Simultaneous Correction of Attenuation and Distance-dependent Resolution in Spect - An Analytical Approach

An approximate analytical solution of the problem of attenuation and distance-dependent resolution effects in single photon emission tomography is presented for the case of a uniform absorbing medium. The algorithm obtained is a generalization of the Bellini and co-workers formula correcting for the single attenuation effect and is derived by means of Fourier transforms only. The method has been validated on mathematical phantoms as well as on physical data

Improved solution for ill-posed linear systems using a constrained optimization ruled by a penalty: evaluation in nuclear medicine tomography

Ill-posed linear systems occur in many different fields. A class of regularization methods, called constrained optimization, aims to determine the extremum of a penalty function whilst constraining an objective function to a likely value. We propose here a novel heuristic way to screen the local extrema satisfying the discrepancy principle. A modified version of the Landweber algorithm is used for the iteration process. After finding a local extremum, a bound is performed to the 'farthest' estimate in the data space still satisfying the discrepancy principle. Afterwards, the modified Landweber algorithm is again applied to find a new local extremum. This bound-iteration process is repeated until a satisfying solution is reached. For evaluation in nuclear medicine tomography, a novel penalty function that preserves the edge steps in the reconstructed solution was evaluated on Monte Carlo simulations and using real SPECT acquisitions as well. Surprisingly, the first bound always provided a significantly better solution in a wide range of statistics

A non-negative fast multiplicative algorithm in 3D scatter-compensated SPET reconstruction.

Single-photon emission tomographic (SPET) reconstruction can be improved, especially for noisy images, by using the iterative expectation-maximization of the maximum-likelihood (EM-ML) algorithm. Its application to clinical routine is, however, hampered by the high number of iterations necessary to achieve acceptable results. Therefore various methods have been developed to accelerate the EM-ML algorithm. In this paper a new accelerated EM-ML-like multiplicative algorithm is proposed for SPET reconstruction. Contrary to some other accelerating methods, it preserves two of the most important properties of the EM-ML, namely pixel positivity inside the patient body and null activity outside. The convergence speed is improved by a factor which can reach 100 in high spatial frequency or low count regions. Good estimates in the low count region are obtained without any smoothing, even at typical routine clinical count rates. The algorithm used in conjunction with the 3D effective one scatter path model provides high-quality SPET images and accurate quantitation

Quantitation in SPECT using an effective model of the scattering

A new method for correcting simultaneously the attenuation, scatter and resolution effects in SPECT has been developed for the case of a homogeneous medium. It is based on an effective model of the scatter process. This model depends on only four parameters which are determined experimentally and remain independent of the geometry and of the dimensions of the scatter medium. The method uses the data from the peak events and does not need additional energy windows on the scattered events. An original filter is proposed to remove the noise due to the poor statistics of clinical data. Tests on phantoms varying in size and activity show that the model allows absolute activity determination with an accuracy of a few per cent

Evaluation of novel whole-body high-resolution rodent SPECT (Linoview) based on direct acquisition of linogram projections.

Studies of the biodistribution of radiolabeled compounds in rodents frequently are performed during the process of development of new pharmaceutical drugs. This article presents the evaluation of a new whole-body animal SPECT system, called the Linoview SPECT system. METHODS: Linoview SPECT is based on the linear orbit acquisition technique associated with slit-aperture collimators mounted on 4 pixelated CsI(Na) detectors composed of an array of small, individual crystal elements. Sliding iridium rods allow variation of the collimator aperture. Hot-rod and cold-rod phantoms filled with (99m)Tc were imaged. Mice were imaged, and kidney radioactivity was measured after injection of (99m)Tc-dimercaptosuccinic acid and (111)In-diethylenetriaminepentaacetic acid-d-Phe(1)-octreotide ((111)In-pentetreotide; Octreo-Scan(111)). RESULTS: Phantom studies showed that hot rods separated by 0.35 mm can be distinguished and that 0.65-mm-diameter cold rods can be visualized, both at low-counting-rate acquisitions (111 and 59 MBq x h, respectively). In both mouse studies, the SPECT images allowed a clear delineation of the radioactivity concentrated over the cortex area of the kidneys, whereas the pelvis and the pelviureteral junction (1 mm) appeared as cold areas. The quantitative data derived from SPECT were in good agreement with the radioactivity counting obtained with a gamma-counter after isolation of the kidneys. In addition, in the mouse injected with (111)In-pentetreotide, the kidney radioactivity distribution seen with SPECT was in agreement with the ex vivo autoradiograms of the isolated kidneys. CONCLUSION: The phantom studies showed a clear improvement of the spatial resolution over the results reported in the literature with other dedicated small-animal SPECT systems, especially in cold-rod phantom studies. The increased performance can be ascribed to the high stability of the system with regard to the statistical noise present in the acquired data. The mouse studies showed that this system will be most useful for in vivo high-resolution SPECT and quantitative biodistribution studies in rodents, even with medium-energy radioisotopes that are difficult to image, such as (111)In

