Quantitation of Benzodiazepine Receptors in Human Brain Using the Partial Saturation Method

The in vivo quantification of the benzodiazepine receptor concen tration in humans using PET and flumazenil (FMZ) is usually based on Scatchard analysis when the goal is to avoid blood sampling. The experimental protocols, however, include several (at least two) experiments with various specific activities in the same subject to obtain a range of bound ligand concentrations. Methods: We propose the partial saturation method, which is based on a natural decrease in bound ligand concentration after an FMZ injection with an average dose between a tracer dose and a saturation dose. An adequate range of bound ligand concentrations can thus be ob tained from a single experiment. The free ligand concentration is estimated from the PET measurement in the pons after correction for the effect of the small receptor site concentration in this reference region. Results: The receptor concentration and affinity estimates obtained with this approach in six regions of interest agree with previously published values obtained by using more complex ap proaches. Receptor concentration appears to be insensitive to the uncertainties with regard to the receptor site concentration in the pons. Conclusion: The partial saturation protocol can be used to estimate both the benzodiazepine receptor concentration and the FMZ affinity in routine examinations in adults (or even in children) using a single 40-min experiment without blood sampling

Bromine-76-Metabromobenzylguanidine: A PET Radiotracer for Mapping Sympathetic Nerves of the Heart

Iodine-123-metaiodobenzylguanidine (MIBG) is used to qualitatively assess heart innervation with single-photon emission computed tomography (SPECT). This approach is clinically useful in the prognostic evaluation of congestive heart failure. To improve quantification of uptake of the tracer using positron emission tomography (PET), we studied the characteristics of the bromoanalog of MIBG. Bromine-76-metabromobenzylguanidine (76Br-MBBG) was prepared from a heteroisotopic exchange between radioactive bromine atoms (noncarrier-added (76Br) BrNH4) and the cold iodine atoms of the precursor metaiodobenzylguanidine. Biodistribution was studied in rats and PET cardiac imaging performed in dogs. Myocardial uptake was high and prolonged in both species (mean half-life in dogs: 580 min). In rats, myocardial uptake was inhibited by desipramine by 64%, whereas after pretreatment with 6- hydroxydopamine uptake was reduced by 84%. In dogs pretreated with 6- hydroxydopamine or with desipramine, a steep washout of the tracer occurred (mean half-life: 136 min and 118 min, respectively). The non-specific uptake plus the passive neuronal diffusion of the tracer could be estimated at about 25%-30% of the total fixation. In dogs, analysis of unchanged 76Br-MBBG in plasma showed that radiotracer metabolism was slow: 60 min after injection, 80% of the radioactivity was related to unchanged 76Br-MBBG. These preliminary findings suggest that 76Br-MBBG could be used to quantitatively assess adrenergic innervation in heart disease using PET. When combined with use of 11C-CGP 12177, cardiac adrenergic neurotransmission can be assessed

From a PMT-based to a SiPM-based PET system: a study to define matched acquisition/reconstruction parameters and NEMA performance of the Biograph Vision 450

International audienceBackground: The purpose of this work was to propose an approach based on noise measurement to adapt present clinical acquisition and reconstruction parameters adapted to a PMT-based system (Biograph mCT) to a SiPM-based system (Biograph Vision 450) sharing identical geometrical properties. The NEMA performance (NEMA) of the recently released Biograph Vision 450 PET/CT (Vision) was also derived.Methods: All measurements were conducted on Vision and Biograph mCT with TrueV (mCT). A full NEMA-based performance was derived for Vision only. The adaptation of acquisition and reconstruction parameters from mCT to Vision was done using the NEMA image quality phantom. The noise level reached using mCT was set as the reference value for six different numbers of net true coincidences. The noise level computed using Vision was matched to the reference noise level (within 0.01%) using a different reconstruction set-up to determine the potential reduction of count numbers for the same noise level.Results: Vision sensitivity was 9.1 kcps/MBq for a timing resolution of 213 ps at 5.3 kBq/mL. The NEMA-based CR for the 10-mm sphere was better than 75% regardless the reconstruction set-up studied. The mCT reference noise properties could be achieved using Vision with a scan time reduction (STR) of 1.34 with four iterations and a 440 × 440 matrix size (or STR = 1.89 with a 220 × 220 matrix size) together with a 3D CR improvement of 53% for the 10-mm sphere (24% using 220 × 220).Conclusion: The Vision exhibited improved NEMA performances compared to mCT. Using the proposed approach, the time acquisition could be divided by almost two, while keeping the same noise properties as that of mCT with a marked improvement of contrast recovery

CQZ;01DEC99

Abstract. Epidepride labelled with iodine-123 is a suitable probe for the in vivo imaging of striatal and extrastriatal dopamine D 2 receptors using single-photon emission tomography (SPET). Recently, this molecule has also been labelled with carbon-11. The goal of this work was to develop a method allowing the in vivo quantification of radioactivity uptake in baboon brain using SPET and to validate it using positron emission tomography (PET). SPET studies were performed in Papio anubis baboons using 123 I-epidepride. Emission and transmission measurements were acquired on a dual-headed system with variable head angulation and low-energy ultra-high resolution (LEUHR) collimation. The imaging protocol consisted of one transmission measurement (24 min, heads at 90°), obtained with two sliding line sources of gadolinium-153 prior to injection of 0.21-0.46 GBq of 123 I-epidepride, and 12 emission measurements starting 5 min post injection. For scatter correction (SC) we used a dual-window method adapted to 123 I. Collimator blurring correction (CBC) was done by deconvolution in Fourier space and attenuation correction (AT) was applied on a preliminary (CBC) filtered back-projection reconstruction using 12 iterations of a preconditioned, regularized minimal residual algorithm. For each reconstruction, a calibration factor was derived from a uniform cylinder filled with a 123 I solution of a known radioactivity concentration. Calibration and baboon images were systematically built with the same reconstruction parameters. Uncorrected (UNC) and (AT), (SC+AT) and (SC+CBC+AT) corrected images were compared. PET acquisitions using 0.11-0.44 GBq of 11 C-epidepride were performed on the same baboons and used as a reference. The radioactive concentrations expressed in percent of the injected dose per 100 ml (%ID/100 ml) obtained after (SC+CBC+AT) in SPET are in good agreement with those obtained with PET and 11 Cepidepride. A method for the in vivo absolute quantitation of 123 I-epidepride uptake using SPET has been developed which can be directly applied to other 123 I-labelled molecules used in the study of the dopamine system. Further work will consist in using PET to model the radioligandreceptor interactions and to derive a simplified model applicable in SPET

Fast non-supervised 3D registration of PET and MR images of the brain

Submitted to the 'Journal of cerebral blood flow and metabolism' in July 1993Available at INIST (FR), Document Supply Service, under shelf-number : RP 12055 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueSIGLEFRFranc