Comparison of image quality and standardized uptake values (SUV) of two PET/CT imaging system using F-18 and Ga-68

Both the Gemini TOF PET/CT and Biograph mCT flow PET/CT scanners are advanced imaging systems used in clinical settings for a range of applications, including oncology, neurology, and cardiology. Both the Gemini TOF PET/CT and Biograph mCT flow PET/CT scanners are advanced imaging systems used in clinical settings for a range of applications, including oncology, neurology, and cardiology. Both systems are capable of producing high quality images with good spatial resolution and contrast. However, there are some differences between the two systems that may impact image quality. The recovery coefficient (RC) is an important parameter that is used to evaluate the image quality and the accuracy and precision of PET/CT imaging systems. In the other hand, Standardized uptake value (SUV) is A frequently utilized quantitative measure in PET/CT imaging is the estimation of radiotracer uptake within a specified region of interest (ROI). SUV measurements are possible to be used to assess tumor metabolism and monitor treatment response. Several studies have evaluated the SUV and RC measurements using different radiotracers and scanner has been found to exhibit good accuracy and precision for both radiotracers. In this work we investigated the SUV and RC values of the Gemini TOF PET/CT and Biograph mCT flow PET/CT scanners by using F18 and Ga-68 and compared their values. Methods in this work, we analyzed images acquired using two distinct PET-CT scanners from two different manufacturers; Gemini TOF PET/CT (Philips Medical Systems) system and biograph mCT flow PET/CT system (Siemens Healthineers). we assessed the SUV values by using the PET-CT cylindrical image quality NEMA phantom that was filled with F-18 and Ga-68 while the image quality measured by employing the NEMA/International Electrotechnical Commission (IEC) Torso Phantom. Results We revealed that the RC values of F-18 using Gemini TOF PET/CT ranged from 0.02 to 0.03 for different sphere sizes, where they ranged from 0.005 to 0.015 for Ga-68 and when used Biograph mCT flow PET/CT scanner RC values of F-18 ranged from 0.025 to 0.05 and for Ga-68 ranged from 0.02 to 0.042. The first section in your paper


Introduction
Positron Emission Tomography (PET) is a highly effective imaging technique that enables the examination of the temporal distribution of positron emitter-labeled radiopharmaceuticals in vivo.This technique has been shown to improve the detection and staging of malignant tumors, leading to more accurate diagnoses and optimal treatment planning [1].Imaging techniques that utilize positron emission tomography (PET) combined with computed tomography (CT) or magnetic resonance imaging (MRI) have demonstrated superior efficacy compared to conventional imaging modalities like CT and MI, and somatostatin receptor scintigraphy (SRS) in several clinical applications.For example, in the diagnosis of lung cancer, Studies have shown that PET/CT has superior sensitivity and specificity in comparison to CT alone, leading to improved accuracy in staging and treatment planning [2].In the case of head and neck cancer, PET/CT has been shown to have higher accuracy than MRI in detecting nodal metastases, leading to more appropriate treatment decisions [3].In neuroendocrine tumors, PET/CT with Ga-68-DOTA peptides has been found to be more accurate than SRS for lesion detection and staging [4].Similarly, PET/CT demonstrates greater sensitivity and specificity than conventional imaging in the detection of recurrent colorectal cancer [5].
The PET image quality depends on a number of factors including the radiopharmaceutical properties, the quantity of administered activity, imaging protocol, reconstruction methods, attenuation and scatter correction, image processing and the scanning acquisition time.Patient characteristics, such as body size, tissue composition, and patient motion, can also affect PET image quality.It should also be considered that the amount of attenuation and scatter radiation induced by the size of the patient might impact the image quality [6] [7].
The Standardized Uptake Value (SUV) is a quantitative measurement used in PET imaging to describe the degree of radioisotope uptake in a particular region of interest.SUV is calculated by dividing the tissue concentration of the radiotracer by the injected dose of the tracer normalized to the patient's body weight.The resulting value is a dimensionless ratio that reflects the amount of tracer uptake per unit of tissue volume, it is a mathematically derived ratio between the tissue radioactivity concentration at a given time C(T) and the injected dose of radioactivity per kilogram of patient body weight: SUV = C(T)/ [injection dose (MBq)/patient's weight (kg)] (1.1) SUV is a commonly used metric in PET imaging because it provides a quantitative measure of the tracer uptake that can be used to compare uptake in different regions of interest or between different patients.SUV can also be used to monitor changes in tracer uptake over time, which can be useful for assessing treatment response or disease progression.However, there are limitations to the use of SUV as a quantitative measure.SUV is affected by a number of factors, including the patient's body weight, the injected dose of the tracer, and the timing of the PET scan relative to tracer injection.As a result, SUV can be affected by variability in these factors, which can limit its accuracy and reproducibility.Despite its limitations, SUV remains a widely used metric in PET imaging, particularly in clinical settings where it provides a simple and convenient measure of tracer uptake.Careful consideration of the factors that can affect SUV measurements, such as patient body weight and imaging protocol, is important to ensure accurate and reliable results [8] [9].

