Abstract
ObjectivesVisualization 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.MethodsMR 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).ResultsThe 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.ConclusionsSynthetic 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.
Highlights
Introduction suchsynthetic computed tomography (CT) (sCT) images could be generated from MR images acquired during the treatment session to depict the bone distribution in the treatment position
Synthetic computed tomography images intrinsically aligned with treatment MR images may have the potential to facilitate
By qualitatively and quantitatively comparing synthetic CT (sCT) with CT, we investigated the potential of sCT images for visualizing cancellous and cortical bone in patients with bone metastases
Summary
SCT images could be generated from MR images acquired during the treatment session to depict the bone distribution in the treatment position. We implemented a fast and automated method for sCT generation that enables the combined visualization of soft tissue and cortical bone. By qualitatively and quantitatively comparing sCT with CT, we investigated the potential of sCT images for visualizing cancellous and cortical bone in patients with bone metastases. Magnetic resonance imaging–guided high-intensity focused ultrasound (MRI-HIFU) has shown promising results for therapy in bones and joints [1,2,3,4]. MRI-HIFU has shown potential for pain palliation in patients with bone metastases [5], where the suspected mechanism of action is the thermal ablation of the nerves that produce the pain [6,7,8]
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