Purpose
Corrections within the processing software such as the Back-Projection Algorithm (for CT or NM/PET) or the Fast Fourier Transform (for MRI) are unable to overcome or remove the century-old Penumbra Effect. But this effect may be overcome by the following post-processing Computer Aided Detection (CAD) algorithm.The Penumbra-Effect (refer to Figure 1 (Figure A) for the definition of Penumbra-Spread) due to the size of the energy-source causes blurring at the image edge-profile. A CAD software based on the De-convolution Technique can be used to pinpoint the...
Methods and Materials
(I) Phantom-Calibrations - A New York Catphan 500 was examined using Single Slice helical CT using technique factors of 120kVp, 300mA, 4 secs., 10mm slice.Penumbra Spread, distance, area/volume, high-contrast resolution, and processing time were measured:Coin & Wire Phantom was also used to study the removal of Penumbra Effect at the edges of a Guide Wire.(II) Six Field-Studies:-63 year old male patient was knee scanned by CT at: 120kVp; 150mA; 1.4 s/slice; Slice-thickness=1.25mm;Fracture radius bone of the forearm of a 25 year old male patient was...
Results
Calibrations – Punumbra-spread, Distance, Area/Volume Accuracies-Punumbra-spread = 2.4 pixels (or 1.30mm for pixel size=0.54mm) across using an 1.2mm X-ray tube-spot.Distance – At high-contrast & 1% low-contrast edge, both accurate to 1/50th of a pixel in (delta)r (i.e. (delta)r in (delta)r/r);and,Area/Volume – At high-contrast & 1% low-contrast edge, accurate to 1/18th & 1/10th of a pixel respectively in (delta)r (i.e. 2(pi)r(delta)r/(pi)r2 or(delta)(area) = 2(pi)r(delta)r (Volume = Area x Slice-thickness).High-Contrast Resolution – Mean Modulation Transfer Function (MTF) (Ref. 2) at the high-contrast edge were improved from 3.38...
Conclusion
The Edge Response Function blurring or the 'penumbra spread' cannot be overcome by current digital enhancement as its true edge position is not located. But this deconvolution technique permits sensitive and accurate edge-profile detection and enhancement to overcome the century old 'penumbra spread' problem without any trade-off loss.Invisible and barely visible minute bone fractures were enhanced to clearly visible for accurate diagnosis and measurements for the quantitative 4D assessment of bone fracture healing progress in orthopedics.Streaking artifacts were overcome via the selective enhancement of high-contrast...
References
(1) "A De-Convolution Technique used for NDT in X-ray & CT", by K.M.Chui etal., Oral/Full paper presentation in 17th World Conference on Non-destructive Testing (17WCNDT), Shanghai, China, October 25-28, 2008. (NDT.net - The e-Journal & Database of Nondestructive Testing - ISSN 1435-4934.).(2)"The line spread function and modulation transfer function of a computed tomographic scanner", by Judy P.F.,Med. Phys. Vol.3, No. 4, Jul/Aug. 1976, pp.233-236.
Personal Information
1) Technical Inquiries - For technical inquries, please contact Dr. Kui M. Chui at E-mail:
[email protected] or
[email protected] or via www.iet.org.uk ;and,2)Power-Point Slide Set - to obtain a copy of the slide-set (with animated view), please contact Dr. Kui M. Chui at E-mail:
[email protected] or
[email protected] or via www.iet.org.uk.