Radionuclides
Several radiotracers are currently available for the investigation of PET studies.18F is the most widely utilized PET radionuclide, it is produced by cyclotron, and it is the standard isotope used in PET imaging system.On the other hand, generators can also be used to create positron emitting radionuclides, such as the 68Ge/68Ga, 82Sr/82Rb, and 62Zn/62Cu generators.In the present work, in addition to 18F isotope 68Ga has been used.68Ga is the most promising as it can be produced from a generator system consisting of an inorganic or organic matrix immobilizing the parent radionuclide 68Ge.In addition to its accessibility via a generator, Gallium-68 possesses significant advantages as a positron emitter.The physical half-life of 68 minutes is consistent with the pharmacokinetics of various radiopharmaceuticals that have a low molecular weight, including but not limited to antibody fragments, peptides, aptamers, and oligonucleotides.The decay of Gallium-68 occurs through two distinct pathways, namely positron emission and electron capture, with the first type accounting for 89% of the total decay and the second one accounting for the remaining 11%.The upper limit of positron energy is recorded as 1,899 KeV, while the mean energy per disintegration is estimated to be 740 KeV.
The isotope 68Ge, which serves as the parent isotope, possesses a notably extended half-life of 271 days.This characteristic enables its regular production and transportation.Moreover, the chemical properties of Ge (IV) and Ga(III) exhibit significant differences, thereby facilitating multiple efficient separation techniques.The utilization of a generator allows the creation of a variety of cold and freeze-dried kits that can be rehydrated, labelled, and requisitioned at any given time.

System description and data acquisition
In this work, we analyzed images acquired using two distinct PET-CT scanners from two different manufacturers; Gemini TOF PET/CT (Philips Medical Systems) scanner and biograph mCT flow PET/CT scanner (Siemens Healthineers).The imaging equipment utilized was a Philips Medical Systems Gemini TOF PET/CT scanner, designated as Scanner 1.The system in question is a threedimensional time-of-flight (TOF) system.The imaging facility is equipped with a 16-slice Brilliance CT scanner manufactured by Philips Ltd, with a transaxial field of view (FOV) measuring 576 mm.The PET component of the Gemini TOF consists of 28 flat units, with each unit consisting of a 23 × 44 array of 4 × 4 × 22 mm3 lutetium-yttrium oxyorthosilicate crystals.The transverse coupling of the individual modules results in a scanner ring diameter of 90.34 cm.Lead shielding with a thickness of 2.5 cm is utilized in the form of an annulus that is fixed at both axial ends to minimize the detection of events arising from out of field radiation.The diameter of the scanner bore measures 71.7 cm, while its active transverse and axial fields of view (FOVs) are 57.6 cm and 18 cm, respectively.The process of signal readout is executed through a hexagonal configuration comprising 420 photomultiplier tubes, each with a diameter of 39 mm.Scanner 2 was Biograph mCT flow PET/CT scanner (Siemens Healthineers).It is a fast LSO scintillator with 20,280 elements with diameter of 4 mm.it is Time-of-Flight ready system.the LSO crystals has an axial field of view (FOV) of 164 mm while the CT field -of-view is 700 mm.The total system weight is 3,298 kg and the 304ing PET gantry is 46 kg lighter than the 4-ring PET gantry.It is a 3D acquisition mode and 3DOSEM reconstruction and it has a dual-monitor acquisition workplace.The detector is a multislice ultra-fast ceramic.The standard cardiac rotation time:0.6 s/0.48 s.

Image quality and SUV
Using the NEMA/International Electrotechnical Commission (IEC) Torso Phantom (see figure 1), measurements were measured (Data Spectrum).Internal diameters of the phantom's six spheres are 10, 13, 17, 22, 28, and 37 mm.The two largest spheres were filled with a water solution, whereas the four smallest large spheres were filled with a radioactive tracer.The phantom consists of a cylindrical insert measuring 50-mm in diameter, which is filled with Styrofoam beads having a density of 0.3 g/cm3(Philips Ltd) to simulate lung tissue.The assessments were executed in compliance with the RC value for 18 F was 0.81 ± 0.02, while the RC value for 68 Ga was 0.69 ± 0.02.The RC values could have important implications for the therapeutic interpretation of PET/CT scans, particularly in cases where both 18 F and 68 Ga tracers.

