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A Preliminary Study of the Geometric Distortion in Diffusion-Weighted Imaging of Magnetic Resonance Imaging Simulation

x liu, J Qiu, Peking Union Medical College HospitalBeijingCN

Presentations

(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose:
In order to reduce the geometric distortion of DWI, an improved method of DWI scanning technology in MRI simulation of radiotherapy was proposed.
Methods:
1. Using ACR phantom to conduct DWI scan of conventional head parameters, abdominal parameters and pelvic parameters, respectively, to measure the geometric distortion of the image and record the measurement results; 2. Carry out conventional DWI scan of 10 patients with rectal cancer pelvic scan, carry out GTV sketch of this group of images, and compare with GTV sketch of T2WI image of this patient, record the measurement results; 3. Apply resolve HD diffusion Scan sequence repeat the above tests, and record the measurement results; 4. Compare the operation complexity, ADC value change and work efficiency.
Results:
1. The measurement results of ACR phantom show that the geometric distortion of DWI is less than ± 1mm in the effective range of MRI scanning, and there is no significant difference between the T1 and T2 sequences detected by conventional methods; 2. The results of the comparison between the T1 and T2 images of 10 patients with rectal cancer using conventional DWI scanning sequence and the T1 and T2 images show that there is obvious distortion; 3. The resolution HD diffusion scanning sequence is used Compared with T1 and T2 images, 10 cases of rectal cancer showed lower geometric distortion. 4. There was no change in operation complexity, ADC value and work efficiency when scanning parameters were changed.
Conclusion: MRI is used to simulate the location of radiotherapy, its image should have high location accuracy and spatial structure accuracy, so geometric distortion has become one of the important indicators of clinical radiotherapy. Diffusion weighted imaging (DWI) scanning technology is different from the traditional MRI technology. It can carry out special imaging scanning through the diffusion movement of water molecules, providing tissue contrast different from the conventional MRI image, and providing clearer and accurate guidance for the clinician's radiotherapy target area delineation. At the same time, the application of diffusion sensitivity coefficient (b) and apparent diffusion coefficient (ADC) in DWI scanning also provides a basis for the determination of the nature of tissues and organs.
Geometric distortion caused by DWI imaging has always been an important technical index of clinical application. In this study, conventional DWI scanning and resolve HD diffusion scanning were applied to ACR phantom and 10 cases of rectal cancer. After analyzing the measurement results of geometric distortion, the accuracy requirements of image and the optimization of scanning parameters in clinical DWI application can be clearly obtained. Because the air cavity in the tissues and organs is the main factor to produce the geometric distortion of DWI, it is necessary to select appropriate strategies to reduce the impact during the simulation positioning, such as improving the gas-liquid interface, optimizing the conventional DWI scanning parameters, selecting the resolve HD diffusion scanning sequence, etc.
The application of MRI simulation equipment in radiotherapy is still in the initial stage. It is necessary to grasp the characteristics of MRI scanning sequence on the basis of clinical application to ensure safety and effectiveness. In this study, we designed and made a special calibration model for DWI sequence parameters, which can be widely used in clinical units.

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Keywords

Diffusion, MRI, Quality Assurance

Taxonomy

IM- MRI : Diffusion MRI

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