proposed which can give good reconstructions with small convolution windows. They are here defined on a finite plane, depending on the window size used, although a filter function is usually defined on the infinite plane. They are however set so that they better approximate the property of a 2-D filter function defined on the infinite plane. Filters of size N X N are thus determined. Their value varies with window size. The filters are applied to image reconstructions of SPECT.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of fast data acquisition method with Tc-99m HMPAO brain SPECT in patients with acute stroke

The first data acquisition method for Tc-99m hexamethylpropyleneamineoxime (Tc-99m HMPAO) brain SPECT was used in two patients with acute stroke 5 and 8 hours after the event. In one patient Tc-99m HMPAO fast SPECT showed perfusion defects before the same was manifested on CT. In the other patient, Tc-99m HMPAO fast SPECT showed larger defects than the edema seen on CT. The Tc-99m HMPAO fast SPECT might be feasible for the evaluation of acute stroke patients. Since the time required for fast SPECT is much shorter than usual SPECT, it appears to be more suitable for some patients with acute stroke who are brought to the hospital in a very critical condition.

Estimation of geometrical parameters and collimator evaluation for cone beam tomography

A method is presented for estimating the geometrical parameters for a cone beam detector geometry from the coordinates of the centroid of a projected point source sampled over 360 degrees. Nonlinear expressions are derived for the coordinates of the centroids in terms of the geometrical parameters which include: the two-dimensional coordinates of the projection of the center of rotation onto the detector image plane; the focal length; the distance from the focal point to the center of rotation; and the spatial coordinates of the point source itself. Experimental data were obtained using a rotating gamma camera with a symmetrically converging collimator. The Marquardt algorithm was used to estimate the parameters for this particular cone beam geometry. The method was able to estimate the geometrical parameters and evaluate the accuracy of the collimator construction.

Quantitative SPECT by attenuation correction of the projection set using transmission data: evaluation of a method

A method for measuring attenuation coefficients in single-photon emission tomography (SPECT) is described and evaluated, together with a method for attenuation correction using these measured attenuation coefficients. Build-up, caused by scattered photons, is corrected for by a simple substitution in the algorithms. Transmission studies are performed with a 99mTc- or 57Co flood source, and emission phantom studies with 99mTc line sources. The method is evaluated with variable but well-defined phantoms. The result is accurate attenuation coefficients for different densities, dimensions and geometries, and an accuracy of corrected emission activities of better than +/- 10% in most cases. The present limitations of the method for attenuation correction are discussed.

High reproducibility of regional abnormalities on interictal 123I-IMP SPECT brain scans in adults with partial epilepsy

The reproducibility of two N-isopropyl-(iodine 123) p-iodoamphetamine (123I-IMP single photon emission computed tomography (SPECT) scans both taken during interictal periods was studied in 13 adult patients with partial epilepsy who had normal CT scans. The frequency of the seizures and the nature of the ictal symptoms were virtually unchanged during the interval between the two SPECT scans performed in each case. In 8 (72.7%) of 11 patients who had abnormal images consisting of focal hypofixation images of 123I-IMP, i.e. zones of decreased regional cerebral blood flow on the first scans, complete or partial regional reproduction of the SPECT abnormalities was observed. This high reproducibility supports the usefulness of SPECT scans in the regional diagnosis of epileptic foci.

SPECT in the presurgical evaluation of patients with temporal lobe epilepsy--a preliminary report

Twenty-eight patients with drug resistant temporal lobe epilepsy (DRTLE) were studied using single photon emission computed tomography (SPECT) using xenon-133 inhalation and Tc99m-d, 1-HMPAO with TOMOMATIC 64 as part of a presurgical evaluation programme. The visually evaluated flow-images were studied after blinding and the results subsequently compared to the EEG, MRI and CT scanning studies. In 24 patients a significant low flow region was seen in one temporal lobe. The SPECT result corresponded to the EEG findings in all but 6 patients. In 2 of these patients no side localization was indicated by EEG, while in four patients the EEG suggested that the opposite side was epileptogenic. Ictal SPECT and MRI/CT agreed with the resting SPECT study in three patients, while one patient has remained undiagnosed with respect to side-localization. In 14 patients discordance between SPECT and the CT scan was observed, but in 11 of these patients the SPECT study correlated with the other focal diagnostic tools. In 11 of the 21 patients studied by MRI, the results corresponded to SPECT; in 7 of the 10 which did not correspond, ictal studies of EEG and SPECT defined the side, in four of these 7 patients. Using the neuroimaging tools in concert 16 patients have been selected for surgery. All patients have benefited from surgery. These preliminary results correspond favourably with earlier studies comparing SPECT and PET with CT, MR and EEG.

