Angel Torrado-Carvajal

Parallel transmit pulse design for patients with deep brain stimulation implants

Specific absorption rate (SAR) amplification around active implantable medical devices during diagnostic MRI procedures poses a potential risk for patient safety. In this study, we present a parallel transmit (pTx) strategy that can be used to safely scan patients with deep brain stimulation (DBS) implants.

Fast Patch-Based Pseudo-CT Synthesis from T1-Weighted MR Images for PET/MR Attenuation Correction in Brain Studies

Attenuation correction in hybrid PET/MR scanners is still a challenging task. This paper describes a methodology for synthesizing a pseudo-CT volume from a single T1-weighted volume, thus allowing us to create accurate attenuation correction maps. Methods: We propose a fast pseudo-CT volume generation from a patient-specific MR T1-weighted image using a groupwise patch-based approach and an MRI–CT atlas dictionary. For every voxel in the input MR image, we compute the similarity of the patch containing that voxel to the patches of all MR images in the database that lie in a certain anatomic neighborhood. The pseudo-CT volume is obtained as a local weighted linear combination of the CT values of the corresponding patches. The algorithm was implemented in a graphical processing unit (GPU). Results: We evaluated our method both qualitatively and quantitatively for PET/MR correction. The approach performed successfully in all cases considered. We compared the SUVs of the PET image obtained after attenuation correction using the patient-specific CT volume and using the corresponding computed pseudo-CT volume. The patient-specific correlation between SUV obtained with both methods was high (R2 = 0.9980, P < 0.0001), and the Bland–Altman test showed that the average of the differences was low (0.0006 ± 0.0594). A region-of-interest analysis was also performed. The correlation between SUVmean and SUVmax for every region was high (R2 = 0.9989, P < 0.0001, and R2 = 0.9904, P < 0.0001, respectively). Conclusion: The results indicate that our method can accurately approximate the patient-specific CT volume and serves as a potential solution for accurate attenuation correction in hybrid PET/MR systems. The quality of the corrected PET scan using our pseudo-CT volume is comparable to having acquired a patient-specific CT scan, thus improving the results obtained with the ultrashort-echo-time–based attenuation correction maps currently used in the scanner. The GPU implementation substantially decreases computational time, making the approach suitable for real applications.

SAR reduction in 7T C-spine imaging using a "dark modes" transmit array strategy.

Local specific absorption rate (SAR) limits many applications of parallel transmit (pTx) in ultra high‐field imaging. In this Note, we introduce the use of an array element, which is intentionally inefficient at generating spin excitation (a “dark mode”) to attempt a partial cancellation of the electric field from those elements that do generate excitation. We show that adding dipole elements oriented orthogonal to their conventional orientation to a linear array of conventional loop elements can lower the local SAR hotspot in a C‐spine array at 7 T.

Multi-atlas and label fusion approach for patient-specific MRI based skull estimation.

MRI‐based skull segmentation is a useful procedure for many imaging applications. This study describes a methodology for automatic segmentation of the complete skull from a single T1‐weighted volume.

An Embedded Systems Course for Engineering Students Using Open-Source Platforms in Wireless Scenarios

This paper presents a case study analyzing the advantages and disadvantages of using project-based learning (PBL) combined with collaborative learning (CL) and industry best practices, integrated with information communication technologies, open-source software, and open-source hardware tools, in a specialized microcontroller and embedded systems engineering Masters course. In addition to addressing industry requirements in both contents and methodology, the course develops capabilities and competencies in problem solving, independent learning, teamwork, and technical knowledge. Since PBL methodology alone does not ensure teamwork, it was complemented with CL. Design review meetings (as described in IEC 61160), deliverables, and organizational resources were also introduced to mirror industry demands. This structure integrated course content and student academic achievement in a simulated industrial environment. The course had students build a modular management system for home appliances, implementing control software on the “Arduino” open-source platform, as well as using wireless communications. The results show that teaching, learning, and student assessment processes can be improved by using PBL with CL. In addition, the introduction of industry practices, such us peer review meetings, brings academia closer to a real-world context.

