Digital Radiology
X-ray is one of the most important medical imaging techniques. Currently, X-rays are produced using a phosphor screen coupled to a photographic film for readout. There are fundamental (image quality) as well as practical (cost, convenience and co-ordination) problems with this approach. The fundamental problems can be tackled by the use of direct conversion systems based on solidstate semiconductors e.g. amorphous selenium. The practical problems can be addressed by use of digital systems that readout the X-ray image electronically.
In static X-ray imaging ("radiography"), three readout approaches are being investigated based on active matrix, liquid crystal or laser readout for applications in chest imaging, general radiography and mammography.
For dynamic X-ray imaging ("fluoroscopy") we are replacing conventional X-ray image intensifiers either with an active matrix flat panel device modified to include one of three innovative approaches: avalanche multiplication in selenium, intelligent pixels or a novel photoconductor - mercuric iodide. The primary application area is in cardiac imaging where we are also looking at combining X-ray with MRI.
For imaging during radiation therapy (portal imaging) the image quality needs to be improved radically before it can be clinically relevant. We are planning to improve the detection efficiency of the sensor by almost two orders of magnitude, which should reduce noise by an order of magnitude. Understanding the physical limits of our systems will permit optimally matching them to clinical applications. Our investigations are resulting in improved clinical devices.
Graduate Students:
- Sarah Cuddy
Selected References:
Link to Pubmed Publications-
JA Rowlands, “Physics of computed radiography”, 2002 Physics in Medicine and Biology 47: R123-R166
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D Hunt and JA Rowlands, 2002 “Avalanche multiplication and conversion gain in amorphous selenium” Medical Physics 29: 2464-2471
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R Fahrig, K Buttes, JA Rowlands, R Saunders, J Stanton, GM Stevens, BL Daniels, Z Wen, DL Ergun and NJ Pelc, 2001 A truly hybrid interventional MR-X-ray system: feasibility demonstration. Journal of Magnetic Resonance Imaging, 13: 294-300.
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G Pang, DL Lee and JA Rowlands, 2001 Investigation of a direct conversion flat panel imager for portal imaging, Medical Physics, 28: 2121-2128.
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W Zhao, IM Blevis, DF Waechter, Z Huang and JA Rowlands. 1997 Digital radiology using active matrix readout of amorphous selenium: Construction and evaluation of a prototype real-time detector. Medical Physics 24: 1834-1843.
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Pia-Krista Rieppo and JA Rowlands. 1997 X-ray imaging using amorphous selenium: Theoretical feasibility of the liquid crystal light valve for radiography. Medical Physics 24:1279-1292. JA Rowlands and DM Hunter. 1995 X-ray imaging using amorphous selenium: Photo- induced discharge (PID) readout for digital general radiography. Medical Physics 22:1983-1996.