Regional cerebral blood flow study with 99mTc-hexamethyl-propyleneamine oxime single photon emission computed tomography in Alzheimer's and multi-infarct dementia

Thirty-four demented patients, 19 with Alzheimer's and 15 with multi-infarct dementia, were studied using single photon emission computed tomography, and 99mTc-hexamethyl-propylenemine oxime as a tracer of regional cerebral perfusion. Tracer activity ratios, determined in cortical and subcortical regions, were compared with those of 11 age-matched controls. In both groups of demented patients, most of the cortical regions showed significant declines in tracer uptake from control values, with the greatest reductions in the parietal cortex. Significantly lower parietal indexes were found in the Alzheimer's patient group as compared both to the control values and to the group of multi-infarct dementia patients. A positive correlation was found between the magnitude of the parietal deficits and the severity of dementia.

Three-dimensional alignment of functional and morphological tomograms

A method has been developed to create corresponding brain slices from morphological [CT, magnetic resonance (MR)] and functional [positron emission tomography (PET), single photon emission computed tomography] tomographic studies in individual patients. It does not require special headholders or definition of specific landmarks and is fully retrospective. Three-dimensional image registration in corresponding orientation is achieved by linear interpolation of original slices and a variety of interactively controlled video display options. These include simultaneous display of multiple slices and brain cuts in all three dimensions for comparison of positioning. Brain contours in one imaging modality may be enhanced by appropriate filtering and superimposed onto reference images of another modality. Matching accuracy depends on image resolution; misalignment of 4 mm was detected unambiguously in sample studies (fluoro-2-deoxy-D-glucose PET matched with MR). The technique is equally well applicable to normals and to patients with structural brain lesions. Additional options for shaded surface display enhance the power to identify neuroanatomical structures in functional image analysis. As demonstrated in the example of MR-guided PET, this modeling procedure can be successfully used for identification of brain structures on functional images, even in patients with pathologically altered brain morphology.

Error of uptake in dual energy acquisition with 201Tl and 123I labeled radiopharmaceuticals

In myocardial scintigraphy, simultaneous injection of two radionuclides and dual energy acquisition are potentially useful in the assessment of regional perfusion and metabolism. The feasibility of dual radionuclide study with 201Tl and 123I labeled radiopharmaceuticals (meta-iodobenzylguanidine I 123, in this study) was investigated in phantoms and patients. The crosstalk of one radionuclide to the other pulse height window was defined as the ratio of the 201Tl count in the 123I and 201Tl windows, R[I/Tl], and the ratio of the 123I count in the 201Tl and 123I windows, R[Tl/I]. The ratios were determined in planar images and SPECT studies. In clinical studies with whole body scintigraphy (n = 8), the value of R differed significantly in various organs. In the SPECT study (n = 13), R was not uniform and varied with time and location, resulting in significant errors in uptake and regional count ratio. Thus, dual energy acquisition with 201Tl and 123I labeled radiopharmaceuticals is generally not recommended because of varying amounts of crosstalk interference. Possible solutions to this problem are discussed. The feasibility of dual radionuclide study must be confirmed in human as well as in phantom studies.

Imaging of propagated sites of epileptic discharges in repeated 123I-IMP SPECT scans

Single-photon emission computed tomographic (SPECT) brain scans with N-isopropyl-(iodine-123-p-iodoamphetamine (123I-IMP) were performed twice at an interval of about 2.5 years in the interictal period in an adult patient with occipital-lobe epilepsy. The first SPECT scan showed an abnormal image of decreased 123I-IMP uptake in the right occipital lobe. This abnormal image was regarded as the primary focus of his epilepsy on the basis of its regional agreement with right-occipital spikes consistently seen in interictal electroencephalographic recordings throughout his clinical history. In the second scan, he showed multiple abnormal images of decreased uptake in the right frontotemporal lobes and left occipital lobe together with the right occipital lobe. These additional abnormal images were considered to be propagated sites of epileptic discharges.

