Department of Medical Physics
Permanent URI for this collectionhttp://197.255.125.131:4000/handle/123456789/7530
Browse
2 results
Search Results
Item Ultrasound and Pet-Ct Image Fusion for Prostate Brachytherapy Image Guidance(University Of Ghana, 2015-06) Hasford, FFusion of medical images between different cross-sectional modalities is widely used, mostly where functional images are fused with anatomical data. Ultrasound has for some time now been the standard imaging technique used for treatment planning of prostate cancer cases. While this approach is laudable and has yielded some positive results, latest developments have been the integration of images from ultrasound and other modalities such as PET-CT to compliment missing properties of ultrasound images. This study has sought to enhance diagnosis and treatment of prostate cancers by developing MATLAB algorithms to fuse ultrasound and PET-CT images. The fused ultrasound-PET-CT image has shown to contain improved quality of information than the individual input images. The fused image has the property of reduced uncertainty, increased reliability, robust system performance, and compact representation of information. The objective of co-registering the ultrasound and PET-CT images was achieved by conducting performance evaluation of the ultrasound and PET-CT imaging systems, developing image contrast enhancement algorithm, developing MATLAB image fusion algorithm, and assessing accuracy of the fusion algorithm. Performance evaluation of the ultrasound brachytherapy system produced satisfactory results in accordance with set tolerances as recommended by AAPM TG 128. Using an ultrasound brachytherapy quality assurance phantom, average axial distance measurement of 10.11 ± 0.11 mm was estimated. Average lateral distance measurements of 10.08 ± 0.07 mm, 20.01 ± 0.06 mm, 29.89 ± 0.03 mm and 39.84 ± 0.37 mm were estimated for the inter-target distances corresponding to 10 mm, 20 mm, 30 mm and 40 mm respectively. Volume accuracy assessment produced measurements of 3.97 cm3, 8.86 cm3 and 20.11 cm3 for known standard volumes of 4 cm3, 9 cm3 and 20 cm3 respectively. Depth of penetration assessment of the ultrasound system produced an estimate of 5.37 ± 0.02 cm, indicating the system’s ability to visualize low contrast objects 5.4 cm into a patient. PET-CT system’s performance evaluation also produced satisfactory results in accordance with set tolerances as recommended by IAEA Human Health Series 1. Computed tomography laser alignment test ensured that all CT gantry lasers were properly aligned with the patient bed. Image display width test ensured that volume of patient or organ being measured and displayed was equivalent to that selected on the CT scanner console, to a deviation of ± 1 mm. Results from CT image uniformity test showed that mean CT numbers in peripheral regions of interest deviated from the central mean to within recommended tolerance level of ± 5 HU, indicating a good level of uniformity. Computed tomographic dose indices for head and body phantoms were estimated as 44.30 mGy and 20.08 mGy, comparative to console displayed doses of 42.40 mGy and 19.49 mGy respectively. Registration accuracy for PET-CT images was to have displacements of less than 1 mm in x, y and z directions. Image quality of PET-CT images was performed to produce images simulating those obtained in a total body imaging study involving both hot and cold lesions. Percentage contrast estimates of 49.3% and 52.6% were obtained for hot spheres of diameters 1.3 cm and 2.2 cm respectively, while contrast estimates of 74.8% and 75.6% were obtained for cold spheres of diameters 2.8 cm and 3.7 cm respectively. The PET-CT system resolution was estimated as 0.5 ± 0.01 cm, indicating the system’s ability to image tumours of the size of about 5 mm. Satisfactory results from the performance evaluation of ultrasound and PET-CT systems, paved way for them to be used in acquiring prostatic images for the study. Developed MATLAB image enhancement algorithm enhanced the quality of prostatic images before fusion. The algorithm was developed by mapping the intensity values in raw images to new values in a modified image using imadjust function. Contrast enhanced prostatic images of ultrasound and PET-CT were then co-registered with developed MATLAB fusion algorithm. The fusion algorithm was developed on the theory of mutual information and rigid body transformation. Fused image of ultrasound and PET-CT in this study has been assessed to have well defined and good visualized prostate capsule, urethra and implanted seeds, which would otherwise not be the case in either of the two images separately. The resultant image could therefore produce much more accurate results in treatment planning of prostate cancer cases. Assessment of image registration error for the ultrasound-PET-CT fused image produced a root mean square error estimate of 1.3 mm.Item Location of Radiosensitive Organs, Measurement of Absorbed Dose to Radiosensitive Organs and Use of Bismuth Shields in Paediatric Anthropomorphic Phantoms(University of Ghana, 2014-08) Inkoom, S.; Schandorf, C.; Fletcher, J.J.; University of Ghana, College of Basic and Applied Sciences Department of Medical PhysicsThe aim of this study was in two to investigate; firstly, (i) location of radiosensitive organs in the interior of four (4) paediatric anthropomorphic phantoms, and, secondly, (ii) effectiveness