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Quantitative evaluation of internal marks made using MRgFUS as seen on MRI, CT, US, and digital color images - a
Elizabeth Hipp1, Xiaobing Fan1, Ari Partanen2
1Department of Radiology, University of Chicago, Chicago, IL 60637, USA.
Abstract:
This pilot study compared the detectability of internal thermal marks produced with MRI-guided focused ultrasound (MRgFUS) on MRI, computed tomography (CT), ultrasonography (US), and color images from digital scanning. Internal marks made using MRgFUS could potentially guide surgical, biopsy or radiotherapy procedures. New Zealand White rabbits (n = 6) thigh muscle were marked using a Philips MRgFUS system. Before and after sonications, rabbits were imaged using T1- and T2-weighted MRI. Then rabbits were sacrificed and imaging was performed using CT and US. After surgical excision specimens were scanned for color conspicuity analysis. Images were read by a radiologist and quantitative analysis of signal intensity was calculated for marks and normal muscle. Of a total of 19 excised marks, approximately 79%, 63%, and 62% were visible on MRI, CT, and US, respectively. The average maximum temperature elevation in the marks during MRgFUS was 39.7 ± 10.1 °C, and average dose diameter (i.e., the diameter of the area that achieved a thermal dose greater than 240 cumulative equivalent minutes at 43 °C) of the mark at the focal plane was 7.3 ± 2.1 mm. On MRI the average normalized signal intensities were significantly higher in marks compared to normal muscle (p < 0.05). On CT, the marked regions were approximately 10 HU lower than normal muscle (p < 0.05). The results demonstrate that MRgFUS can be used to create internal marks that are visible on MRI, CT and US.
Insights
Magnetic Resonance Imaging-guided Focused Ultrasound (MRgFUS) successfully created internal thermal marks in rabbit muscle. These MRgFUS-generated marks were detectable using Magnetic Resonance Imaging (MRI), computed tomography (CT), and ultrasonography (US).
Area of Science:
- Biomedical Engineering
- Medical Imaging
- Interventional Radiology
Background:
- Accurate internal targeting is crucial for minimally invasive procedures like surgery, biopsy, and radiotherapy.
- Current methods for creating surgical or biopsy guidance markers have limitations.
- Magnetic Resonance Imaging-guided Focused Ultrasound (MRgFUS) offers a non-invasive approach to thermal ablation and tissue manipulation.
Purpose of the Study:
- To evaluate the feasibility of using MRgFUS to create internal thermal marks.
- To compare the detectability of these MRgFUS-induced marks across multiple imaging modalities: MRI, CT, US, and digital color scanning.
- To assess the potential of MRgFUS marks as fiducials for image-guided interventions.
Main Methods:
- MRgFUS was employed to create thermal marks in the thigh muscle of New Zealand White rabbits.
- Post-sonication imaging included T1- and T2-weighted MRI, CT, and US.
- Excision specimens were analyzed for color conspicuity, and quantitative signal intensity analysis was performed for MRI and CT.
Main Results:
- MRgFUS successfully generated internal thermal marks.
- Detectability rates were approximately 79% for MRI, 63% for CT, and 62% for US.
- Significant differences in signal intensity (MRI) and Hounsfield units (CT) were observed between marks and normal muscle tissue, confirming visibility.
Conclusions:
- MRgFUS is a viable method for creating internal thermal marks within biological tissue.
- These MRgFUS-induced marks demonstrate good visibility across conventional radiological imaging techniques (MRI, CT, US).
- MRgFUS-generated marks hold promise as internal fiducials to guide future image-guided surgical, biopsy, and radiotherapy procedures.