Dual isotope thallium and indium antimyosin SPECT imaging to identify acute infarct patients at further ischemic risk

Forty-two patients (28 men and 14 women) with acute myocardial infarction (35 Q, seven non-Q wave) were injected with 2.0 mCi indium 111-labeled antimyosin (AM) monoclonal antibody (111In AM) within 48 hours of the onset of chest pain. Forty-eight hours later (72-96 hours after onset of chest pain), patients were injected with 2.2 mCi thallium 201, and two sets of single-photon emission computed tomography (SPECT) images were obtained simultaneously using dual energy windows set for the 247 keV indium photopeak and the 70 keV thallium peak. Seventeen patients had repeat scans at 4 hours. 111In AM uptake and 201Tl defects were localized to one or more of 24 coronal and sagittal segments. Scans with only 201Tl defects and corresponding 111In AM uptake were classified as matches; scans with unmatched 201Tl defects in addition to matching regions corresponding to electrocardiographic infarct location were classified as mismatches; and scans with 201Tl and 111In AM uptake in the same segments were classified as overlap. Scan patterns were correlated with clinical evidence for residual ischemia occurring within 6 weeks of infarct and including infarct extension, recurrent angina, and positive predischarge low-level or 6-week symptom-limited stress tests and with coronary anatomy. Fourteen patients had only matching patterns (group 1), 23 had mismatches (group 2), and five had 201Tl-111In overlap as the predominant pattern. None of the patients in group 1 had previous myocardial infarction; in each, the matched area corresponded to the Q wave location on electrocardiogram, and none had further in-hospital ischemic events or positive stress tests.(ABSTRACT TRUNCATED AT 250 WORDS)

[Clinical evaluation of Tl-201 ECG-gated myocardial SPECT--comparison with ECG-gated blood pool SPECT]

In order to evaluate the clinical usefulness of the Tl-201 ECG-gated myocardial single photon emission computed tomography (SPECT), we compared the wall motion and the grade of the Tl-201 uptake of the ECG-gated myocardial SPECT with the wall motion of the ECG-gated blood pool SPECT. Materials were 87 patients of 50 old myocardial infarctions (OMIs), 19 hypertrophic cardiomyopathies (HCMs), 2 dilated cardiomyopathies (DCMs) and 16 others. After intravenous injection of 111-185 MBq (3-5 mCi) of Tl-201 at rest, the projection data were acquired using a rotating gamma-camera through 180 degrees, from RAO 45 degrees in 24 directions, each of which consisted of 80-100 beats. For the reconstruction of ED, ES and non-gated images, R-R interval was divided into about 20 (18-22) fractions. In 348 regions of interest (anterior, septal, lateral and inferior wall) in 87 cases, wall motion and the Tl-201 uptake were evaluated to three grades (normal, hypokinesis and akinesis; normal, low and defect, respectively), which were compared with the wall motion of the ECG-gated blood pool SPECT. The wall motion and the grade of the Tl-201 uptake of the ECG-gated myocardial SPECT correlated well with the wall motion of the ECG-gated blood pool SPECT (96.6% and 87.9%, respectively). In conclusion, the ECG-gated myocardial SPECT can provide clear perfusion images and is a very useful diagnostic strategy to evaluate the regional wall motion and perfusion simultaneously.

Routine 18F-2-deoxy-2-fluoro-D-glucose (18F-FDG) myocardial tomography using a normal large field of view gamma-camera

There is a recent need to study glucose metabolism of the heart in ischemic, as well as in "hibernating or stunned" myocardium, and compare it with that in perfusion studies. In non-positron emission tomography centers, positron imaging is possible with a standard Anger-type camera if proper collimation and adequate shielding of the camera crystal can be achieved. For the study with fast-decaying isotopes, seven-pinhole tomography (7PHT), a limited-angle method designed for transaxial tomography of the left ventricle using a nonrotating camera, is well suited, because projections are acquired simultaneously. Individual adjustment (patient supine) of the camera's view axis (CAx) with the left ventricular axis (LVAx) gives excellent results: sensitivity for CHD 82%, specificity 72% in a prospective 201TI study (48 patients, x-ray coronarography as reference). Good alignment of CAx with LVAx is also achieved with the patient prone in LAO in a hammock above the camera surface. In this setting additional lead shielding of the camera is possible using a table reinforced with 5 cm of lead with a central hole for the 7PH-collimator, which has a special lead inlay. This allows utilization of the 511 KeV emitter 18F-FDG, which with a half-life of 109 minutes, can be transported a reasonable distance from the production site. System sensitivity and resolution for 18F was found comparable to 201Tl, 99mTc, and 123I using a phantom. First clinical examinations after 201Tl stress/redistribution studies showed increased 18F-FDG uptake in ischemic heart segments, as well as in "hibernating" nonperfused or "stunned" myocardium.

