EFOMP's protocol quality controls in PET/CT and PET/MR.

This article presents the protocol on Quality Controls in PET/CT and PET/MRI published online in May 2022 by the European Federation of Organisations for Medical Physics (EFOMP), which was developed by the Working group for PET/CT and PET/MRI Quality Control (QC) protocol. The main objective of this protocol was to comprehensively provide simple and practical procedures that may be integrated into clinical practice to identify changes in the PET/CT/MRI system's performance and avoid short- and long-term quality deterioration. The protocol describes the quality control procedures on radionuclide calibrators, weighing scales, PET, CT and MRI systems using selected and measurable parameters that are directly linked to clinical images quality. It helps to detect problems before they can impact clinical studies in terms of safety, image quality, quantification accuracy and patient radiation dose. CT and MRI QCs are described only in the context of their use for PET (attenuation correction and anatomical localization) imaging. Detailed step-by-step instructions have been provided, limiting any misinterpretations or interpersonal variations as much as possible. This paper presents the main characteristics of the protocol illustrated together with a brief summary of the content of each chapter. A regular QC based on the proposed protocol would guarantee that PET/CT and PET/MRI systems operate under optimal conditions, resulting in the best performance for routine clinical tasks.

Quality control in PET/CT and PET/MRI: Results of a survey amongst European countries.

PURPOSE: An EFOMP Working Group (WG) was created in 2020 to establish recommendations for PET/CT/MRI Quality Control (QC). The WG's intention was to create a document containing a set of measurements suitable for routine practice. In order to map the current situation in PET facilities, the WG prepared a survey addressed to European Medical Physics Experts (MPE). METHODS: The survey was conducted using an electronic questionnaire with 10 sections, for a total of 43 multiple choice or open questions. Data regarding general information, model of installed scanners, contract of maintenance and phantoms available were collected. The focal part of the questionnaire concerned the QC protocol adopted and accreditation programs. RESULTS: 123 answers from 24 countries were collected. 90.2% of the respondents are affiliated as staff MPEs; 45% have non-digital TOF PET/CT scanners with a contract of maintenance (97.6%). In 98.4% and 86.8% of responding centres a sealed source for daily QC and the NEMA Image Quality Phantom were present. 94.3% of respondents perform daily QC according to manufacturer recommendations, while NEMA Tests are not performed routinely (51.2%). 56.1% of the respondents have scanners accredited by a national or international organization. 56% of the centres perform annual CT tests, while more than 90% do not perform any MRI QCs. CONCLUSIONS: The results of the survey show that there is a lack of harmonization in the PET QC procedures across Europe. The information obtained will guide the WG in proposing a guideline containing a set of measurements suitable for the clinical routine.

Development and performance assessment of an advanced Lucas-Kanade algorithm for dose mapping of cervical cancer external radiotherapy and brachytherapy plans.

PURPOSE: The aim of this study was to verify the possibility of summing the dose distributions of combined radiotherapeutic treatment of cervical cancer using the extended Lucas-Kanade algorithm for deformable image registration. MATERIALS AND METHODS: First, a deformable registration of planning computed tomography images for the external radiotherapy and brachytherapy treatment of 10 patients with different parameter settings of the Lucas-Kanade algorithm was performed. By evaluating the registered data using landmarks distance, root mean square error of Hounsfield units and 2D gamma analysis, the optimal parameter values were found. Next, with another group of 10 patients, the accuracy of the dose mapping of the optimized Lucas-Kanade algorithm was assessed and compared with Horn-Schunck and modified Demons algorithms using dose differences at landmarks. RESULTS: The best results of the Lucas-Kanade deformable registration were achieved for two pyramid levels in combination with a window size of 3 voxels. With this registration setting, the average landmarks distance was 2.35 mm, the RMSE was the smallest and the average gamma score reached a value of 86.7%. The mean dose difference at the landmarks after mapping the external radiotherapy and brachytherapy dose distributions was 1.33 Gy. A statistically significant difference was observed on comparing the Lucas-Kanade method with the Horn-Schunck and Demons algorithms, where after the deformable registration, the average difference in dose was 1.60 Gy (P-value: 0.0055) and 1.69 Gy (P-value: 0.0012), respectively. CONCLUSION: Lucas-Kanade deformable registration can lead to a more accurate model of dose accumulation and provide a more realistic idea of the dose distribution.

Optimal reconstruction matrix and PET image filtration for point-spread function and time-of-flight reconstruction - A phantom study.

INTRODUCTION: The aim of this study was to determine the optimal image matrix and half-width of the Gaussian filter after iterative reconstruction of the PET image with point-spread function (PSF) and time-of-flight (TOF) correction, based on measuring the recovery coefficient (RC) curves. The measured RC curves were compared to those from an older system which does not use PSF and TOF corrections. MATERIALS AND METHODS: The measurements were carried out on a NEMA IEC Body Phantom. We measured the RC curves based on SUVmax and SUVA50 in source spheres with different diameters. The change in noise level for different reconstruction parameter settings and the relation between RC curves and the administered activity were also evaluated. RESULTS: With an increasing size of image matrix and reduction in the half-width of the post-reconstruction Gaussian filter, there was a significant increase in image noise and overestimation of the SUV. The local increase in SUV, observed for certain filtrations and objects with a diameter below 13mm, was caused by PSF correction. The decrease in administered activity, while maintaining the same conditions of acquisition and reconstruction, also led to overestimation of readings of the SUV and additionally to deterioration in reproducibility. CONCLUSION: This study proposes a suitable size for the image matrix and filtering for displaying PET and SUV measurements. The benefits were demonstrated as improved image parameters for the newer instrument, these even being found using relatively strong filtration of the reconstructed images.

