Impact of Image-Space Resolution Modeling for Studies with the High-Resolution Research Tomograph

Abstract

Brain PET in small structures is challenged by low resolution inducing bias in the activity measurements. Improved spatial resolution may be obtained by using dedicated tomographs and more comprehensive modeling of the acquisition system during reconstruction. In this study, we assess the impact of resolution modeling (RM) during reconstruction on image quality and on the estimates of biologic parameters in a clinical study performed on a high-resolution research tomograph. Methods: An accelerated list-mode ordinary Poisson ordered-subset expectation maximization (OP-OSEM) algorithm, including sinogram-based corrections and an experimental stationary model of resolution, has been designed. Experimental phantom studies are used to assess contrast and noise characteristics of the reconstructed images. The binding potential of a selective tracer of the dopamine transporter is also assessed in anatomic volumes of interest in a 5-patient study. Results: In the phantom experiment, a slower convergence and a higher contrast recovery are observed for RM-OP-OSEM than for OP-OSEM for the same level of statistical noise. RM-OP-OSEM yields contrast recovery levels that could not be reached without RM as well as better visual recovery of the smallest spheres and better delineation of the structures in the reconstructed images. Statistical noise has lower variance at the voxel level with RM than without at matched resolution. In a uniform activity region, RM induces higher positive and lower negative correlations with neighboring voxels, leading to lower spatial variance. Clinical images reconstructed with RM demonstrate better delineation of cortical and subcortical structures in both time-averaged and parametric images. The binding potential in the striatum is also increased, a result similar to the one observed in the phantom study. Conclusion: In high-resolution PET, RM during reconstruction improves quantitative accuracy by reducing the partial-volume effects.

Single scan parameterization of space-variant point spread functions in image space via a printed array: the impact for two PET/CT scanners

“…For the model fitting we chose to parameterize the data as a weighted sum of 3-dimensional Gaussian distributions as opposed to using one Gaussian distribution combined from 2 half Gaussian functions (Panin et al 2006, Rapisarda et al 2010. This allowed us to model the long tails observed on the PSF unted for when only one Gaussian is used (Sureau et al 2008, Cloquet et al 2010. Other models could also be considered like the asymmetric modified Pearson model (Cloquet et al 2010).…”

In vivo Validation of Reconstruction-Based Resolution Recovery for Human Brain Studies

“…Nevertheless, improved resolution could be seen in the parametric V T images (Figure 3). Much higher differences between OP-OSEM and PVC-OP-OSEM were found in studies performed by Sureau et al (2008) and Varrone et al (2009). Both studies used dopamine transporter radioligands, which show a high contrast between the striatum and the surrounding tissue.…”

Towards Biological Target Volumes Definition for Radiotherapy Treatment Planning: Quo Vadis PET/CT?

“…Whilst the CT and MRI provide an overall spatial uncertainty of the order of 2 mm, the spatial resolution of the current commercially available PET/CT systems is more than double [90]. However, extensive research and development is currently under way aiming to improve the spatial resolution of PET images concentrating on different aspects of the image acquisition and reconstruction: partial volume effect, [91] depth of interaction, [92] scanner bed wobbling, [93] resolution modeling, [94] etc. Some time ago Siemens announced the introduction of a new HI-REZ PET/CT system that uses measured point spread function (PSF) matrix throughout the field of view (FOV) of the PET scanner to de-convolve the PET slice onto a 2 mm spatial resolution image.…”

“…In lung cancer patients, as well as other cancer sites severely affected by the respiratory motion (liver, esophagus, etc), 4D PET/CT should be sought of as the prerogative for an accurate both anatomical and functional pin-pointing tool [55][56][57]96,97]. In conjunction with beam delivery systems equipped with Real-time Position Management (RPM) option, 4D PET/CT might open a door for dose escalation protocols [92][93][94][95][96][97]. …”