Influence of acquisition time and smoothing parameters on Ga-68 wholebody PET/CT image quality

Diale, Boitshoko Phenyo (2020-12)

Thesis (MSc)--Stellenbosch University, 2020.

Thesis

ENGLISH SUMMARY : PET/CT image optimization has been extensively investigated for 18F–FDG PET imaging. Although 68Ga–tracers are already widely used in PET, optimized imaging and reconstruction are still missing. The aim of this research was to optimize image quality for 68Ga scans under the constraint that the administered dose to a patient and acquisition time are limited. Materials and Methods : A Gemini TF Big Bore PET/CT system manufactured by Philips was used to acquire the images. The experimental data was formulated by retrospectively collecting data from patient scans, who had undergone wholebody (WB) PET/CT using 68Ga–DOTANOC for oncological imaging. The patient data sets were analyzed for this study to plan phantom measurements which simulated a typical activity distribution like in the patient scans. The NEMA (IEC) body phantom filled with low contrast and high contrast activity ratios was scanned on the Gemini TF Big Bore PET/CT scanner using the patient acquisition protocol. The data was reconstructed using a default WB reconstruction protocol with different smoothing parameters and varying scan acquisition times for low and high contrast data. Additionally a HN protocol with smaller voxel sizes was also used on high contrast data. The set images were analyzed using R Studio. Image quality parameters such as coefficient of variation (COV%), contrast to noise ratio (CNR), signal to noise ratio (SNR), recovery coefficient (RC%) and uniformity in terms of standardized uptake value (SUV) were acquired. Results: For low contrast COV%, CNR, SNR values varied as follows: 0.89 – 0.99%, 0.96 – 1.08, 0.99 – 1.05, respectively. Values for high contrast varied as follows: 1.03 – 1.16%, 0.84 – 0.91, 0.80 – 0.97. When comparing COV%, CNR and SNR, low contrast images appeared to be superior to high contrast images. The RC% was found to be consistent in both low contrast and high contrast irrespective of the smoothing parameter. Conclusion: The results obtained from the phantom study demonstrated the Philips Gemini TF Big Bore PET scanner’s stability of good uniformity when assessing maximum activity concentration among the different acquisitions, and ability of the scanner to detect or recover radioactivity in low and high contrast images for all reconstruction parameters. From the phantom study results, incorporating the smoothing reconstruction parameter ”smooth” on low contrast images, allowed the reduction of acquisition time to 180 seconds while maintaining acceptable image quality.

AFRIKAANSE OPSOMMING : Optimale beeldkwaliteit van PET/RT beelding is vir 18F–FDG PET beelding reeds in diepte ondersoek. Alhoewel 68Ga–spoorders reeds algemeen in PET gebruik word, is daar steeds ’n leemte in die daarstelling van optimale beelding en rekonstruksie parameters. Die doel van hierdie navorsing was om beeldkwaltiteit van 68Ga skandering te optimaliseer met die inagneming van beperkings in die toegediende dosis en beeldingstyd Materiaal en Metodes: ’n Philips Gemini TF Big Bore PET/RT kamera is vir beelding gebruik. Die eksperimentele data is beplan deur retrospektief data van onkologiese heeliggaam (HL) 68Ga–DOTANOC PET/RT studies te versamel. Hierdie data is geanaliseer om fantoommetings te beplan wat tipiese verspreiding van aktiwiteit in pasientstudies sou simuleer. ’n NEMA (IEC) liggaamsfantoom is met lae en hoe kontras aktiwiteitverhoudings gevul en vervolgens, volgens die bestaande pasi entbeeldingsprotokol, met die Gemini TF Big Bore PET/RT kamera skandeer. Die data is met ’n verstek HL rekonstruksieprotokol met verskillende vergladdingsparameters en vari erende beeldingstye vir lae en hoe kontrasdata verwerk. Bykomend is ’n kop–en nek–protokol met kleiner vokselgrootte op hoe kontrasdata ook gebruik. Die beelde is met R studio geanaliseer. Beeldkwaliteitparameters soos variasiekkoeffisient (COV%), kontras tot geraas verhouding (CNR), sein tot geraas verhouding (SNR), herstelko effisi ent (RC%) en uniformiteit in terme van gestandardiseerde opname waarde (SUV), is verkry. Resultate: Vir lae kontras het COV%, CNR, en SNR waardes respektiewelik soos volg gevarieer: 0.89–0.99%, 0.96–1.08, en 0.99–1.05. Waardes vir ho e kontras het soos volg gevarieer: 1.03 – 1.16%, 0.84–0.91, en 0.80–0.97. As COV%, CNR en SNR vergelyk is, was lae kontras beelde beter as ho e kontras beelde. Die RC% was konstant in beide lae kontras en hoe kontras, ongeag die vergladdingsparameter. Gevolgtrekking: Die resultate van die fantoomstudie het die Philips Gemini TF Big Bore PET skandeerder se stabiele uniformiteit, in die evaluering van maksimum aktiwiteit konsentrasie tydens verskillende beeldverkrygings, bevestig. Dit het getoon dat die skandeerder in staat is om radioaktiwiteit in lae en hoe kontrasbeelde, vir alle rekonstruksieparameters, waar te neem. Volgens die resultate van die fantoomstudies kan die beeldingstyd tot 180 sekondes verkort word, as die verwerkingsparameter ”glad” (smooth) in die lae kontras beelding gebruik is.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/109341
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