Hot and cold contrasts in high resolution Tc-99m planar scintigraphy: a survey of fifty-two camera heads using the PICKER thyroid phantom

This study aimed at comparing the sensitivity and hot and cold contrasts obtained when imaging the Picker thyroid phantom using gamma cameras fitted with either their ultra-high or high-resolution low energy parallel hole collimator. Seventeen camera models from Elscint, General Electric, Siemens and Sopha Medical Vision were involved in the study for a total of 30 cameras and 52 camera heads. A single operator conducted the study in order to minimize the impact of human factors. The phantom contained about 74 MBq 99mTc and was imaged at 10-cm from the collimator face with the energy window recommended by the camera manufacturer. A total of 1 million counts were accumulated. Hot and cold contrasts were in mean about 0.05 higher when using an ultra-high-resolution than when using a high-resolution low energy collimator. This higher contrast was obtained at the expense of a mean reduction in sensitivity of 30%. In particular, Elscint cameras demonstrated a 30% lower sensitivity whatever the collimator type. The Sopha Medical Vision DST and DSX cameras and the General Electric Magicam camera offered the lowest contrasts among the cameras with a high-resolution collimator. Although this was accompanied by a higher than the mean sensitivity for the DST and DSX, the Magicam demonstrated sensitivity roughly identical to the mean of all the cameras with a high-resolution collimator.Peer reviewe

Exploring with [18F]UCB-H the in vivo cariations in SV2A expression through the kainic acid rat model of temporal lobe epilepsy

Purpose The main purpose of this study was to understand how the positron emission tomography (PET) measure of the synaptic vesicle 2A (SV2A) protein varies in vivo during the development of temporal lobe epilepsy (TLE) in the kainic acid rat model. Procedures Twenty Sprague Dawley male rats were administered with multiple systemic doses of saline (control group, n = 5) or kainic acid (5 mg/kg/injection, epileptic group, n = 15). Both groups were scanned at the four phases of TLE (early, latent, transition, and chronic phase) with the [F-18]UCB-H PET radiotracer and T2-structural magnetic resonance imaging. At the end of the scans (3 months post-status epilepticus), rats were monitored for 7 days with electroencephalography for the detection of spontaneous electrographic seizures. Finally, the immunofluorescence staining for SV2A expression was performed. Results Control rats presented a significant increase in [F-18]UCB-H binding at the last two scans, compared with the first ones (p < 0.001). This increase existed but was lower in epileptic animals, producing significant group differences in all the phases of the disease (p < 0.028). Furthermore, the quantification of the SV2A expression in vivo with the [F-18]UCB-H radiotracer or ex vivo with immunofluorescence led to equivalent results, with a positive correlation between both. Conclusions Even if further studies in humans are required, the ability to detect a progressive decrease in SV2A expression during the development of temporal lobe epilepsy supports the use of [F-18]UCB-H as a useful tool to differentiate, in vivo, between healthy and epileptic animals along with the development of the epileptic disease

Use of a beta microprobe system to measure arterial input function in PET via an arteriovenous shunt in rats

Kinetic modeling of physiological function using imaging techniques requires the accurate measurement of the time-activity curve of the tracer in plasma, known as the arterial input function (IF). The measurement of IF can be achieved through manual blood sampling, the use of small counting systems such as beta microprobes, or by derivation from PET images. Previous studies using beta microprobe systems to continuously measure IF have suffered from high background counts. In the present study, a light-insensitive beta microprobe with a temporal resolution of up to 1 s was used in combination with a pump-driven femoral arteriovenous shunt to measure IF in rats. The shunt apparatus was designed such that the placement of the beta microprobe was highly reproducible. The probe-derived IF was compared to that obtained from manual sampling at 5-s intervals and IF derived from a left ventricle VOI in a dynamic PET image of the heart. Probe-derived IFs were very well matched to that obtained by "gold standard" manual blood sampling, but with an increased temporal resolution of up to 1 s. The area under the curve (AUC) ratio between probe- and manually derived IFs was 1.07 ± 0.05 with a coefficient of variation of 0.04. However, image-derived IFs were significantly underestimated compared to the manually sampled IFs, with an AUC ratio of 0.76 ± 0.24 with a coefficient of variation of 0.32. IF derived from the beta microprobe accurately represented the IF as measured by blood sampling, was reproducible, and was more accurate than an image-derived technique. The use of the shunt removed problems of tissue-background activity, and the use of a light-tight probe with minimal gamma sensitivity refined the system. The probe/shunt apparatus can be used in both microprobe and PET studies

In vivo exploration of synaptic projections in frontotemporal dementia.

The purpose of this exploratory research is to provide data on synaptopathy in the behavioral variant of frontotemporal dementia (bvFTD). Twelve patients with probable bvFTD were compared to 12 control participants and 12 patients with Alzheimer’s disease (AD). Loss of synaptic projections was assessed with ­[18F]UCBH-PET. Total distribution volume was obtained with Logan method using carotid artery derived input function. Neuroimages were analyzed with SPM12. Verbal fluency, episodic memory and awareness of cognitive impairment were equally impaired in patients groups. Compared to controls, ­[18F]UCBH uptake tended to decrease in the right anterior parahippocampal gyrus of bvFTD patients. Loss of synaptic projections was observed in the right hippocampus of AD participants, but there was no significant difference in ­[18F]UCBH brain uptake between patients groups. Anosognosia for clinical disorder was correlated with synaptic density in the caudate nucleus and the anteromedial prefrontal cortex. This study suggests that synaptopathy in bvFTD targets the temporal social brain and self-referential processes