Tumour control probability derived from dose distribution in homogeneous and heterogeneous models: Assuming similar pharmacokinetics, 125Sn 177Lu is superior to 90Y 177Lu in peptide receptor radiotherapy

Clinical trials on 177Lu 90Y therapy used empirical activity ratios. Radionuclides (RN) with larger beta maximal range could favourably replace 90Y. Our aim is to provide RN dose-deposition kernels and to compare the tumour control probability (TCP) of RN combinations. Dose kernels were derived by integration of the mono-energetic beta-ray dose distributions (computed using Monte Carlo) weighted by their respective beta spectrum. Nine homogeneous spherical tumours (125mm in diameter) and four spherical tumours including a lattice of cold, but alive, spheres (1, 3, 5, 7mm in diameter) were modelled. The TCP for 93Y, 90Y and 125Sn in combination with 177Lu in variable proportions (that kept constant the renal cortex biological effective dose) were derived by 3D dose kernel convolution. For a mean tumour-absorbed dose of 180 Gy, 2mm homogeneous tumours and tumours including 3mm diameter cold alive spheres were both well controlled (TCP > 0.9) using a 7525% combination of 177Lu and 90Y activity. However, 125Sn 177Lu achieved a significantly better result by controlling 1mm-homogeneous tumour simultaneously with tumours including 5mm diameter cold alive spheres. Clinical trials using RN combinations should use RN proportions tuned to the patient dosimetry. 125Sn production and its coupling to somatostatin analogue appear feasible. Assuming similar pharmacokinetics 125Sn is the best RN for combination with 177Lu in peptide receptor radiotherapy justifying pharmacokinetics studies in rodent of 125Sn-labelled somatostatin analogues. © 2012 Institute of Physics and Engineering in Medicine

90Y TOF-PET based EUD reunifies patient survival prediction in resin and glass microspheres radioembolization of HCC tumours

Clinical studies reported a twofold ratio between the efficacies per Gy of resin versus glass spheres. Our aim is to investigate whether this difference could result from the different degrees of heterogeneity in sphere distribution between the two medical devices. The 90Y TOF-PET based equivalent uniform doses (EUD) was used for this purpose. 58 consecutive HCC radioembolizations were retrospectively analyzed. Absorbed doses D and Jones–Hoban EUD in lesions were computed. Radioembolization efficacy was assessed using Kaplan–Meier survival curves. In order to match together the glass and resin spheres survival curves using a 40 Gy-threshold, an efficacy factor of 0.73 and 0.36 has to be applied on their absorbed dose, respectively. Using EUD, a nice matching between glass and resin survival curves was obtained with a better separation of the responding and not responding survival curves. The results clearly support the fact that the activity heterogeneity observed in 90Y TOF-PET post radioembolization does not only result from statistical noise, but also reflects the actual heterogeneity of the spheres distribution. Use of EUD reunifies the efficacy of the two medical devices

The low hepatic toxicity per gray of 90Y glass microspheres is linked to their transport in the arterial tree favoring a nonuniform trapping as observed in posttherapy PET imaging

