The effect of digital and physical filters on image quality for quantitative Tc-99m single photon emission computed tomography (SPECT).

Pengukuran kuantitatif dilakukan menggunakan data SPECT untuk mengukur saiz dan menganggar jumlah aktiviti radionuklid di dalam sesuatu organ atau lesi. Foton terserak pada imej merupakan masalah utama untuk memperolehi pengukuran kuantitatif yang tepat. Tujuan kajian ini dilakukan adalah untuk mengkaji kesan penuras fizikal terhadap kualiti imej di dalam pengimejan kuantitatif SPECT. An absolute quantitation can be made on SPECT data to accurately measure the volume and estimate total radionuclide activity in the organ or lesion. The major problem to produce an accurate quantitation is the contamination of SPECT images by scattered photons. The aim of the study is to investigate the effect of physical filters on image quality in quantitative SPECT imaging

Investigation of Personalised Post-Reconstruction Positron Range Correction in 68Ga Positron Emission Tomography Imaging

Positron range limits the spatial resolution of Positron Emission Tomography, reducing image quality and accuracy. This thesis investigated factors affecting the magnitude of positron range, developed a personalised approach to range correction, and demonstrated the approach using simulated, phantom and patient data. The Geant4 Application for Emission Tomography software was utilised to model positron range when emitted by radionuclides, namely 18F and 68Ga, in water, bone and lung. The impact of range blurring in lungs was found to be ten times larger than in bone and four times larger than in water or soft tissue, regardless of the positron energy. Range effects occurring with different isotopes (18F and 68Ga) were evaluated across measurement and reconstructed spatial resolutions. It was found that range correction was not necessary when using 18F for voxel sizes larger than 4 mm. In contrast, range correction was required for images generated using 68Ga, particularly within or adjacent to the lung. An iterative, post-reconstruction range correction method was developed which relied only on the measured data. The correction method was validated in both simulation and phantom studies. Image quality and quantification accuracy of corrected images was shown to be superior when imaging with 68Ga. Importantly, the range correction suppressed and controlled image noise at high iteration numbers. Finally, in a patient study, image noise in regions of uniform uptake was significantly increased by ~2% (p<0.05), yet mean standardised uptake values remained unchanged after correction, showing the same uptake for normal radionuclide distributions. The lesion contrast and maximum uptake values were improved by 20% and 45%, respectively with statistical significance (p<0.05). Although these promising results show that the proposed method of range correction can be generalised to reconstructed images regardless of measurement system, acquisition parameters and radionuclides used, further research is warranted to improve the method, particularly with respect to removing or reducing the artefacts which were shown to impacted reader preference

Penilaian dos sinaran ke atas gonad dan tiroid semasa prosedur PET-CT

Gonad dan tiroid merupakan organ radiosensitif yang memerlukan pelindung sinaran untuk mengurangkan dos yang diterima. Walau bagaimanapun, pelindung sinaran tidak digunakan secara meluas dalam pengimejan radionuklid kerana ianya berat, kurang selesa dan boleh mendatangkan kesakitan pada tulang belakang. Oleh itu, penyelidikan ini dijalankan untuk mengetahui keupayaan pelindung sinaran gonad dan tiroid yang lebih nipis dan ringan dalam mengurangkan dos sinaran. Satu kajian telah dijalankan di Hospital Putrajaya untuk menentukan dos sinaran yang diterima oleh tiroid dan gonad semasa prosedur lengkap Tomografi Pancaran Positron-Tomografi Berkomputer (PET-CT) dengan dan tanpa pelindung sinaran. Seramai 6 orang kakitangan lelaki telah dipilih sebagai subjek dan data daripada 33 prosedur lengkap PET-CT telah dikumpulkan. Untuk setiap prosedur PET-CT, tiroid dan gonad subjek masing-masing dilindungi menggunakan pelindung sinaran berketebalan 0.5 mm model Mavig 615 (USA) dan Shielding International (USA). Cip dosimeter pendarkilau terma (TLD) digunakan sebagai pengesan dos sinaran.Purata radioaktiviti 18F-FDG yang disuntik ke dalam pesakit adalah 387 MBq dan purata tempoh imbasan adalah 9.224 ± 1.797 minit. Keputusan menunjukkan purata dos setara yang diterima oleh tiroid dengan dan tanpa pelindung adalah masing-masing 0.080 ± 0.033 mSv dan 0.078 ± 0.039 mSv. Purata dos setara yang diterima gonad dengan dan tanpa penggunaan pelindung pula adalah masing-masing 0.059 ± 0.040 mSv dan 0.061 ± 0.030 mSv. Pelindung sinaran berketebalan 0.5 mm tidak berupaya mengurangkan dos sinaran yang diterima oleh tiroid (p = 0.76) dan gonad (p = 0.79) akibat terlalu nipis untuk menahan sinaran bertenaga tinggi semasa prosedur PET-CT. Tiroid menerima dos sinaran yang lebih tinggi sebanyak 0.016 mSv berbanding gonad (p < 0.05) kerana kedudukan tiroid yang lebih terdedah kepada sumber sinaran iaitu 18F-FDG semasa penyediaan radiofarmaseutikal tersebut dan pesakit yang sudah disuntik 18F-FDG semasa prosedur PET-CT