SUV Measurements
The measurement of the uptake of a radiotracer in a patient's body is frequently assessed through employment of the standard uptake value (SUV) of positron emission tomography (PET) imaging. 18F and 68 Ga are frequently utilized in PET imaging.In the present study, the max values of SUV of 18 F and 68 Ga were measured using Gemini TOF and Biograph mCT PET/CT systems.A subsubsection.The paragraph text follows on from the subsubsection heading but should not be in italic.   F and 68 Ga when using Philips Gemini TOF system and Siemens Biograph mCT system.Based on the data presented in the Figures, it can be observed that the maximum standardized uptake values (SUVmax) for 18 F were consistently higher than those for 68 Ga across both scanners.Specifically, the SUVmax values for 18 F ranged from 1.46 to 2.98 when using the Gemini TOF PET/CT scanner, while the corresponding range for 68 Ga was 0.12 to 2.7.Similarly, when utilizing the Biograph mCT PET/CT scanner, the SUVmax values for 18 F ranged from 1.7 to 3.04, whereas the range for 68 Ga was 0.11 to 2.9.These finds are consistent with several studies that determined the value of SUVmax of 18 F and 68 Ga such as Bhattaru et al.,2018 [13] where he compared the SUVmax values of 18 F and 68 Ga in patients with neuroendocrine tumors employing a Gemini Time-of-Flight (TOF) PET/CT scanner.The study found that the SUVmax values for 18 F were higher than those for 68 Ga in all tumor types, with statistically significant differences observed in pancreatic neuroendocrine tumors and small bowel neuroendocrine tumors.They noted that the observed dissimilarities can be attributed to variances in the pharmacokinetics of the two radiotracers.Another study by Bailly et al., (2016) [14] compared the SUVmean values of 18 F and 68 Ga in patients with neuroendocrine tumors using a Gemini Time-of-Flight (TOF) PET/CT scanner.They found that the SUVmean values for 18 F were higher than those for 68 Ga in all tumor types, with statistically significant differences observed in pancreatic neuroendocrine tumors and small bowel neuroendocrine tumors.According to our results and previous studies we conclude that the differences in those values were likely due to differences in the pharmacokinetics of the two radiotracers.

Conclusion
The study offers valuable insights into the performance features of the Gemini TF PET/CT and the Biograph mCT flow PET/CT systems with respect to 18 F and 68 Ga imaging.Additionally, the study highlights the importance of using advanced reconstruction algorithms for accurate quantification, as well as the need for careful consideration of tracer selection and interpretation of results based on the specific tracer that was used.The Recovery Coefficient (RC) value of 18 F and 68 Ga radiotracers can vary depending on the specific imaging protocol used and the type of tissue being imaged.However, in F-18 Ga-68 general, 18 F radiotracers tend to have higher RC values than 68 Ga radiotracers due to the higher energy of the 18 F positron emissions, which can result in better image resolution and less partial volume effect.several studies comparing the RC values of 18 F and 68 Ga in different types of tumours imaging found that the RC values were generally higher for 18 F particularly in small lesions and in lesions located in difficult-to-image locations such as the liver and pancreas.The maximum standardized uptake value (SUVmax) is a quantitative measure that used to assess the amount of radiotracer uptake within a specific tissue or region of the human body.The 18 F radiotracer is frequently employed in positron emission tomography (PET) imaging and is known to possess a higher maximum standardized uptake value (SUVmax) compared to 68 Ga.This is consistent with the results obtained in our current study where the study showed convergence and slightly increase in the RC and SUVmax values of 18 F as compared with 68 Ga However, it is important to note that the RC value can also be influenced by factors such as the imaging system, reconstruction algorithm, and acquisition time, among others.

Fig 6 and
Fig 6 and Fig 7 show SUVmax values of18 F and 68 Ga when using Philips Gemini TOF system and Siemens Biograph mCT system.Based on the data presented in the Figures, it can be observed that the maximum standardized uptake values (SUVmax) for 18 F were consistently higher than those for 68 Ga across both scanners.Specifically, the SUVmax values for 18 F ranged from 1.46 to 2.98 when using the Gemini TOF PET/CT scanner, while the corresponding range for 68 Ga was 0.12 to 2.7.Similarly, when utilizing the Biograph mCT PET/CT scanner, the SUVmax values for 18 F ranged from 1.7 to 3.04, whereas the range for 68 Ga was 0.11 to 2.9.These finds are consistent with several studies that determined the value of SUVmax of 18 F and 68 Ga such as Bhattaru et al.,2018[13] where he compared the SUVmax values of 18 F and 68 Ga in patients with neuroendocrine tumors employing a Gemini Time-of-Flight (TOF) PET/CT scanner.The study found that the SUVmax values for 18 F were higher than those for 68 Ga in all tumor types, with statistically significant differences observed in pancreatic neuroendocrine tumors and small bowel neuroendocrine tumors.They noted that the observed dissimilarities can be attributed to variances in the pharmacokinetics of the two radiotracers.Another study byBailly et al., (2016) [14] compared the SUVmean values of 18 F and 68 Ga in patients with neuroendocrine tumors using a Gemini Time-of-Flight (TOF) PET/CT scanner.They found that the SUVmean values for 18 F were higher than those for 68 Ga in all tumor types, with statistically significant differences observed in

Table 1 .
Table 1 shows the main physical properties of 18F and 68Ga [10].Physical properties of 18 F and 68 Ga.