Peter H. Jarritt

A comparison of three radionuclide myocardial perfusion tracers in clinical practice: the ROBUST study.

Abstract. There are no large studies available to guide the selection of thallium (Tl), methoxyisobutylisonitrile (MIBI) or tetrofosmin (Tf) for myocardial perfusion imaging. Our objective was to compare the technical and clinical performance of the three in routine clinical practice. We randomised 2,560 patients to receive Tl, MIBI or Tf. A 1-day stress/rest protocol was used for MIBI and Tf. Tracer uptake was scored using a 17-segment model, quality and artefact scores were assigned, and ratios of heart (H), liver (L), subdiaphragmatic (S) and lung activity were measured. Mean quality scores (stress/rest) were Tl 2.13/2.16, MIBI 2.18/2.39, Tf 2.18/2.42 (P=ns stress and <0.00001 rest). For attenuation artefact, Tl>MIBI=Tf (P<0.05) and for low-count artefact Tl>MIBI>Tf (P<0.001). For H/S, Tl>MIBI=Tf, for H/L Tl>MIBI=Tf, and for H/lung Tl<MIBI=Tf. Stress defects in the patients with reversible or mixed perfusion defects were more severe for Tl than for the other tracers (mean summed score out of 68: Tl 52.3, MIBI 55.7, Tf 54.4, P<0.01), but mean rest scores were more similar (Tl 58.7, MIBI 60.7, Tf 59.4, P=0.02). In the subset of 137 patients undergoing diagnostic perfusion studies without prior infarction, angiography or revascularisation, overall sensitivity for the detection of coronary disease defined by subsequent angiography was 91% with a specificity of 87%. There were no significant differences between the tracers with regard to sensitivity and specificity. In conclusion: There are technical differences between the tracers. Overall image quality score is superior using technetium, with less low-count artefact and less attenuation. Stress defect depth and extent are slightly greater using thallium, with no difference between MIBI and tetrofosmin. All three tracers perform well in clinical terms, with high sensitivity and specificity for angiographic stenosis and no differences in accuracy between the tracers.

The in vivo distribution of 99Tcm-HM-PAO in normal man

The distribution of 99Tcm-HM-PAO is described in normal man. Since our initial report on the clinical potential of this new radiopharmaceutical in 1984, a number of clinical trials are in progress worldwide. As the tracer has been designed to enable the in vivo assessment of the distribution of cerebral blood flow in man, significant interest in this new 99Tcm-labelled compound can be detected not only in the nuclear medicine practice in general, but in the more specialist areas of medicine such as neurology and psychiatry. In this paper we report findings which should aid in the evaluation of this compound in normal individuals.

Neuroactivation and neuroimaging with SPET

This book describes the application of single photon emission tomography (SPET) to neuroactivation imaging in particular and neuroimaging in general. Protocols for SPET, neuroactivation and neuroimaging are described in detail and results are given and discussed on the basis of clinical material and case histories. Normal functional anatomy is correlated with data from MRI. High resolution cerebral blood flow (CBF) imaging is described with the use of SPET technology. Split dose CBF imaging is also mentioned, for activation studies in a variety of normal and diseased states which include the dementias (AIDS, Alzheimers disease and multi-infarction dementia), cerebrovascular disease, depression, schizophrenia, obsessive compulsive disorders, movement disorders (Parkinsons disease, Gilles de la Tourette syndrome, Huntingdons chorea, Sydenhams chorea), epilepsy and tumours. Examples of motor, frontal and visual activation studies are also given.

Physical assessment of the GE/CGR Neurocam and comparison with a single rotating gamma-camera.

The GE/CGR Neurocam is a triple-headed single photon emission tomography (SPET) system dedicated to multi-slice brain tomography. We have assessed its physical performance in terms of sensitivity and resolution, and its clinical efficacy in comparison with a modern, single rotating gamma-camera (GE 400XCT). Using a water-filled cylinder containing technetium-99m, the tomographic volume sensitivity of the Neurocam was 30.0 and 50.7 kcps/MBq · ml · cm for the high-resolution (HR) and general-purpose (GP) collimators, respectively; the corresponding values for the single rotating camera were 7.6 and 12.8 kcps/(MBq/ml)/cm. Tomographic resolution was measured in air and in water. In air, the Neurocam resolution at the cente of the field-of-view (FOV) is 9.0 and 10.7 mm full width at half-maximum (FWHM) with the HR and GP collimators, respectively, and is isotropic in the three orthogonal planes; the resolution of the GE 400XCT with 13 cm radius of rotation is 10.3 and 11.7 mm, respectively. For the Neurocam with the HR collimator, the transaxial FWHM values in water were 9.7 mm at the centre and 9.5 mm radial (6.6 mm tangential) at 8 cm from the centre. The physical characteristics of the Neurocam enable the routine acquisition of brain perfusion data with technetium-99m hexamethyl-propylene amine oxime (99mTc-HMPAO) in about 14 min, yielding better image quality than with a single rotating camera in 40 min.

Intracellular localization of 99Tcm-d,l-HMPAO and 201Tl-DDC in rat brain.

