Quantitative 177Lu SPECT imaging using advanced correction algorithms in non-reference geometry.

Peptide receptor therapy with 177Lu-labelled somatostatin analogues is a promising tool in the management of patients with inoperable or metastasized neuroendocrine tumours. The aim of this work was to perform accurate activity quantification of 177Lu in complex anthropomorphic geometry using advanced correction algorithms. Acquisitions were performed on the higher 177Lu photopeak (208keV) using a Philips IRIX gamma camera provided with medium-energy collimators. System calibration was performed using a 16mL Jaszczak sphere surrounded by non-radioactive water. Attenuation correction was performed using µ-maps derived from CT data, while scatter and septal penetration corrections were performed using the transmission-dependent convolution-subtraction method. SPECT acquisitions were finally corrected for dead time and partial volume effects. Image analysis was performed using the commercial QSPECT software. The quantitative SPECT approach was validated on an anthropomorphic phantom provided with a home-made insert simulating a hepatic lesion. Quantitative accuracy was studied using three tumour-to-background activity concentration ratios (6:1, 9:1, 14:1). For all acquisitions, the recovered total activity was within 12% of the calibrated activity both in the background region and in the tumour. Using a 6:1 tumour-to-background ratio the recovered total activity was within 2% in the tumour and within 5% in the background. Partial volume effects, if not properly accounted for, can lead to significant activity underestimations in clinical conditions. In conclusion, accurate activity quantification of 177Lu can be obtained if activity measurements are performed with equipment traceable to primary standards, advanced correction algorithms are used and acquisitions are performed at the 208keV photopeak using medium-energy collimators.

Concentration of 123I-metaiodobenzylguanidine in left and right liver lobes. Findings indicate regional differences in function in the normal liver.

PURPOSE: Normal radioactivity in the liver is often shown to be higher in the left lobe than in the right lobe at clinical examination by single photon emission computed tomography (SPECT) with 123I-metaiodobenzylguanidine (123I-MIBG). Our objective was to determine whether this represents a pathological condition. MATERIAL AND METHODS: The distribution of 123I-MIBG in the liver was retrospectively studied in clinical patients who had normal CT examinations of the liver and spleen. In the SPECT sections of 27 123I-MIBG examinations, we determined the activity ratios between the left and right lobes. The control group comprised 33 examinations with (111)In-pentetreotide (OctreoScan) and 23 examinations with 99mTc-antigranulocyte antibody. RESULTS: The mean activity ratio between left and right lobes for 123I-MIBG was 1.24, and for (111)In-pentetreotide 0.87. These figures differed significantly both from each other and from 1.00. The mean ratio for 99mTc-antibody at the early examinations was 0.99, and at the late examinations 0.95. These figures differed significantly from the values for 123I-MIBG and (111)In-pentetreotide. CONCLUSION: The increased concentration of 123I-MIBG in the left lobe of the liver compared to the right lobe is a normal finding. The reason for this cannot be explained. The difference in the way in which the left and right lobes deal with the three radiopharmaceuticals is a new finding and indicates a regional difference in liver function that has not been reported previously.

Resting state rCBF mapping with single-photon emission tomography and positron emission tomography: magnitude and origin of differences.

Single-photon emission tomography (SPET), using technetium-99m hexamethylpropylene amine oxime, and positron emission tomography (PET), using oxygen-15 butanol were compared in six healthy male volunteers with regard to the mapping of resting state regional cerebral blood flow (rCBF). A computerized brain atlas was utilized for 3D regional analyses and comparison of 64 selected and normalized volumes of interest (VOIs). The normalized mean rCBF values in SPET, as compared to PET, were higher in most of the Brodmann areas in the frontal and parietal lobes (4.8% and 8.7% respectively). The average differences were small in the temporal (2. 3%) and occipital (1.1%) lobes. PET values were clearly higher in small VOIs like the thalamus (12.3%), hippocampus (12.3%) and basal ganglia (9.9%). A resolution phantom study showed that the in-plane SPET/PET system resolution was 11.0/7.5 mm. In conclusion, SPET and PET data demonstrated a fairly good agreement despite the superior spatial resolution of PET. The differences between SPET and PET rCBF are mainly due to physiological and physical factors, the data processing, normalization and co-registration methods. In order to further improve mapping of rCBF with SPET it is imperative not only to improve the spatial resolution but also to apply accurate correction techniques for scatter, attenuation and non-linear extraction.

