Synthetic CT for the planning of MR-HIFU treatment of bone metastases in pelvic and femoral bones: a feasibility study

Abstract

Objectives Visualization of the bone distribution is an important prerequisite for MRI-guided high-intensity focused ultrasound (MRI-HIFU) treatment planning of bone metastases. In this context, we evaluated MRI-based synthetic CT (sCT) imaging for the visualization of cortical bone. Methods MR and CT images of nine patients with pelvic and femoral metastases were retrospectively analyzed in this study. The metastatic lesions were osteolytic, osteoblastic or mixed. sCT were generated from pre-treatment or treatment MR images using a UNet-like neural network. sCT was qualitatively and quantitatively compared to CT in the bone (pelvis or femur) containing the metastasis and in a region of interest placed on the metastasis itself, through mean absolute difference (MAD), mean difference (MD), Dice similarity coefficient (DSC), and root mean square surface distance (RMSD). Results The dataset consisted of 3 osteolytic, 4 osteoblastic and 2 mixed metastases. For most patients, the general morphology of the bone was well represented in the sCT images and osteolytic, osteoblastic and mixed lesions could be discriminated. Despite an average timespan between MR and CT acquisitions of 61 days, in bone, the average (± standard deviation) MAD was 116 ± 26 HU, MD − 14 ± 66 HU, DSC 0.85 ± 0.05, and RMSD 2.05 ± 0.48 mm and, in the lesion, MAD was 132 ± 62 HU, MD − 31 ± 106 HU, DSC 0.75 ± 0.2, and RMSD 2.73 ± 2.28 mm. Conclusions Synthetic CT images adequately depicted the cancellous and cortical bone distribution in the different lesion types, which shows its potential for MRI-HIFU treatment planning. Key Points • Synthetic computed tomography was able to depict bone distribution in metastatic lesions. • Synthetic computed tomography images intrinsically aligned with treatment MR images may have the potential to facilitate MR-HIFU treatment planning of bone metastases, by combining visualization of soft tissues and cancellous and cortical bone.

MRI-based synthetic CT: a new method for structural damage assessment in the spine in patients with axial spondyloarthritis – a comparison with low-dose CT and radiography

“…While not previously tested in the spine in patients with axSpA, the MRI-based sCT method has been clinically validated in the cervical spine,30 the lumbar spine for surgical planning,31 and in the hip and SIJs 22 31–35. Morbée et al have reported equivalency of sCT to conventional CT regarding geometrical measurements when quantitively assessing bony morphology of the lumbar spine 31.…”

Anatomical variation of the sacroiliac joints: an MRI study with synthetic CT images

“…All anatomical characteristics were determined based on the sCT images, and dynamic multiplanar reconstruction (available as a tool in PACS) was allowed. No paired CT data were used as this imaging technique has been clinically validated by several previous studies [13][14][15][16][17][18][19].…”

“…Moreover, these sCT images allow for postprocessing with multiplanar reconstruction, which is practical and useful when examining the complex anatomical structure of the SIJ. This technique has been clinically validated in the SIJ, hips, lumbar spine and cervical spine [13][14][15][16][17][18][19]. In a recent study by Jans et al [14], sCT outperformed T1-weighted MRI images for detection of erosions, sclerosis, and ankylosis of the SIJ in patients with axial spondyloarthritis (axSpA), with reliability comparable to that of CT.…”

“…In a recent study by Jans et al [14], sCT outperformed T1-weighted MRI images for detection of erosions, sclerosis, and ankylosis of the SIJ in patients with axial spondyloarthritis (axSpA), with reliability comparable to that of CT. In addition to the SIJ, the reliability of sCT in comparison with conventional CT has been demonstrated for the pelvis including hips [15,17,18], lumbar spine [16], and cervical spine [19]. We aimed to evaluate the prevalence of SIJ variants on sCT images in a group of patients clinically suspected of axial axSpA, and to analyze the relationship between SIJ variants and age, sex and body weight.…”

Synthetic CT in Musculoskeletal Disorders

“…Fewer studies applied deep learning methods of synthetic CT generation specifically to musculoskeletal disorders. Nevertheless, some studies showed high agreement between synthetic images generated by deep learning and CT, including in the evaluation of morphologic parameters of the hip, 119 surgical planning of the lumbar spine, 120,121 creation of 3D printed models for surgical planning, 122 detection of structural lesions in the sacroiliac joints, 123 and in the treatment planning of bone metastasis by MRI-guided high-intensity focused ultrasound 124 …”