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. 2015 Dec;2(1):26.
doi: 10.1186/s40658-015-0132-1. Epub 2015 Oct 26.

Performance evaluation of the Biograph mCT Flow PET/CT system according to the NEMA NU2-2012 standard

Ivo Rausch  1 , Jacobo Cal-González  2 , David Dapra  3 , Hans Jürgen Gallowitsch  4 , Peter Lind  5 , Thomas Beyer  6 , Gregory Minear  7
Affiliations

Performance evaluation of the Biograph mCT Flow PET/CT system according to the NEMA NU2-2012 standard

Ivo Rausch et al. EJNMMI Phys. 2015 Dec.

Abstract

Background: The purpose of the study is to evaluate the physical performance of a Biograph mCT Flow 64-4R PET/CT system (Siemens Healthcare, Germany) and to compare clinical image quality in step-and-shoot (SS) and continuous table motion (CTM) acquisitions.

Methods: The spatial resolution, sensitivity, count rate curves, and Image Quality (IQ) parameters following the National Electrical Manufactures Association (NEMA) NU2-2012 standard were evaluated. For resolution measurements, an (18)F point source inside a glass capillary tube was used. Sensitivity measurements were based on a 70-cm-long polyethylene tube, filled with 4.5 MBq of FDG. Scatter fraction and count rates were measured using a 70-cm-long polyethylene cylinder with a diameter of 20 cm and a line source (1.04 GBq of FDG) inserted axially into the cylinder 4.5 cm off-centered. A NEMA IQ phantom containing six spheres (10- to 37-mm diameter) was used for the evaluation of the image quality. First, a single-bed scan was acquired (NEMA standard), followed by a two-bed scan (4 min each) of the IQ phantom with the image plane containing the spheres centered in the overlap region of the two bed positions. In addition, a scan of the same region in CTM mode was performed with a table speed of 0.6 mm/s. Furthermore, two patient scans were performed in CTM and SS mode. Image contrasts and patient images were compared between SS and CTM acquisitions.

Results: Full Width Half Maximum (FWHM) of the spatial resolution ranged from 4.3 to 7.8 mm (radial distance 1 to 20 cm). The measured sensitivity was 9.6 kcps/MBq, both at the center of the FOV and 10 cm off-center. The measured noise equivalent count rate (NECR) peak was 185 kcps at 29.0 kBq/ml. The scatter fraction was 33.5 %. Image contrast recovery values (sphere-to-background of 8:1) were between 42 % (10-mm sphere) to 79 % (37-mm sphere). The background variability was between 2.1 and 5.3 % (SS) and between 2.4 and 6.9 % (CTM). No significant difference in image quality was observed between SS and CTM mode.

Conclusions: 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.

Keywords: Biograph mCT Flow; Image quality; NEMA evaluation.

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Figures

Fig. 1
Fig. 1
Schematic diagram of a step-and-shoot (SS) (left) and continuous (right) table motion (CTM) acquisition protocol. Within the 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 acquire 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
Fig. 2
Fig. 2
mCT Flow. Axial sensitivity profile for the measurements with the line source in the center of the field of view and at 10-cm radial offset
Fig. 3
Fig. 3
mCT Flow. a Prompts, trues, randoms, and scatter count rates. b Fraction of trues, randoms, and scatter counts vs the total number of coincidences processed. c NECR curve for the measured range of activities. d Scatter fraction (in %) for the same range of activities
Fig. 4
Fig. 4
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
Fig. 5
Fig. 5
Central slice of the image quality phantom for sequential (a) and CTM (b) acquisition modes. The sphere-to-background ratio is 8:1. The CTM acquisition followed the sequential subsequently
Fig. 6
Fig. 6
MIP of a patient scan acquired in a CTM and b SS mode. The overall activity concentration in b is about 10 % less due to radioactive decay between the two scans. Image quality is very similar. The changes in bladder filling are caused by the time between the scans. Small differences in local uptake (e.g., larynx) are supposed to be caused by continuous physiological tracer uptake
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