Surface Contour Registration for CT-Less Free-Breathing Radiotherapy
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Solution Overview
Problem
Current radiation treatment systems require two CT scans to capture deep inspiration breath-hold (DIBH) and free breathing (FB) contours, which is inefficient and increases ionizing radiation exposure, especially as many hospitals now only perform CT scans in DIBH.
Innovation Solution
A method using a surface camera to capture images during both breathing conditions, transforming the FB contour into the DIBH coordinate system through image fusion with CT data, eliminating the need for additional ionizing radiation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a CT scan is performed to acquire the free breathing contour, then the contour accuracy is improved, but the ionizing radiation exposure increases
Solution Approach 1:
The patent uses a surface camera to capture optical images of the patient's chest surface, creating a visual copy of the external anatomy. This optical copy is then registered with the CT data to derive the free breathing contour without exposing the patient to additional ionizing radiation, thereby maintaining measurement precision while eliminating the harmful effect
Solution Approach 2:
The patent replaces the mechanical/physical CT scanning process with an optical imaging system (surface camera). Instead of using ionizing radiation to capture the contour, the system uses visible light to photograph the patient's surface, substituting a harmful physical process with a benign optical one while still achieving the required contour accuracy
2Measurement precision
If two separate CT scans are performed (one for DIBH contour and one for FB contour), then both contour measurements are improved, but the measurement time and procedure complexity increase
Solution Approach 1:
The patent merges the acquisition processes by capturing both DIBH and FB surface images using the same surface camera system. The DIBH contour is obtained from the CT scan while the FB contour is obtained from a separate surface photograph taken during free breathing, eliminating the need for a second CT scan and reducing overall measurement time
Solution Approach 2:
The surface camera system serves multiple functions: it captures both DIBH and FB surface images, provides real-time visual feedback for patient positioning, and enables contour extraction without requiring separate specialized equipment for each breathing state, thereby improving efficiency while maintaining measurement precision
3Object-affected harmful factors
If a surface camera is used to capture the free breathing contour, then the ionizing radiation exposure is reduced, but the spatial alignment accuracy with CT data may worsen
Solution Approach 1:
The patent introduces an intermediary registration process that uses anatomical landmarks and surface geometry features to align the optical image coordinate system with the CT coordinate system. This intermediary step ensures accurate spatial transformation between the two different imaging modalities, maintaining measurement precision while using the non-ionizing surface camera
Solution Approach 2:
The patent transforms the 2D surface camera images into 3D surface models through photogrammetric processing. This dimensional transformation allows for more accurate spatial registration with the 3D CT data by utilizing depth information and surface curvature, thereby achieving precise alignment without requiring additional ionizing radiation
Data Source
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AI summary
Disclosed is a method of transforming a first medical image dataset describing an anatomical body part of a patient into a reference system of a second medical image dataset describing the anatomical body part. The method encompasses taking images of a surface of an anatomical body part during both free breathing and deep inspiration breath-hold using a surface camera as well as a tomography such as a CT of the anatomical body part during deep inspiration breath-hold. Contours are extracted from the surface camera images and the tomography representing a contour of the anatomical body part such as a surface of the patient's thorax. The contour extracted from the camera image taken during free breathing is transformed into a coordinate system used for defining positions in the tomograph (i.e. a coordinate system used by the tomograph used for generating the tomography) by fusing the contour extracted from the tomography with the contour extracted from the deep inspiration breath-hold camera image and applying the transformation representing the fusion result to the camera image taken during free breathing. (Figure 3)