of single and double bismuth thyroid shields, distance between shield and phantom surface, during paediatric multi-detector computed tomography (MDCT) using fixed tube current (FTC) and automatic exposure control (AEC) on dose reduction and image quality. Four (4) paediatric anthropomorphic phantoms representing the equivalent of a newborn, 1-, 5-, and 10-y-old child underwent head, thorax and abdomen computed tomography (CT) scans. CT and magnetic resonance imaging scans of all children aged 0-16 y-old performed during a 5-y-period at the University Hospital of Heraklion, Crete, Greece were reviewed, and five hundred and three (503) were found to be eligible for normal anatomy. Anterior-posterior and lateral dimensions of twelve (12) of the above children closely matched that of the phantoms‟ head, thoracic and abdominal region in each four (4) phantoms. The mid-sagittal plane (MSP) and mid-coronal plane (MCP) were drawn on selected matching axial images of patients and phantoms. Multiple points outlining large radiosensitive organs and centres of small organs in patient images were identified at each slice level and their orthogonal distances from the MSP and MCP were measured. The outlines and centres of all radiosensitive organs were reproduced using the coordinates of each organ on the corresponding phantoms‟ transverse images. The four (4) phantoms were also subjected to routine head and neck, neck and thorax CT scans on a 16-slice CT system. Each phantom was first scanned with both FTC and AEC for with and without bismuth shields. Each scan was repeated ten (10) times to increase thermoluminescent dosimeters (TLDs) signal and reduce measurement statistical error. For neck CT, the effect of using single and double thickness of bismuth shields and 1-3 cm cotton spacers placed between the phantom surface and the shield on thyroid dose reduction and image quality was studied. Dose measurements were performed for each scan type using TLDs placed at internal locations in the phantoms and on the phantoms‟ surface. The thyroid organ and surface dose, eye lenses and breast surface dose were estimated separately. Anthropometric data of patients matching with the phantoms was used to locate each organ in the phantom slices. Effective dose was estimated by the dose-length product (DLP) method using specific normalised effective dose per DLP conversion factors for head, neck and thorax, by International Commission on Radiological Protection 103 recommendations. The location of the following radiosensitive organs in the interior of the four (4) phantoms was determined: brain, eye lenses, salivary glands, thyroid, lungs, heart, thymus, esophagus, breasts, adrenals, liver, spleen, kidneys, stomach, gall bladder, small bowel, pancreas, colon, ovaries, bladder, prostate, uterus and rectum. For head and neck CT scans, a maximum dose reduction of 44% / 34% (10-y-old) was achieved for thyroid surface / organ dose by FTC scanning. The use of AEC reduced the thyroid surface / organ dose compared with FTC to a maximum of 61% / 54% (5-y-old). The combined use of shield and AEC further reduced the thyroid surface / organ dose to a maximum of 79% / 68% (10-y-old). The 10-y-old phantom received the highest dose to the eye lenses (38.6 mGy) from head and neck CT for FTC, whilst 27.6 mGy was achieved for AEC scans. For neck CT scans, the use of single bismuth shield during FTC scanning reduced the thyroid surface dose to a maximum of 46% (5-y-old); whilst the thyroid organ dose was reduced to 35% (10-y-old). The use of double shields further reduced the surface dose to a maximum of 57% (5-y-old); whilst the thyroid organ dose was reduced to 47% (10-y-old). The activation of AEC reduced the thyroid surface dose to a maximum of 50% (5-y-old), whilst the thyroid organ dose was reduced to 46% (10-y-old). The combined use of single shield and AEC reduced the thyroid surface dose to a maximum of 70% (5-y-old); whilst the thyroid organ dose was reduced to 62% (10-y-old). The use of double shields and AEC activation further reduced the surface / organ dose to 76% / 65% (5-y-old). The maximum dose to the eye lenses due to neck CT was 7.0 mGy / 6.2 mGy (10-y-old) for FTC / AEC. The maximum breast dose attributable to neck CT was 0.6 mGy for 5-, and 10-y-old phantoms for all protocols. For thorax CT scans, the use of AEC induced a significant increase in the thyroid organ dose by a maximum value of 70% (1-y-old), and thyroid surface dose by 70% (newborn), and mean breast surface dose by 69% (newborn). The maximum increase of the effective dose as a result of application of AEC was 54% (newborn). In conclusion, the production of charts of radiosensitive organs inside paediatric anthropomorphic phantoms for dosimetric purposes was feasible. In-plane bismuth thyroid shielding decreases radiation dose in MDCT with/without deteriorating image quality. AEC was more effective in thyroid dose reduction than in-plane bismuth shields (head and neck CT, neck CT). AEC increased the absorbed dose to both the thyroid and the breast, as well as the effective dose in thorax CT. Thus, AEC should be abandoned as a dose optimisation tool during thoracic MDCT, especially in neonates, infants and children younger than 10-years-old. Placement of the spacer between shield and surface had no significant impact on the measured doses, but significantly decreased the image noise.