[Lung perfusion scintigraphy by SPECT--new application of Bull's eye analysis]

The present study reports the characteristic performance using lung segmental phantom filled in Tc-99m-pertechnetate. To evaluate the segmental defect in lung perfusion scintigraphy, we applied Bull's eye analysis in addition to planar image set. Bull's eye analysis especially facilitated the interpretation in both middle and lower lobes.

[Clinical significance of the technetium-99m/thallium-201 overlap in acute myocardial infarction]

The region of overlap of thallium-201 (Tl) and technetium-99m pyrophosphate (Tc) was evaluated as a scintigraphic prognosticator of future necrosis. Serial time courses of myocardial perfusion according to Tl and left ventricular wall motion evaluated by two-dimensional echocardiography (2D echo) were used in 22 patients. In all, dual energy emission computed tomography (dual-SPECT) showed the Tl/Tc overlap on identical slices on the third post-infarction day. According to the results of dual-SPECT, the patients were categorized in three groups: nine with large Tl/Tc overlap (group A); five with small Tc accumulation and small Tl/Tc overlap (group B); and eight with large Tl defect and Tc accumulation, which are concordant with each other (group C). Tl-201 SPECT and 2D echo were attempted serially on the 1st and 2nd days, the 7th-10th days and the 28th-30th days. To estimate infarct size with Tl-201 SPECT, we measured pixel counts of eight short-axis images with the 40% cut-off level and computed "% defect". To evaluate the viability of the myocardium, "% Tl uptake" was computed from the ROIs both in the centers of the infarct areas and their border zones. 2D echoes of the left ventricular short axis at the chordae tendineae level were recorded to identify the time course of percent fractional area change (% FAC) of the ischemic left ventricular wall. The scintigraphic results were compared with the serial changes of regional ejection fraction in the areas of infarcts and ischemic lesions. The % defect remained unchanged in group C (29.2 +/- 11.5----25.7 +/- 8.3%); whereas those of groups A and B decreased significantly (21.2 +/- 11.3----9.9 +/- 6.3%, 13.8 +/- 2.6----5.4 +/- 2.9%, respectively). In groups A and B, % FAC improved significantly in the centers of the infarct areas and the border zones, but not in group C. Exercise-induced ischemia determined by redistribution of Tl at the chronic phase was observed more frequently in groups A and B than in group C. These findings indicated that more myocardium can be saved from necrosis in group A than in group C. In conclusion, it is suggested that there is considerable viable myocardium in patients with large Tl/Tc overlap on dual-SPECT.

[Radioanatomy of cerebral perfusion in single-photon emission-computed tomography using 99mTc-labelled amines]

A study was made of the cerebral hemodynamics by assessing the distribution in single-photon emission computerized tomography with 99mTc-hexamethyl-propyleneminoxyne in health using a Testascan in 9 standard slices. The whole set of tomographic slices was conventionally divided into 3 levels. For better orientation in gamma-tomographic images, pictures were presented where in addition to scintigrams a morphological scheme of the cerebral parts with the marked parts perfused by cerebral arteries, was given.

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 super-imposition 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.

Characterization of technetium-99m-L,L-ECD for brain perfusion imaging, Part 2: Biodistribution and brain imaging in humans

The safety, biodistribution and kinetics of a new perfusion imaging agent [99mTc-L,L]-ethyl cysteinate dimer (ECD) was evaluated in normal volunteers. Technetium-99m-L,L-ECD is a neutral, lipophilic complex, which is radiochemically pure and stable. Twelve healthy adults were injected with 25-30 mCi of 99mTc-L,L-ECD and imaged periodically for up to 24 hr. Planar imaging showed rapid brain uptake with a peak concentration of 4.9% injected dose and very slow brain washout (approximately 6% per hour during the first 6 hr). Repeat or dynamic tomographic imaging of the brain using either a rotating gamma camera or a multidetector system was performed up to 6 hr postinjection. The distribution of 99mTc-L,L-ECD in the brain did not change and was similar to the pattern seen with other perfusion agents. Background facial areas and lungs cleared rapidly. Peak blood activity was below 10% injected dose at all times and 99mTc-L,L-ECD cleared rapidly through the kidneys. Vital signs, blood and urine chemistries were normal in all volunteers and no adverse reactions were noted. These results suggest that 99mTc-L,L-ECD should be useful for routine assessment of cerebral perfusion in humans.