Optimal design of planar-concave collimators for SPECT--an analytical approach.

In this paper we present an analytical tool for the design and optimization of planar-concave collimators for SPECT. We conclude that a single general planar-concave collimator that eliminates the non-isotropic blurring for all SPECT applications does not exist. On the other hand, it is possible to achieve pseudo-optimal collimators for different clinical applications by a careful choice of the design parameters. By classifying the clinical applications into two groups, for instance body and brain studies, the non-isotropic blurring for most SPECT situations may be dramatically reduced by means of planar-concave collimators. The results based on Monte Carlo simulations show that the shape of the point source response function of the reconstructed image obtained from the planar-concave collimator is more isotropic than that obtained from a conventional parallel-hole collimator. Specifically, the ratio of the FWHM of the reconstructed point response function in the radial and tangential direction is increased from 0.5 for the parallel-hole to 0.85 for the planar-concave collimator for sources 200 mm away from the centre of rotation.

Effect of food intake on liver and spleen volume: assessment with single photon emission computed tomography.

RATIONALE AND OBJECTIVES: The authors evaluated the influence of food intake on liver and spleen size. The rationale was that since a meal induces a marked increase in splanchnic blood flow, organ volume might also be affected. This could influence conclusions made at clinical examination. METHODS: Single photon emission computed tomography (SPECT) was performed in 20 healthy volunteers after administration of technetium-99m albumin colloid before and after ingestion of a standardized meal. A semiautomatic technique was used to determine liver and spleen size. RESULTS: There was a nonsignificant reduction in liver volume of 1.5% (P = .063) and a significant reduction in spleen volume of 3.2% (P = .00033) after food intake. CONCLUSION: Liver and spleen volume are marginally affected by food intake, and the changes are within the methodologic error of radiologic modalities.

Evaluation of optimally designed planar-concave collimators in single-photon emission tomography.

The imaging properties of optimally designed planar-concave (PC) collimators were evaluated by means of Monte Carlo simulations. The evaluation was done with respect to total system spatial resolution and the overall image noise distribution in single-photon emission tomography. The results showed that the non-isotropy with PC collimators, assessed by the ratio of the full-width at half-maximum in the radial and tangential directions, was reduced by about 60% as compared with a conventional parallel-hole collimator for sources located 200 mm away from the centre of rotation. Furthermore, the image noise distribution along the object radius became more uniform when the curved collimator was used. The maximum increase in noise due to use of the curved collimator was about 45% close to the edge of the phantom, where the hole length was about 3 times longer. We also showed with Monte Carlo simulations that the spatial resolution of the lateral cortex when using the curved collimator was significantly improved due to improved radial resolution.

Collimator design for improved spatial resolution in SPECT and planar scintigraphy.

UNLABELLED: This paper evaluates the design of a new planar-concave collimator with nonuniform response that better matches the body shape than conventional collimators. METHODS: The collimator properties are evaluated and assessed by means of both a stimulation program and an experimental test using a prototype planar-concave collimator. RESULTS: The results, for points located 150 mm from the axis of rotation, demonstrate that the ratio of radial and tangential spatial resolution in SPECT with the new collimator decreased by 40%, as compared to SPECT with a standard collimator. In planar scintigraphy, the spatial resolution improved correspondingly from 10.9 mm (FWHM) to 7.8 mm in lateral areas of the body. CONCLUSION: The new collimator reduces nonisotropic blurring in SPECT in addition to improving spatial resolution in both planar scintigraphy and in SPECT.