In vivo imaging of synaptic loss in Alzheimer’s disease with [18F]UCB-H Positron Emission Tomography

IUAP - Interuniversity Attraction Poles Programme (IUAP 7/11); ARC - Actions de recherche concertées (ARC 12/17-01); Special Research Funds classical grant 2016 (Faculty of Medicine, University of Liege, Belgium), FRS-FNR

Median root prior and ordered subsets in Bayesian image reconstruction of single-photon emission tomography

Median root prior allows Bayesian image reconstruction without any a priori knowledge of the final solution. It limits the noise generated by maximum likelihood-expectation maximization, including when the ordered subsets accelerating procedure is used. Therefore the number of iterations can be optimized to obtain the best resolution for cold lesions. Moreover, the higher the number of subsets, the better the contrast, with optimal results for subsets containing between four and eight projections

Comparison of denoising techniques of scintigraphic images

peer reviewedScintigraphic images are strongly affected by Poisson noise. This article presents the results of a comparison between denoising methods for Poisson noise according to different criteria: the gain in signal-to-noise ratio, the preservation of resolution and contrast, and the visual quality. The wavelet techniques recently developed to denoise Poisson noise limited images are divided into two groups based on: (1) the Haar representation, (2) the transformation of Poisson noise into white Gaussian noise by the Haar–Fisz transform followed by a denoising. In this study, three variants of the first group and three variants of the second, including the adaptative Wiener filter, four types of wavelet thresholdings and the Bayesian method of Pizurica were compared to Metz and Hanning filters and to Shine, a systematic noise elimination process. All these methods, except Shine, are parametric. For each of them, ranges of optimal values for the parameters were highlighted as a function of the aforementioned criteria. The intersection of ranges for the wavelet methods without thresholding was empty, and these methods were therefore not further compared quantitatively. The thresholding techniques and Shine gave the best results in resolution and contrast. The largest improvement in signal-to-noise ratio was obtained by the filters. Ideally, these filters should be accurately defined for each image. This is difficult in the clinical context. Moreover, they generate oscillation artefacts. In addition, the wavelet techniques did not bring significant improvements, and are rather slow. Therefore, Shine, which is fast and works automatically, appears to be an interesting alternative.Les images scintigraphiques sont fortement affectées par du bruit poissonnien. Cet article présente les résultats d’une comparaison de débruiteurs de bruit poissonnien selon différents critères : le gain en rapport signal-sur-bruit, la préservation de la résolution et du contraste, et la qualité visuelle. Les techniques en ondelettes récentes pour débruiter un bruit poissonnien se répartissent en deux classes, basées sur : (1) la représentation de Haar, (2) la transformation du bruit poissonnien en bruit gaussien blanc par la transformée de Haar–Fisz suivie d’un débruitage. Trois variantes de la première classe et trois de la deuxième intégrant le filtre adaptatif de Wiener, quatre types de seuillage en ondelettes et la méthode bayesienne de Pizurica ont été comparées aux filtres de Metz et de Hanning et à Shine, un procédé systématique d’élimination de bruit. Toutes ces méthodes, excepté Shine, sont paramétriques. Pour chacune d’elles, des domaines de valeurs optimales des paramètres ont été mis en évidence en fonction des critères précités. Comme l’intersection de ces domaines était vide pour les méthodes en ondelettes sans seuillage, elles n’ont pas été comparées quantitativement. Les techniques de seuillage et Shine ont donné les meilleurs résultats en terme de résolution et de contraste. La meilleure amélioration en rapport signal-sur-bruit a été obtenue par les filtres. Idéalement, ceux-ci doivent être précisément définis pour chaque image, ce qui est difficile dans le contexte clinique. En outre, ils génèrent des artefacts sous forme d’oscillations. Par ailleurs, les techniques en ondelettes, assez lentes, n’ont pas apporté d’améliorations significatives. Ainsi, Shine, rapide et automatique, apparaît être une alternative intéressante

Quantitative capabilities of four state-of-the-art SPECT-CT cameras

Background. Four state-of-the-art single-photon emission computed tomography-computed tomography (SPECT-CT) systems, namely Philips Brightview, General Electric Discovery NM/CT 670 and Infinia Hawkeye 4, and Siemens Symbia T6, were investigated in terms of accuracy of attenuation and scatter correction, contrast recovery for small hot and cold structures, and quantitative capabilities when using their dedicated three-dimensional iterative reconstruction with attenuation and scatter corrections and resolution recovery. Methods. The National Electrical Manufacturers Association (NEMA) NU-2 1994 phantom with cold air, water, and Teflon inserts, and a homemade contrast phantom with hot and cold rods were filled with 99mTc and scanned. The acquisition parameters were chosen to provide adequate linear and angular sampling and high count statistics. The data were reconstructed using Philips Astonish, General Electric Evolution for Bone, or Siemens Flash3D, eight subsets, and a varying number of iterations. A procedure similar to the one used in positron emission tomography (PET) allowed us to obtain the factor to convert counts per pixel into activity per unit volume. Results. Edge and oscillation artifacts were observed with all phantoms and all systems. At 30 iterations, the residual fraction in the inserts of the NEMA phantom fell below 3.5%. Contrast recovery increased with the number of iterations but became almost saturated at 24 iterations onwards. In the uniform part of the NEMA and contrast phantoms, a quantification error below 10% was achieved. Conclusions. In objects whose dimensions exceeded the SPECT spatial resolution by several times, quantification seemed to be feasible within 10% error limits. A partial volume effect correction strategy remains necessary for the smallest structures. The reconstruction artifacts nevertheless remain a handicap on the road towards accurate quantification in SPECT and should be the focus of further works in reconstruction tomography