Fig 1.
Two preclinical MR-CBCT imaging phantoms.
(a) Calibration phantom design (b) Geometry phantom design (c) 3D printed geometry phantom (d) Geometry phantom assembly. The cylindrical phantom was designed to fit within imaging and treatment cradles. The fillable compartments allow inclusion of materials such as water, air, silicone and glass to generate contrast.
Fig 2.
In-house designed MR-CBCT compatible cradle.
(a) computer-aided cradle design, (b) Preclinical MR scanning cradle, (c) PXI 225Cx CBCT simulation cradle.
Fig 3.
Experimental setup and Varian 4.7 T MR scanner.
(a) The animal was anesthetized using isoflurane and oxygen mixture for MR measurements and radiation treatment. (b) The animal’s vitals (respiratory and pulse oximetry) and temperature were monitored. (c) The animal was covered by a water-heated blanket to keep the temperature stable during MR measurement. (d) Varian 4.7 T MR scanner used in the study.
Fig 4.
(a) A CBCT-based workflow and (b) In-house MR-CBCT-based workflow.
Table 1.
The steps for manufacturer and in-house procedures.
Fig 5.
Length magnification in left-right (x-axis) and anterior-posterior (y-axis) directions and the area change along superior-inferior (z-axis) direction.
Fig 6.
Characterization of magnetic field distortion at 13 mm, 56 mm and 70 mm.
The cyan arrows represent the deformation vector fields (DVF). The red circles correspond to the original outline of the phantom in the MR images before correction, while the green circles correspond to the CBCT outline of the phantom.
Fig 7.
CBCT and MR geometry phantom images before and after applied correction.
Arrows point to noticeable geometric distortion.
Fig 8.
CBCT and the corresponding distortion corrected MR images.
(a) CBCT and (b) MR of the contouring and contrast modules. (c) CBCT and (d) MR of the grid module.
Table 2.
Grid size measurements before and after correction.
Fig 9.
(a) and (b) are the MR and CBCT data sets, respectively, used for co-registration. (c) MR structural features superimposed on the corresponding CBCT image labeled the CBCT+ dataset. (d) CBCT+ with the manually delineated planning target volume (PTV) contour. (e) CBCT image with PTV contour for final dose calculation and statistical analysis.
Fig 10.
PTV contours displayed on the distortion corrected fused MR-CBCT image.
Cyan represents PTV before correction, while pink depicts PTV after correction.
Table 3.
Tumor delineation blind test.
Fig 11.
Dose distribution and dose volume histogram for Rx of 60 Gy to 95% of PTV.
(a), (b), and (c) correspond to axial, sagittal, and coronal planes. A 15 mm circular cone was used for treatment planning and delivery. (d) DVH representation of PTV coverage.