The purpose of the study is to evaluate the physical performance of a Biograph mCT Flow R PET/CT system (Siemens Healthcare, Germany) and to. to fundamentally change how PET imaging is performed. Powered by Siemens’ revolutionary FlowMotion™ technology,. Biograph mCT Flow™ is the world’s first. Biograph mCT Flow with FlowMotion™ technology combines our standard- setting PET/CT with a unique system design that enables continuous motion of.
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For resolution measurements, an 18 F point source inside a glass capillary tube was used. Sensitivity measurements were based on a biogfaph polyethylene tube, filled with 4. In addition, a scan of the same region in CTM mode was performed with a table speed of 0. The measured sensitivity was 9. The scatter fraction was Image contrast recovery values sphere-to-background of 8: The background variability was between 2.
The spatial resolution, sensitivity, scatter fraction, and count rates were in concordance with the published values for the predecessor system, the Biograph mCT. Contrast recovery values as well as image quality obtained in SS and CTM acquisition modes were similar.
The TOF measurement of two coincidence photons allows the localization of the positron annihilation point with a spatial accuracy that depends on the system timing resolution.
This information can be used to significantly improve the image signal-to-noise ratio SNR of the reconstructed PET images, thus, allowing for better image quality and shorter acquisition times [ 89 ]. Traditionally, whole-body PET examinations are performed in step-and-shoot SS mode, introducing the patient table motion between consecutive acquisitions of adjacent bed positions [ 1011 ].
For this acquisition protocol, planning and scanning are restricted by the fixed size of the detector array. Using this acquisition mode, the patient is moved through the gantry while PET emission data is continuously acquired. This technique was proposed by Dahlbom and colleges in [ 13 ] and integrated in a first PET-only system in [ 14 ].
The advantage of the continuous bed motion is the increase of uniformity in the sensitivity profile across the axial FOV, due to the fact that the density of lines of response LOR does not depend of their axial position as in the case of SS acquisitions [ 13 ]. Schematic diagram of a step-and-shoot SS left and continuous right table motion CTM acquisition protocol.
Within bioraph SS protocol, the table is in a fixed position during an acquisition of data in the FOV and subsequently moves to the next position to bigraph data of an axial range greater than the axial FOV of the system.
In CTM, the table is moved continuously through the axial FOV of the scanner to acquire date of an extended scan range. The evaluation of positron emission tomographs requires reproducible and reliable methods to allow the comparison of different systems using accepted measurement standards.
Finally, the results of these measurements were compared with published values from its predecessor, the Biograph mCT system [ 6 ]. This configuration provides an axial field-of-view FOV of The CTM FlowMotion technology requires a new design of the patient table and the acquisition electronics. The patient handling system PHS contains a horizontal magnetic drive system that enables a continuous table motion with a positioning accuracy of less than 0.
Table speeds range from 0. Similar to CT acquisitions, the FlowMotion acquisition system tracks the bed position in real time and stores this information in the listmode data file as a new tag for each coincidence event [ 20 ].
The extra bed position information is then employed during the data processing, thus, assuring that the final reconstructed images contain the correct position information. The acquisition electronics is based on solid-state components capable of continuously recording and storing detector addresses. All measurements were performed at the site of the clinical installation of the system between August and December At the start of the first measurement, the activity of the point source was 0.
Data were acquired at three transaxial locations xy: TOF information was not used in this measurement. No biigraph and scatter correction and no post-smoothing filter were applied.
The measurements were performed at the center of the FOV and at cm radial offset. Online random subtraction was applied from a delayed coincidence window. The corrected true coincidence cmt rate was recorded as a function of sleeve thickness and extrapolated to a zero thickness sleeve. The system sensitivity was then computed as the ratio between the true count rate with no absorption and the starting activity.
The line source was filled with an initial activity of 1. Online random subtraction was applied from the delayed coincidence window to account also for the intrinsic LSO radioactivity [ 23 ].
The scatter fraction and NECR were bkograph as described in the NEMA NU standard [ 19 ] acquired using software tools provided by biogeaph manufacturer and evaluated using in-house software. System true event rate, random event rate, scatter event rate, NECR, and the scatter fraction are reported.
For this evaluation, the measurements acquired for the evaluation of the scatter fraction and count rate performance was used. Evaluation was done using in-house software.
The axial end slices first and last slice were excluded from the analysis. Maximum modulus count rate error at peak NECR as well as maximum and minimum error for all activity concentrations are reported. The four smallest spheres were filled with a target-to-background ratio TBR of 8: The remaining two largest spheres were filled with non-radioactive water.
The phantom was positioned with all spheres aligned within the same transaxial image plane in the center of the FOV. The line source for the scatter phantom was filled with a solution of 18 F-FDG and water.