Analysis of planar acintigraphic images using the Li-Ma technique.

A statistics-based approach to comparison of planar scintigraphic images is introduced to provide additional information to subtraction method. The proposed procedure leads to parametric images with better noise properties allowing subsequent statistical analysis. An example of an application of the technique is given using parathyroid scintigrams. The presented technique is not intended to replace the image subtraction method but offers a tool that may help during a diagnosis-making process.

Bone SPECT image reconstruction using deconvolution and wavelet transformation: development, performance assessment and comparison in phantom and patient study with standard OSEM and resolution recovery algorithm.

PURPOSE: The aim of this work was to introduce a new algorithm for image reconstruction in bone SPECT and to compare its performances with a commercially available standard OSEM and resolution recovery (RR) reconstruction. MATERIALS AND METHODS: The algorithm was built applying the Lucy-Richardson deconvolution adn logarithmic image processing to the projections. A modification of the coefficients of wavelet decomposition was used to suppress the noise. The comparison with vendor software was performed both in a phantom study, using Signal-to-Noise ratio (SNR), Signal-to-Background ratio (SBR), spatial resolution and in clinical studies, by visual assessment of changes in contrast, spatial resolution and lesion detectability. RESULTS: A change in the SNR (from -4 to 40%), an increase in the SBR (from 19 to 40%), a minor improvement in spatial resolution and a similar noise level were observed in the phantom study in comparison to the standard OSEM. A decrease in the SNR, a worse spatial resolution, but only a 3 to 13 % lower SBR were achieved in comparison with the vendor supplied RR algorithm. The proposed algorithm creates patient images with better contrast and lesion detectability compared to clinically used OSEM. Compared to RR, more than half of obtained images showed better contrast and nearly half of them have better lesion detectability. CONCLUSION: The proposed algorithm compares favorably with the standard OSEM. Although less favorable, the comparison with RR and noise suppression algorithms, suggests that it can be used with only a slight decrease in the SBR.

Tc-99m exametazime (HMPAO)-labeled leukocyte scintigraphy in premature infants: detection and localization of necrotic enterocolitis and osteomyelitis.

Two cases of successful detection of inflammatory foci using Tc-99m exametazime (HMPAO)-labeled leukocyte scintigraphy in premature infants were reported. Necrotizing enterocolitis was detected in a child with a body weight of 1.6 kg. Scintigraphy confirmed a neonatal osteomyelitis in the distal part of the leg of another patient weighing 2.2 kg. These 2 cases indicate that it is feasible to perform Tc-99m HMPAO-labeled leukocyte scintigraphy even if the blood sample volume is lower than the minimal volumes required by the guidelines for pediatric patients.

Comparison of different techniques for stereotactic positron emission tomography imaging.

BACKGROUND AND PURPOSE: The aim of this study was to evaluate three different techniques used for stereotactic positron emission tomography (PET) image definition: (1) PET imaging with external stereotactic radioactive markers, (2) PET imaging without external stereotactic markers and subsequent coregistration with stereotactically defined imaging modality such as computed tomography (CT) or magnetic resonance imaging (MRI), (3) PET/CT imaging with utilization of external nonradioactive markers. MATERIALS AND METHODS: Special head phantom that could be fixed in the Leksell stereotactic frame was used. The phantom was filled with fluorodeoxyglucose ((18)F-FDG) in water solution at an activity concentration of 17.5 kBq/ml simulating counts from standard brain. A spherically shaped glass test vessel (inner diameter 46 mm and wall thickness 3 mm) positioned in the head phantom was filled with FDG water solution at an activity concentration of 52.5 kBq/ml corresponding to pathologic lesion during PET imaging. Leksell stereotactic MRI indicator box was filled with FDG water solution at an activity concentration of 3.1 MBq/ml. The phantom was then stereotactically investigated on PET, PET/CT, CT and MRI. Deviations between stereotactic X, Y, Z PET coordinates of the center of the spherical vessel (simulating pathological lesion) were determined in the treatment planning system according to reference image and represented inaccuracy in stereotactic PET image definition for each of three tested methods of stereotactic PET definition. RESULTS: Total spatial inaccuracy for stereotactic PET image definition based on radioactive fiducials was 1.7 and 0.7 mm for 3.4- and 2.0-mm PET slices, respectively. Total spatial PET image definition inaccuracy based on PET/CT imaging and stereotactic definition using nonradioactive CT fiducials was 0.7 mm. Total spatial PET image definition inaccuracy based on coregistration was 0.5 and 0.9 mm for coregistration with MRI and CT, respectively. CONCLUSION: All three evaluated stereotactic PET image definition techniques indicated very good accuracy in this phantom study entirely accepted by clinical requirements for functional imaging. The most convenient stereotactic PET image definition technique seemed to be PET image coregistration either on CT or MRI. In this situation, PET imaging can be done independently on frame application (for example few days before stereotactic frame application or even in a different centre) and then coregistered with stereotactically performed CT or MRI during the stereotactic procedure. However, detailed patient study has to be performed to test image coregistration inaccuracy on real clinical data.