Corrections within 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 Figure1 (Figure A) for the definition of Penumbra-Spread) causes blurring at the image edge-profile due to the size of the energy-source.
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 120 kVp,
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.
(1) MR breast tumor images (3D T1 W Fat suppression with Gadolinium enhancement (T1_3D_FS+GD)) was used for the study;
(2) CR image (first view) of...
Calibrations – Penumbra spread,
Penumbra spread = 2.4 pixels (or 1.30mm for pixel size = 0.54mm) across using a 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);
Area/Volume – At high-contrast & 1% low-contrast edge,
accurate to 1/18th & 1/10th of a pixel respectively in (delta)r (i.e.
(delta)(area) = 2(pi)r(delta)r (Volume = Area x Slice-thickness).
High-Contrast Resolution – Mean Modulation Transfer Function (MTF)...
The penumbra spread effect can not 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.
(1) coordinates of edge-profile may be fed into a mathematical model for oncological treatment monitoring &/or advanced physiological research study,
(2) in fracture bone healing progress monitoring to avoid any premature removal of support to pediatric fracture patient.
(1) "A De-Convolution Technique used for NDT in X-ray & CT".
K.M.Chui et al.,
Oral/Full paper presentation in 17th World Conference on Non-destructive Testing (17WCNDT),
(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".
Technical Inquiries – For technical inquiries or slide-set,
please contact Dr.
Kui Ming Chui at E-mail: firstname.lastname@example.org or via www.iet.org.uk.