Robust time-shifted spoke pulse design in the presence of large B0 variations with simultaneous reduction of through-plane dephasing, B1+ effects, and the specific absorption rate using parallel transmission

To design parallel transmission spokes pulses with time‐shifted profiles for joint mitigation of intensity variations due to B1+ effects, signal loss due to through‐plane dephasing, and the specific absorption rate (SAR) at 7T.

A Multi-Atlas and Label Fusion Approach for Patient-Specific MRI Based Skull Segmentation

MRI‐based skull segmentation is a useful procedure for many imaging applications. This study describes a methodology for automatic segmentation of the complete skull from a single T1‐weighted volume.

Radiofrequency heating studies on anesthetized swine using fractionated dipole antennas at 10.5 T

To validate electromagnetic and thermal simulations with in vivo temperature measurements, and to demonstrate a framework that can be used to predict temperature increase caused by radiofrequency (RF) excitation with dipole transmitter arrays.

The Effect of Mouth Motion on the Attenuation Correction in Neurological PET Studies

In each new generation of PET scanners, the axial field-of-view (FOV) has been increased as a way to improve their sensitivity and obtain better images, faster and with lower injected doses. Nevertheless, in neurological studies, the use of larger axial FOV can introduce errors in the PET attenuation correction (AC), as possible movements of the patient’s mouth are not currently considered. This effect happens when oblique PET sinograms containing both the jaw and the brain are used. In this work we have studied the bias that mouth motion can introduce in the PET AC, for two different scanners. The average effect over large regions in the brain is around 1 % for a moderate mouth motion, although some voxels show differences of up to 18 %. These results indicate that if scanners with large axial FOV and acceptance angles are going to be used in the future, possible movements of patient’s mouth should be considered in the AC procedure.

Dixon-VIBE Deep Learning (DIVIDE) Pseudo-CT Synthesis for Pelvis PET/MR Attenuation Correction

Whole-body attenuation correction (AC) is still challenging in combined PET/MR scanners. We describe Dixon-VIBE Deep Learning (DIVIDE), a deep-learning network that allows synthesizing pelvis pseudo-CT maps based only on the standard Dixon volumetric interpolated breath-hold examination (Dixon-VIBE) images currently acquired for AC in some commercial scanners. Methods: We propose a network that maps between the four 2-dimensional (2D) Dixon MR images (water, fat, in-phase, and out-of-phase) and their corresponding 2D CT image. In contrast to previous methods, we used transposed convolutions to learn the up-sampling parameters, we used whole 2D slices to provide context information, and we pretrained the network with brain images. Twenty-eight datasets obtained from 19 patients who underwent PET/CT and PET/MR examinations were used to evaluate the proposed method. We assessed the accuracy of the μ-maps and reconstructed PET images by performing voxel- and region-based analysis comparing the SUVs (in g/mL) obtained after AC using the Dixon-VIBE (PETDixon), DIVIDE (PETDIVIDE), and CT-based (PETCT) methods. Additionally, the bias in quantification was estimated in synthetic lesions defined in the prostate, rectum, pelvis, and spine. Results: Absolute mean relative change values relative to CT AC were lower than 2% on average for the DIVIDE method in every region of interest except for bone tissue, where it was lower than 4% and 6.75 times smaller than the relative change of the Dixon method. There was an excellent voxel-by-voxel correlation between PETCT and PETDIVIDE (R2 = 0.9998, P < 0.01). The Bland–Altman plot between PETCT and PETDIVIDE showed that the average of the differences and the variability were lower (mean PETCT–PETDIVIDE SUV, 0.0003; PETCT–PETDIVIDE SD, 0.0094; 95% confidence interval, [−0.0180,0.0188]) than the average of differences between PETCT and PETDixon (mean PETCT–PETDixon SUV, 0.0006; PETCT–PETDixon SD, 0.0264; 95% confidence interval, [−0.0510,0.0524]). Statistically significant changes in PET data quantification were observed between the 2 methods in the synthetic lesions, with the largest improvement in femur and spine lesions. Conclusion: The DIVIDE method can accurately synthesize a pelvis pseudo-CT scan from standard Dixon-VIBE images, allowing for accurate AC in combined PET/MR scanners. Additionally, our implementation allows rapid pseudo-CT synthesis, making it suitable for routine applications and even allowing retrospective processing of Dixon-VIBE data.