The intracellular localization and relative distribution of 99Tcm-hexamethylpropyleneamine-oxime (99Tcm-d, l-HMPAO) and 201Tl-diethyldithiocarbamate (201Tl-DDC), which have been used to assess regional cerebral blood flow (rCBF) in man, were investigated in rat brain. 99Tcm-d, l-HMPAO was found attached mainly to cell organelles whilst 201Tl-DDC was localized mainly in free state in the cytosolic fraction. Isolation of neuronal and glial nuclei showed that there is higher uptake of 99Tcm-d, l-HMPAO in neuronal nuclei than in glial nuclei for all the different regions of the rat brain investigated. These data demonstrate a different subcellular localization of the two lipophilic agents studied. In view of their proposed clinical utility, this difference merits further investigation.

Transmission scanning for attenuation correction of myocardial 201Tl images in obese patients

For attenuation correction (AC) of 201Tl myocardial perfusion images, an accurate attenuation map is required. This study assessed whether prolonged transmission scanning is required in obese compared to normal-sized patients. Twenty-nine obese patients (mean body mass index 33 kg m-2) underwent sequential emission/transmission imaging for AC using an L-shaped, dual-headed gamma camera fitted with two 153Gd scanning line sources. Transmission data were acquired for 5 s per view (scan time for normal-sized patients) and for 10 s per view and used to reconstruct individual attenuation maps. Emission data were reconstructed using each attenuation map in turn to produce attenuation-corrected images (AC5 and AC10). Tracer distribution in the AC5 and AC10 images was compared by two observers blinded to study type. For each data set, count density was measured in 17 segments of a polar plot and segmental uptake expressed relative to study maximum. Although myocardial count density was low on the 5 s per view transmission images (0.5-13.0 and 3.0-14.0 counts per pixel in the anteroposterior and lateral projections respectively), no significant differences in tracer distribution were seen between the AC5 and AC10 images and these were reported identically. In addition, the mean segmental relative uptake values were similar (P > 0.05) for corresponding segments of the AC5 and AC10 images. We conclude that prolonged transmission scanning is not required in obese compared to normal-sized patients. The transmission scanning protocol used in normal-sized patients is applicable across a wide patient weight range.

201Tl myocardial perfusion SPET: adenosine alone or combined with dynamic exercise

&NA; 201T1 myocardial perfusion single photon emission tomography (SPET) with pharmacological coronary vasodilatation using adenosine is now often used in the investigation of a patient with ischaemic heart disease (IHD). In this study, we present data from two groups of patients. Group A (n=40) experienced 201T1 SPET with adenosine only as the pharmacological stress test, using an infusion rate of 140 μg kg−1 min−1. Group B patients (n=50) had the same test combined with low‐level dynamic exercise. The side effects were noted for both groups and 201T1 SPET studies were acquired for stress and redistribution images. There was a lesser degree of non‐cardiac side effects in patients of group B. There was a significant difference in the haemodynamic parameters between the two groups. There was no significant difference in overall sensitivity (87% versus 90%) and specificity (84% versus 88%) in the detection of IHD between the two groups. In conclusion, addition of low‐level dynamic exercise with adenosine is to be preferred to adenosine infusion alone, as this protocol is better tolerated and may enhance the detection of right coronary artery disease (sensitivity=82% versus 90%, n.s.).

Emission tomography in embolic lung disease: angiographic correlations.

The data from 84 patients with suspected embolic lung disease who underwent radionuclide section scanning of the chest is reported. All underwent additional conventional planar imaging; specific angiographic evidence of embolic disease was available in 12 cases. A good correlation between the section scans and angiography was obtained. Greater sensitivity in lesion detection was obtained by multiplane section imaging, which should reduce the number of diagnostic uncertainties in embolic lung disease.

High-resolution renal SPECT in eight minutes using a multi-detector gamma camera

Planar renal scintigraphy with Tc-99m DMSA has become established as a standard diagnostic test to determine if a kidney has been scarred by infection. It has been suggested that high resolution SPECT may improve the sensitivity of detection of renal scars. To determine if it is possible to produce good quality renal SPECT with a short acquisition time, 10 adults were examined with a new multi-detector gamma camera using 8 minute, 16 minute, and 32 minute acquisitions. The number of defects seen (N = 16) with an 8 minute acquisition was not significantly different from the defects (N = 15) seen using a 16 minute and a 32 minute acquisition. In adults when Imaging with a multi-detector gamma camera there was no clinical advantage in using an acquisition of longer than 8 minutes.

Clinical experience with a multidetector SPET system (Toshiba GCA-9300A).

&NA; The clinical experience with the Toshiba GCA‐9300A single photon emission tomography (SPET) system is discussed along with typical acquisition protocols for various SPET studies. The system was used to perform SPET studies in normals and in a variety of brain and body disorders. Its three Anger‐type gamma cameras forming a triangular aperture offer a substantial increase in sensitivity compared to a single rotating gamma camera. This has allowed the routine use of lead fanbeam super high‐resolution collimators (SHR FB) for 99Tcm‐hexamethylpropyleneamine oxime (HMPAO) brain SPET studies and high‐resolution parallel‐hole collimators (HR PH) for cardiac and other body studies. The resulting improvement in spatial resolution coupled with the ease of patient positioning and the greater patient throughput compared to a conventional tomographic gamma camera, will enhance the role of brain and body SPET for both routine and research purposes.