90Y resin and glass microsphere liver radioembolizations delivering lobar doses of 70 and 120 Gy, respectively, display hepatic toxicity similar to 40-Gy fractionated external-beam radiotherapy. We investigated how the lower number of glass microspheres could induce a sufficiently nonuniform dose distribution explaining this paradox. Methods: Microscale dosimetry was assessed in the realistic liver model developed by Gulec et al. but using the Russell's dose deposition kernel. A lattice of hexagonal prisms represented the hepatic lobules. Two hepatic arterial tree models-that is, a fixed-length and a variable-branches length-were used for the microsphere transport. Equal or asymmetric microsphere relative-spreading probability between 2 daughter vessels was assumed. Several 120-Gy liver simulations were performed: periodic simulations, where 1 or 6 glass microspheres were trapped in all and in only 1 of 6 portal tracts, respectively, and random simulations, where glass microsphere trapping assumed an equal probability for all the portal tracts or a variable probability depending on the successions of artery connections leading to the portal tract, both for the 2 arterial tree models. Results: For the 2 uniform simulations, all hepatic structures received at least 100 Gy. The fast decrease of the 90Y kernel as the inverse of the square of the distance r is counterbalanced by the number of contributing lobules containing microspheres that increases as r2. The random simulation with equal-spreading probability gave for the less irradiated tissue a lobule dose distribution centered around 103 Gy (full width at half maximum, 20 Gy). The distribution became significantly asymmetric with the 60%-40% relative-spreading probability, with a shift of the maximum from 103 down to 50 Gy, and about 17% of the lobules got a dose lower than 40 Gy to their different structures. Conclusion: The large nonuniform trapping produced by the microsphere transport in the arterial tree jointly with the low number of injected glass microspheres begins to explain their lower hepatic toxicity per Gray. In addition, the nonuniform trapping supports the fact that the granular aspect of 90Y PET imaging observed in patients could represent some reality and not only statistical noise. Copyright © 2014 by the Society of Nuclear Medicine and Molecular Imaging, Inc

Intragastric distribution of a standardized meal in health and functional dyspepsia: correlation with specific symptoms.

In functional dyspepsia, abnormal intragastric distribution of a test meal has been identified but has never been correlated to any symptom pattern. The aim of this study was to compare the intragastric distribution of a meal between functional dyspepsia patients and controls, and to correlate distribution with symptom patterns, using scintigraphic gastric emptying studies. In forty patients with functional dyspepsia and 29 healthy volunteers, scintigraphic planar images were obtained immediately after ingestion of a mixed radiolabelled test meal and every 20 min for 2 h. The images of the stomach were divided into proximal and distal compartments. The mean intragastric distribution was similar in patients and controls. Over the whole test, 18 (45%) and 20 (50%) patients had a distal redistribution of the solid and liquid phase of the meal, respectively, while proximal retention of these phases was found in 13 (33%) and 9 (23%) patients. Early satiety was associated with early distal redistribution of the liquid phase and fullness was associated with late proximal retention. This study shows similar intragastric distribution of a test meal in health and functional dyspepsia. Within the patient group, an association between abnormal intragastric distribution patterns and symptom profiles was found, which might be related to different pathophysiological mechanisms

Hepatobiliary scintigraphy in a patient with bilhemia

A 4-year-old child referred for acute jaundice following percutaneous needle biopsy of the liver underwent hepatobiliary scintigraphy. Although all conventional liver tests suggested preservation of hepatocyte function, the tracer uptake in the liver appeared dramatically reduced at scintigraphy and the blood pool activity did not decrease significantly until the end of the study. Visualization of the bile ducts indicated, however, that the tracer was taken up by the hepatocyte and further excreted into the biliary tree. There was no tracer pooling in the biliary tree although no bowel activity was observed, even on delayed images. The association of persistent blood pool activity, bile duct visualization without tracer pooling, and nonvisualization of the bowel was caused by a continuous recirculation of the tracer from the biliary tree into the bloodstream. The presence of a biliovenous fistula was further proven by percutaneous transhepatic cholangiography performed 24 h later. Since 1975, only 16 cases of bilhemia have been reported. To the best of our knowledge the scintigraphic pattern of this rare but life-threatening complication has not previously been reported