Lecture 9.1: Medical Visualization 1
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Applications
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Diagnosis (initial, continuing)
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Treatment planning (surgery, radiation)
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Training and Review
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Some Questions
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Where is the pathology and what is its relationship to the other parts of the ananatomy?
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Is there a fracture of the tibia?
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Has the pathological condition worsened?
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Is this the best location for a craniotomy?
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What is the volume of the tumor?
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How many lesions are there?
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Medical Visualization Pipeline
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Aquisition
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Resampling
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Segmentation and Classification
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Rendering
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Display
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Hazards of Visualization
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Adding visual richness and obscuring important detail
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Enhancing details incorrectly
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The picture is not the patient
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Prettier is better
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Data Sources
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Computed Tomography
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Basic Process
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Tomographic cross-sectional imaging
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X-ray beam in thin slice fan beam (collimation)
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Detector array placed opposite source tube (standard, spiral)
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Cross section reconstructed from the projections
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Artifacts
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Partial volume artifact -- voxels contain more than one tissue type
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Streak artifact -- streaks from motion, dental fillings
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Ring artifacts -- from miscalibration
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Beam hardening -- tissue filters beam
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Characteristics of CT
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axial slice 1-10 mm thick
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512 x 512 pixels, 0.5-2mm in size
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one second per slice with 4 seconds between slices
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low noise, high resolution
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contrast based on differential x-ray absorbtion
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consistent signal values, good spatial linearity
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moderate radiation dose
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Magnetic Resonance Imaging
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Basic Process
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Uses pulses of high-strength magnetic field
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Signal from resonation of tissue cells
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Different pulse sequences result in different responses from tissues
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Reconstruction phase involving Fourier analysis
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Typical study time = 30-45 min
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MRI Characteristics
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moderate noise, high resolution (voxels down to 1 mm)
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adaptable contrast
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inconsistent signal values
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inhomogeneous signal values
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poor spatial linearity
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no radiation dose
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Nuclear Medicine (SPECT, PET)
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patent ingests radiation source, detector catches radiation from body
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Characteristics
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moderate noise
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low resolution (pixels 5-10 mm)
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low contrast
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physiologically based signal
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few anatomic features
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moderate radiation dose
Ultrasound
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Basic Process
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transmit sound waves through body
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collect echoes
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reconstruct from reflections
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doppler shift based on motion of object or receiver
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Characteristics
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high noise
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moderate resolution, low contrast
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inconsistent signal values
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real time
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cheap
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no radiation does