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Image Quality in Different Modalities of Medical Imaging with Focus on Mammography. Dr. Nabil Maalej Physics Dept., KFUPM 14-12-2004. Outline. Imaging Modalities (Brief) Image Formation in Mammography Image Quality Contrast Resolution Image Quality Assurance
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Image Quality in Different Modalities of Medical Imaging with Focus on Mammography Dr. Nabil Maalej Physics Dept., KFUPM 14-12-2004
Outline • Imaging Modalities (Brief) • Image Formation in Mammography • Image Quality • Contrast • Resolution • Image Quality Assurance • Image Enhancement and Computer Aided Diagnosis (Examples)
X-ray Production X-rays are produced in a vacuum tube that accelerates electrons across a high voltage in the order of 100,000 volts. The accelerated electrons strike a target made of tungsten and produce X-rays.
X-ray Pictures Chest X-ray Head X-ray
Digital Angiography It is a diagnostic procedure that produces X-ray pictures of blood vessels. A catheter is inserted in the vessel to inject contrast fluid into the lumen of the blood vessel, which then becomes visible on X-ray images.
Digital Angiography Images Digital Subtraction Angiography (Mistretta, 1980s)
Computerized Tomography (CT) The technique of CT scanning was developed in 1973 by Hounsfield. A thin fan beam of X-rays generated by a conventional X-ray tube passes through a single 'slice' of a patient through to a bank of X-ray detectors.
CT 2-D Images CT Scan of the Abdomen 3-D CT Image of the Head
Diagnostic Ultrasound Ultrasound is a technique for visualizing internal structures in the body using sound waves.
Ultrasound Images Image of the Heart Image of a Fetal Heart
Magnetic Resonance Imaging The technique involves placing the patient in a strong magnetic field. The magnetic field aligns the nuclear spin of atoms in the patient. When the spins relax to the original orientation, they emit radio-waves which are picked up by receiver coils.
Magnetic Resonance Imaging 2-D MRI scan of the brain Functional MRI of The Brain
Image Formation In Mammography
Breast Cancer (Highest) • For the total Saudi population, the most common ten cancers are (1994-1996 Cancer Registry): • Female breast cancer (8.8%), • Liver cancer (7.5%), • Leukemia (7.5%), • Non-Hodgkin's lymphoma (7.3%) • Colo-rectum cancer (5.5%). • Thyroid cancer (5.2%), • Lung cancer (4.7%) • Nervous system cancer (3.9%) • Stomach cancer (3.8%) and • Urinary bladder cancer (3.5%)
Problem in Detection • False negatives: 10-30% of the visible cancers go undetected • False positives: 70-85% of biopsies unnecessary.
What Can We do to Get Best Image? X-ray Source X-ray Beam Compression Paddle Compressed Breast Table Chest Wall Grid Image Detector
IMAGE QUALITY
Imaging Quality Parameters CONTRAST RESOLUTION NOISE
Contrast • Image Contrast is a measure of difference between regions in an image • Image contrast in mammography is due to the difference in linear attenuation coefficient and thickness of different types of tissue
Attenuation Coefficient Contrast decreases toward higher energies the recommended optimum for mammography is in the region 18 - 33 keV depending on tissue thickness and composition.
I I Ib Ib It It S Contrast Degradation with Scatter
Anti-scatter grid breast leadsepta detector
Resolution • Spatial resolution of an imaging system can be defined in terms of the smallest spacing between two objects that can be imaged clearly • Example for Radiography spatial resolution is about 0.01 mm, for CT it is about 1 mm • Good resolution is essential to see micro-calcifications in a mammogram
IMAGE QUALITY ASSURANCE
Contrast Detail Analysis • Contrast detail analysis: an observer reports the size of the smallest object he or she can perceive at a certain contrast level and with a given noise level in the image.
RMI 156 Phantom ACR minimum score is 4 visible fibers, 3 speck groups and 3 masses
Image Enhancement
Digital Mammography Systems • The Fischer Imaging System: 54 m/pixel, a matrix size of 3,072 x 4,800 pixels, 12 bits/pixel • The GE Medical Systems: 100 m/pixel and a matrix size of 1,800 x 2,304 pixels, 14 bits/pixel • The Trex Medical 41 m/pixel and a matrix size of 4,800 x 6,400 pixels, 14 bits/pixel
Image Enhancement • Single Point Processing • Pixel Group Processing • Frequency Domain Processing • Deconvolution • Geometric Transformation • Other Transformations (FT, Wavelet, …
Manual Intensity Windowing (MIW) • A small portion of the full intensity range of an image is selected and then remapped to the full intensity range of the display device • allow exaggeration of small differences in intensity values between the two objects • It is operator dependent
Histogram-Based Intensity Windowing (HIW) • Intensity windowing allows a selected subrange of the image intensity values to receive the full contrast of the display device • statistically analyzing the histogram of each image, locating the modes that represent the different breast tissue types (fatty, dense, muscle) or other parts (background). • intensity window range is automatically selected on the basis of the percentile position within the composite breast tissue class
Mixture-Model Intensity Windowing (MMIW) • MMIW provides region-specific intensity window settings for mammograms • It automatically identifies the five major regions in a mammogram: background, uncompressed fat, compressed fat, dense tissue, and muscle • A specific region histogram can be selectively analyzed to determine region-specific intensity window settings • The mean and standard deviation of the intensities in the region are used to parameterize a sigmoidal intensity window function
Mixture-Model Intensity Windowing (MMIW) MMIW (Dense Tissue)
Unsharp masking • low-pass filtered version of the original image is created and the image values that result are subsequently multiplied by a weighting factor and subtracted from the original image