Dynamic geometric mean studies using a single headed rotating gamma camera

A technique for acquiring dynamic geometric mean studies utilizing a single-headed rotating gamma camera has been developed. The camera head is repeatedly rotated between opposed views under computer control. A single data set results, from which a dynamic sequence of geometric mean images can be produced. Software has been developed to accomplish data acquisition and the reformatting required. The accuracy of the geometric mean data formed using this technique has been studied experimentally, and compared with results obtained from anterior and posterior sequences. In a simple clearance experiment of a 1-I volume with a known clearance of 20 ml.min-1, the geometric mean data resulted in estimates of volume remaining in the container with a mean error or +2.0 ml (s.d. = 5.7 ml, range -4.5 +/- 15.3 ml), while the anterior and posterior images yielded volume estimates with mean errors of -10.1 ml (s.d. = 16.6 ml, range -47.4 +/- 10.5 ml) and +35.5 ml (s.d. = 22.6 ml, range -3.2 +/- 51.6, ml), respectively. The technique is easy to implement and does not require modification of existing hardware. An application of the technique to a clinical study of gastric emptying is also included.

A new scanning method for thallium-201 myocardial SPECT: semidecubital position method

The authors have developed a new scanning method for Tl-201 myocardial SPECT using a rotating gamma camera with 180-degree data collection. This requires a new type of imaging table on which the patient is placed in a 50-degree right semidecubital position to allow close proximity to the camera-collimator system. Using this method, attenuation by the imaging table is completely avoidable because the projected views in the left oblique directions are not obstructed by the table. In addition, the radius of camera rotation is about 25% shorter than in the conventional method. Phantom and 16 clinical studies were performed to compare the performance of conventional and semidecubital position methods. In phantom studies, tomographic images produced using the new method showed better lesion contrast and more counts in the posteroinferior wall of the heart than those produced using the conventional method. Clinically, 12 of the 16 studies showed more counts in the posteroinferior wall of the heart with the semidecubital position method than with the conventional method. The semidecubital position method is useful for Tl-201 myocardial SPECT, especially for evaluation of posteroinferior wall hypoperfusion.

Technical introduction to nuclear imaging

It is very important to pay attention to technical detail when acquiring nuclear scans of the heart. It must be remembered that not only is the heart a three dimensional structure, which imposes its own limitations on the interpretation of information represented as two dimensional images, but the organ also moves which will in turn degrade static images. Dynamic studies of left ventricular function must be able to resolve the rapidly changing events of the cardiac cycle which makes specific technical demands upon the imaging equipment and computer system used. In spite of these potential drawbacks, both static and dynamic imaging of the heart using radiopharmaceuticals are widely used in a clinical and research environment. In this article some of the technical considerations will be covered as they apply to both the commonly used clinical applications of nuclear cardiology and some of the newer but potentially exciting techniques will also be covered briefly.

Investigation of causes of geometric distortion in 180 degrees and 360 degrees angular sampling in SPECT

To investigate geometric distortion when 180 degrees or 360 degrees angular sampling techniques are used in single photon emission computed tomography (SPECT), a study of point sources imaged at different positions in a water filled cylindrical phantom, and reconstructed using filtered back projection, was conducted. A simulation study, based upon a serial model of the system point spread function (PSF), was used to investigate the contributions of attenuation, spatial resolution and scatter on distortion of the reconstructed PSFs. To study the geometric distortion in transverse (x-y plane), coronal (x-z plane), and sagittal (y-z plane) sections, the ratios of the full widths at half maximum (FWHM) and full widths at tenth maximum (FWTM) in the x/y, x/z, and y/z directions were calculated for the real and simulated PSFs. These results showed that, in an attenuating medium, there is more distortion of point sources into ovals for 180 degrees than for 360 degrees sampling. The simulation study indicated that the primary cause of geometrical distortion in SPECT studies, is the inconsistency of projections due to variable attenuation and spatial resolution. The impact of scatter on geometric distortion was small as measured by the ratios of FWHMs and FWTMs for PSFs. Attenuation correction applied to acquired PSFs significantly reduced geometric distortion in both 180 degrees and 360 degrees studies. To investigate distortion in extended objects, an Iowa heart phantom was placed inside an Alderson body phantom and 201Tl heart SPECT studies acquired. The phantom images confirmed the conclusion that in transverse sections of 360 degrees studies with arithmetic averaging of opposite views, geometric distortion is reduced compared to 180 degrees. The coronal and sagittal sections were equally distorted in both, the 180 degrees and 360 degrees studies, and the 180 degrees studies yielded better contrast.

