Evaluation of a direct motion estimation/correction method in respiratory-gated PET/MRI with motion-adjusted attenuation

Abstract

Purpose: Respiratory motion compensation in PET/CT and PET/MRI is essential as motion is a source of image degradation (motion blur, attenuation artifacts). In previous work, we developed a direct method for joint image reconstruction/motion estimation (JRM) for attenuation-corrected (AC) respiratory-gated PET, which uses a single attenuation-map (l-map). This approach was successfully implemented for respiratory-gated PET/CT, but since it relied on an accurate l-map for motion estimation, the question of its applicability in PET/MRI is open. The purpose of this work is to investigate the feasibility of JRM in PET/MRI and to assess the robustness of the motion estimation when a degraded l-map is used. Methods: We performed a series of JRM reconstructions from simulated PET data using a range of simulated Dixon MRI sequence derived l-maps with wrong attenuation values in the lungs, from À100% (no attenuation) to +100% (double attenuation), as well as truncated arms. We compared the estimated motions with the one obtained from JRM in ideal conditions (no noise, true l-map as an input). We also applied JRM on 4 patient datasets of the chest, 3 of them containing hot lesions. Patient list-mode data were gated using a principal component analysis method. We compared SUV max values of the JRM reconstructed activity images and non motion-corrected images. We also assessed the estimated motion fields by comparing the deformed JRM-reconstructed activity with individually non-AC reconstructed gates. Results: Experiments on simulated data showed that JRM-motion estimation is robust to l-map degradation in the sense that it produces motion fields similar to the ones obtained when using the true l-map, regardless of the attenuation errors in the lungs (< 0.5% mean absolute difference with the reference motion field). When using a l-map with truncated arms, JRM estimates a motion field that stretches the l-map in order to match the projection data. Results on patient datasets showed that using JRM improves the SUV max values of hot lesions significantly and suppresses motion blur. When the estimated motion fields are applied to the reconstructed activity, the deformed images are geometrically similar to the non-AC individually reconstructed gates. Conclusion: Motion estimation by JRM is robust to variation of the attenuation values in the lungs. JRM successfully compensates for motion when applied to PET/MRI clinical datasets. It provides a potential alternative to existing methods where the motion fields are pre-estimated from separate MRI measurements.

Non-Rigid Event-by-Event Continuous Respiratory Motion Compensated List-Mode Reconstruction for PET

“…Nonetheless, no obvious artifacts were observed in the reconstruction results. Further investigation should be conducted on estimating the motion fields based on non-attenuation corrected PET images in non-rigid registration and compare to ground truth motion fields or by using a joint reconstruction and motion estimation approach [43,44].…”

The effect of magnetic field strength on the positron range and projected annihilation artifact in integrated PET/MR systems: A GATE Monte Carlo study

“…In addition, magnetic resonance (MR) imaging is a selective test for most neurological indications. [1][2][3][4][5][6][7][8][9] Moreover, no ionizing radiation in MRI is another important advantage compared with CT and it is important in children, young adults, and those who need frequent imaging during follow-up in a long period. Furthermore, the information extracted from multiparametric MRI (functional, spectroscopic, and diffusion weighted-imaging) is valuable and precise besides the molecular imaging of PET.…”

“…Better soft‐tissue contrast compared to computed tomography (CT) makes MRI a useful diagnostic tool that offers many advantages over PET/CT in the diagnosis or lesion characterization in tissues, such as the brain, head, neck, prostate, cervix, and breast, besides cardiovascular imaging. In addition, magnetic resonance (MR) imaging is a selective test for most neurological indications 1–9 . Moreover, no ionizing radiation in MRI is another important advantage compared with CT and it is important in children, young adults, and those who need frequent imaging during follow‐up in a long period.…”

Improved PET/CT Respiratory Motion Compensation by Incorporating Changes in Lung Density

“…Instead of deformation fields determined from image registration, the deformation can also be estimated directly from the acquired PET data. Joint reconstruction and motion estimation (JRM) [5]- [9] is a reconstruction strategy in which, from the entire PET acquisition (as well as a gated respiratory surrogate signal and a single CT image), it is possible to estimate an activity image and the deformation between (respiratory) states. The input single CT image does not need to correspond to one of the gates of the respiratory signal; the computed activity image corresponds to the same respiratory state as the attenuation map (obtained from the CT image).…”