A 3-D method for delineation of activity distributions and assessment of functional organ volumes with SPECT.

The distribution volume of an organ may have a clinical impact in many cases and various methods have been designed to make volume assessments. In this paper, we describe a new method for delineation of the distribution outline and volume determination. The method is based on smoothing, differentiation, image relaxation and voxel counting of single photon emission computer tomography (SPECT) image sets with 3-D operators. A special routine corrects for the inherent thickness of the voxel-based outline. Phantom experiments, using a SPECT system with LEGP-collimator and a 64 x 64 acquisition matrix with 6.3 x 6.3 mm2 pixel size, demonstrated good correlation between the measured and the true volumes. For volumes larger than 120 cc the correlation coefficient was 0.9999 with SE 1.0 cc and an average relative deviation of 0.49%. For volumes below 120 cc, the accuracy was impaired due to low resolution power. By improving the system spatial resolution with an LEHR-collimator and a smaller pixel-size (4.1 x 4.1 mm2), good accuracy was achieved also for volumes in the range from 3 to 120 cc. Measurements of 15 differently shaped phantoms of volumes between 3 and 104 cc demonstrated high correlation between measured and true volumes: R = 0.9921 and SE = 0.74 cc (5.3%). For volumes as small as 3 and 5 cc, the difference between the true and the assessed volume was 0.6 cc. The reproducibility of the method was within 3% for volumes above 120 cc and within 7% for volumes below.(ABSTRACT TRUNCATED AT 250 WORDS)

Change in size, shape and radiocolloid uptake of the alcoholic liver during alcohol withdrawal, as demonstrated by single photon emission computed tomography.

The volume of the total liver and separate right and left lobes was studied before and after 1 week of alcohol withdrawal in 16 consecutive alcoholics by means of single photon emission computed tomography after intravenous injection of 99Tcm-human albumin colloid; the relative tissue distribution of radioactivity was also followed. The left liver lobe increased in volume more than the right lobe during drinking and decreased more rapidly after alcohol withdrawal. Median volume reductions during 1 week of alcohol withdrawal were: total liver 12%, left lobe 26%, and right lobe 8%, indicating that half of the reduction to values of a control group was achieved during this first week. The volume of the right but not of the left lobe was significantly correlated to body size in alcoholics and in controls. The left lobe had a lower capacity to concentrate the radiocolloid than the right lobe in alcoholics and in controls. The liver/spleen, liver/bone marrow and liver/background radioactivity concentration ratios in the alcoholics increased during alcohol withdrawal. We conclude that heavy drinking causes both an increased total liver volume and a change in liver shape, with a relatively more enlarged left than right lobe, as well as a decreased capacity to concentrate radiocolloid. These changes are rapidly reversible during abstinence from alcohol.

A better target-to-background activity ratio using a large-sized colloid compared to a nano-sized colloid for scintigraphy of the peripheral bone marrow. A study in mice and humans.

Small-sized radiocolloids with a diameter less than 100 nm (nanocolloids), reduce the confounding liver and spleen uptake compared to large-sized colloids at bone marrow scintigraphy. Consequently, nanocolloids are today generally used for this purpose. Such colloids, though, seem to produce considerable background activity, especially from the large vessels and the urinary tract. This has been studied in mice and humans using a nanocolloid and a large-sized colloid, both composed of human albumin. In mice, the findings confirm a lower relative and absolute uptake of the nanocolloid in the liver and spleen compared to the large-sized colloid, whereas the bone marrow activity relative to the activity of kidneys, heart, lungs, intestines and peripheral blood is higher for the large-sized colloid than for the nanocolloid. The latter was confirmed in humans who were examined by single photon emission computed tomography corrected for attenuation and scattering of photons. It is concluded that a large-sized colloid should be used for spot examination of a specific marrow region outside the liver and spleen, while a nanocolloid must be used when examining structures close to the liver and spleen as well as for depiction of the entire bone marrow.