Imaging Science Lecture 3.docx

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Western University
Medical Biophysics
Medical Biophysics 3503G
James Lacefield

3503 Imaging Science Lecture 3 January 16 th Contrast-Detail Analysis Continued o Hyperbola shape defined by two asymptotes • Detection Limited by Resolution o Vertical Asymptote; if you have a finer resolution, it will shift to the left o Features in the range between blue and red asymptotes are detectable by the finer resolution but not by the coarser resolution • Detection Limited by Local SNR o Diagonal Asymptote; if you increase the SNR, it will shift closer to the origin o Features in the range between the red and blue asymptotes are detectable by the higher SNR but not by the lower SNR • Realistic Contrast-Detail Curve • Contrast-Detail Comparison of Systems o Shows trade-off between resolution and SNR o If you want finer spatial resolution, you have to decrease your SNR and vice versa • Resolution vs. SNR Trade-off in Digital Mammography (Not tested on) • Interpretation of Contrast-Detail Curves Cancer triggers inflammatory processes that cause calcifications of healthy tissue around tumour Receiver Operating Characteristic (ROC) • This method was first developed for military applications with radar and sonar in WWII. • For realistic images instead of simplistic test images (Contrast-Detail) 1. Select one condition to detect or classify o Detect: Decide disease or healthy (Detect breast cancer) o Classify: Determine what the problem is 2. Image a large population including many individuals with and without disease 3. Choose ordinal (put them in order) parameter or criteria as basis for diagnosis o Objective: Size, contrast, etc. o Subjective: N-point indicating radiologist’s certainty about diagnosis (typically N-5). Ordinal: 1, 2, 3, 4, 5. 4. Perform gold standard diagnostic test (biopsy, blood sample, ECG, etc.) to obtain actual diagnosis for each patient o How well the result of the imaging exam matches the result of the gold standard test o We want the imaging test to agree with the g
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