"Upward creep" of the heart: a frequent source of false-positive reversible defects during thallium-201 stress-redistribution SPECT

A new cause of artifactual 201Tl defects on single photon emission computed tomography (SPECT) termed "upward creep" of the heart is described. In 102 consecutive patients undergoing 201Tl SPECT, 30 (29%) demonstrated upward creep defined by an upward movement of the heart of greater than or equal to 2 pixels during acquisition. In 45 consecutive patients with a less than 5% likelihood of coronary artery disease, 17 (38%) had upward creep. Of these nine had reversible 201Tl defects localized to the inferior and basal inferoseptal walls, while none of the 28 without upward creep had defects. The 17 low likelihood patients with upward creep had longer exercise duration and higher peak heart rate than those without upward creep. In five additional low likelihood patients with upward creep in whom imaging was immediately repeated, the upward creep pattern disappeared on the repeated images. After we changed our test protocol to begin imaging 15 min postexercise, only five (14%) of 36 low likelihood patients tested demonstrated upward creep. Upward creep is probably related to a transient increase in mean total lung volume early following exhaustive exercise, resulting in a mean lower position of the diaphragm (and thus the heart) at the beginning of imaging. The frequency of this source of false-positive 201Tl studies can be reduced by delaying SPECT acquisition until 15 min postexercise.

Perspectives on imaging modalities

In the comparison of various techniques it is important to analyze what is known about the physical possibilities of a particular technique for making a specific measurement. X-ray CT, ultrasound, and emission methods with radionuclides do not measure chemical composition. NMR can uniquely measure chemical composition. Unfortunately in the measurement of chemical composition, NMR is insensitive, thus large volumes of tissue must be selected by the NMR spectroscopic experiment for a reliable measurement. Measurements that rely on tissue physical differences to detect surfaces and motion include rapid x-ray imaging and ultrasound. For these reasons they have some attributes for particular types of studies that are superior to emission tomography and NMR. However, in the past few years, improvements in the NMR technology have led to the ability to acquire images representing only 30 sec of time in 3-dimensional studies of the beating human heart. It was believed until recently that anatomical resolution of PET was so poor that other imaging modalities would have to be used to delineate the specific region from which the PET information was coming, particularly in studies of the brain. However, in the past year it has been demonstrated that PET can acquire high resolution images of the CNS cortical ribbon at 2.5 mm or better.(ABSTRACT TRUNCATED AT 250 WORDS)

[New color imaging of [99mTc]-pyrophosphate and [201Tl]-chloride dual isotope single photon emission computed tomography in acute myocarditis]

[99mTc]-pyrophosphate (PYP) and [201Tl]-chloride dual isotope single photon emission computed tomography (SPECT) is now available to detect the site and extent of acute myocardial infarction. In inflammatory myocardial disease, [99mTc]PYP makes hot image on damaged area. We performed dual isotope SPECT of [99mTc]PYP and [201Tl]Cl in two patients with acute myocarditis and severe rhythm disturbance to evaluate the severity of inflammation. Myocardial damage was estimated by [201Tl] perfusion coloring blue and myocardial inflammation was estimated by [99mTc]PYP uptake coloring red. The overlap display of both images made it clear to detect spatial extent of myocardial inflammation. Using this technique, we expect to estimate the severity of myocarditis and to make a decision of therapeutic plan.

Cerebral correlates of imagining colours, faces and a map--I. SPECT of regional cerebral blood flow

The distribution of regional cerebral blood flow (rCBF) was assessed by single photon emission computerized tomography (SPECT) in subjects during a resting state and during imagining either colours or faces or a route on a map. Twelve out of 30 subjects reported the spontaneous occurrence of mental visual images during the resting state. In these subjects flow in both orbitofrontal regions was higher than in those subjects who had not experienced spontaneous imagery. Voluntary imagery led to an increase of regional flow indices in basal temporal regions of both hemispheres and to a rightwards shift of global hemispheric asymmetry. The local changes were distinctly more marked with faces than with any of the other two stimuli. Imagining faces was also the only condition that led to an increase of activity in the left inferior occipital region which has been suggested by previous studies as being a crucial area for visual imagery. It is concluded that the observed differences of rCBF patterns between imagery conditions are related to the amount of information conveyed by the mental image. In contrast to the results of a companion study on DC-shifts accompanying imagery there was no effect of the visual versus spatial character of the images.