All data were corrected for random coincidences, normalization, dead time losses, scatter, and attenuation. Data were reconstructed with mt ordered-subset expectation maximization OSEM [ 25 ] 3D iterative algorithm, using 2 iterations i and 24 subsets sand additionally with 2 iterations and 21 subsets applying PSF correction and TOF.
The average and range percent contrast obtained for hot and cold spheres, the average and range standard deviation of the background counts, and the mean residual error in scatter and attenuation corrections were evaluated.
A second scan of the same region in CTM mode was acquired at a table speed of 0. Furthermore, biogrzph accuracy of scatter and attenuation corrections in both acquisition modes was evaluated. The contrast values, background variability, and the accuracy of attenuation and scatter correction for the lung insert were evaluated with an in-house developed plug-in for ImageJ U.
Biograph mCT – Siemens Healthineers Global
The CTM scans were acquired with a table speed of 1. These settings were selected to cover the same axial FOV in the same time as performed with the IQ phantom measurements.
Whole-body images were compared visually by two experienced imaging specialists one nuclear medicine physician and one imaging physicist. Mean standardized uptake values SUVs mean and coefficient of variations CVs were calculated for spherical volumes of interest VOI with 3-cm diameter placed in the liver and the bladder. No noticeable differences were found between the two systems.
The mCT Flow system had a sensitivity of 9. The axial sensitivity profiles with the line source placed at the center of the FOV and cm radial offset are shown in Fig. Axial sensitivity profile for the measurements with the line source in the center of the field of view and at cm radial offset. The scatter fraction was calculated to be No noticeable difference between the two systems was observed.
Plots of the trues, randoms, and scatter event rates as well as the NECR and the scatter fraction curves as a function of activity are shown in Fig. The relative count rate error at the activity concentration of the NECR peak The maximum and minimum errors for all activity concentrations are depicted in Fig. Maximum solid line and minimum dashed line relative count rate error for the different activity distributions.
The first and the last slice of the acquisitions were excluded from this evaluation. The calculated activities at the start of the second scan were 5. Image quality results for 4: The reconstructions of the transaxial sections through the center of the spheres within the image quality phantom for SS and CTM mode are shown in Fig.
The sphere-to-background ratio is 4: Central slice of the image quality phantom for sequential a and CTM b acquisition modes.
The sphere-to-background ratio is 8: The CTM acquisition followed the sequential subsequently. No visual difference in overall PET image quality was observed by two experienced imaging experts. Nonetheless, increased noise was observed in the images acquired in SS mode Fig. Biograpn quality is very similar.
The changes in bladder filling are caused by the time between the scans.
Biograph mCT Flow
Small differences in local uptake e. SUV mean values and CVs of reference regions in the biograpn patient scans. Our data indicate a similar performance of the PET components of the mCT Flow and its predecessor system, the mCT [ 6 ] with the residual differences being discussed below.
The most significant difference between both standards is the change of the positions of the point source for spatial resolution measurements.
Furthermore, the axial placement of the off-center axial point sources was changed from one fourth of the axial FOV from the center to three eighth of the biograpph FOV from the center, respectively.
Of note, the standard permits for a range bigraph image reconstruction methods. Thus, users may opt for applying PSF and other geometric corrections to the data, which inevitable makes inter-system comparisons more difficult. For the measurements for the sensitivity, the count rate performance, and the associated relative count rate error, a provision was made in NEMA NU for elevating the phantoms, if the vertical range of boograph patient table is insufficient for the required placement of the phantoms.
Biograph mCT Flow – Siemens Healthineers USA
Furthermore, the filling tolerance was expanded and a method for correcting the measured activity concentration for axially extended in-tube activity was introduced.
Biobraph, here, the patient handling system had a sufficient vertical table range and the line sources were filled to meet exactly the mm in-tube filling, and, therefore, these changes were not applicable to our measurements.
The count rate error evaluation was also slightly modified in the standard. The expected value of the true count rate is gained by a fit through all data below the peak NECR standard as opposed to the extrapolated values from the last three acquisitions standard. While the difference in error may be small, the exclusion of the end slices as permitted in the NEMA NU protocol should be followed anyway, as these end slices boograph suffer from high noise levels due to the low sensitivity of the scanner at the end of the axial FOV Fig.
Despite the modifications from the to the standard, the results for the system sensitivity, the count rates, NECR, scatter fraction, corrections for count losses and random measurements as well as the count rate error are in biohraph with published values for the mCT system [ 6 ] following the NEMA NU standard. Regarding the IQ test, the only difference between the and standard is a reduction of emission scan time by a factor of 2.
Nevertheless, contrast recoveries for both reconstructions were substantially lower than the values published for the mCT system [ 6 ].
This difference warrants further discussion. A possible explanation could be the differences in reconstruction algorithms and post-filtering used in [ 6 ] and here.