3D Augmented Reality for MRI-Guided Surgery Using Integral Videography Autostereoscopic Image Overlay Hongen Liao, Takashi Inomata, Ichiro Sakuma and Takeyoshi Dohi Presented by Zhenzhou Shao 2/24/2011

Outline Introduction Material and Methods Experiment and Results System Configuration IV Image Display and Overlay Device Registration of Spatial 3D Image in Patient Software Alignment Surgical Procedure Experiment and Results Conclusion

Introduction Magnetic resonance imaging (MRI) A medical imaging technique Provides detailed information about soft tissue. The obtained images are used to accurately identify treatment areas by acquiring pre-/intraoperative information and updating it to a navigation system used in MRI-guided surgery. A strong magnetic field is created. protons in the body to align themselves. radio waves are absorbed by the protons with the same frequency, and protons will be raised to a higher state of energy. When the radio signal is turned off, after a period of time, the protons will return to their original energy state. The extra energy is received by the sensors in the scanner, then sent to a computer which processes all the signals and generates it into an image

Introduction Potential efficacy using MRI-guided surgery Advantages Enhance the surgeon’s capability Decrease the invasiveness of surgical procedure Increase the accuracy and safety Disadvantages Display of a set of 2D sectional images Hand–eye coordination problem Repetitive look away from the patient The surgeon had to reconstruct 3-D information in their mind. However, the reconstructed information sometimes differs between individual surgeons.

Introduction Augmented Reality (AR) Superimpose the virtual model into the real scene. Video see-through AR Head mounted display (HMD) Limited field of view A lag for motion parallax Cannot provide a natural view for multiple observers

Introduction Optical see-through AR Using a semi-transparent mirror for merging virtual model with a direct view. Surgeon can see through the body. Enhance the surgeon’s ability to perform a complex procedure. Depth information is required.

Introduction Integral Videography(IV) Figure 1 shows the principle of IV. Each point in a 3-D space is reconstructed by the convergence of rays from pixels on the computer display through lenses in the array. The observer can see any point on the display from various directions as if it were fixed in 3-D space. IV can display animated 3-D objects, and it also has the merits of IP.

System Configuration

IV Image and Overlay Device

Registration of 3D Image in Patient

Registration of 3D Image in Patient Project an IV image of a spatial calibration model with special calibration points and reflect the image into 3-D space via the half-slivered mirror

Registration of 3D Image in Patient

Registration of 3D Image in Patient

Software Alignment

Surgical Procedure Calibrate the position of reflected IV image; Place sterile fiducial markers on the surface of the patient’s body and scan the target area; Segment the target of interest and markers from the MRI data. Perform patient-to-image registration to find the ;

Surgical Procedure Render the IV images and transfer them to the overlay device; Perform the surgical treatment under the guidance of IV image overlay; After finishing the treatment, translate the patient into the scanner again and confirm surgical result.

Experiment and Results Accuracy measurement Implemented by using markers in a phantom simulating the human head.

Accuracy measurement Five markers for registration and two for error measurement. Marker: 10 mm in external diameter and 3 mm in internal diameter. The distance between the center of the actual marker and that of the spatial projected IV marker was measured as an overlay error. The mean value of the error was 0.90 mm, and the standard deviation was 0.21 mm

Targeting Experiment Compare the procedure time and success rate of targeting an object using 2-D image guidance and IV overlay system guidance. Phantom consisted of a plastic cube container filled with an agar.

Targeting Experiment Six MRI markers were attached. Three sets of acrylic cylinders with diameters of 1.5, 2 and 3 mm were embedded within the phantom.

2-D image guidance four operators for each of ten trials

IV overlay system guidance

Results of guidance 2-D image guidance IV overlay system guidance

Comparison of procedure time

Feasibility Evaluation Evaluate the feasibility by a volunteer test. Scan brain using MRI. Motion parallax could be generated due to the motion of an observer. The motion parallax of IV autostereoscopic brain images combined with the volunteer’s head was taken from various directions.

Feasibility Evaluation

In Vivo Animal Experiment Target a pig’s gallbladder. A set of markers was attached to the skin of the surgical area.

In Vivo Animal Experiment Surgical planning to minimizing the surgical exposure. Surgical instrument is tracked. The targeting experiment was performed by a medical doctor. The result shows that the developed intraoperative IV image overlay technique with corresponding image registration can improve surgical navigation by providing a direct and intuitive view of the operation field. In combination with robotics, it can even supply guidance by predefining the path of a needle or by preventing the surgical instruments from moving into critical regions.

Conclusion An autostereoscopic image overlay system for MRI-guided surgery is developed. IV is employed to provide accurate 3-D spatial images and reproduces motion. A fast and accurate spatial image registration method was developed. Safe, easy, and accurate surgical diagnosis and therapy.

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