Photon-counting CT of elbow joint fractures: image quality in a simulated post-trauma setting with off-center positioning

European Radiology Experimental

Table 1 Acquisition and reconstruction parameters

	Photon-counting detector CT	Energy-integrating detector CT
Acquisition parameters
Scanner^a	NAEOTOM Alpha	SOMATOM Force
Collimation	24 × 0.2	19.2 × 0.6
Scan mode	UHR	UHR^b
Tube potential (kVp)	120	120
Tube-current-time-product (mAs)	2 mGy (25 mAs) 6 mGy (75 mAs) 12 mGy (149 mAs)	2 mGy (35 mAs) 6 mGy (104 mAs) 12 mGy (207 mAs)
Rotation time (s/rotation)	1	1
Pitch factor	0.8	0.8
Reconstruction parameters
Reconstruction type (image type)	QIR (T3D)	ADMIRE (UHR, 120 kV)
Iterative reconstruction strength (number of steps)	3	3
Slice thickness/increment (mm)	0.2/0.1	0.4/0.2
Field of view (mm)	100 × 100	100 × 100
Matrix size (no. of pixels)	512 × 512	512 × 512
Maximum image resolution^c (rho max; linepairs/cm)	25.6	25.6
Kernel parameters (rho10; linepairs/cm)	Br76 (21.01) Br89 (30.01)	Ur77 (21.99) Ur89 (30.01)

ADMIRE Advanced model-based iterative reconstruction, Br Body regular, CT Computed tomography, QIR Quantum iterative reconstruction, T3D Manufacturer’s name for the images created using photon energies from the low-energy threshold (20 keV) to the maximum possible energy (120 keV), UHR Ultra-high resolution, Ur Ultra-high-resolution regular (comb filter)
^aAll scanners manufactured by Siemens Healthineers GmbH, Forchheim, Germany
^bWith a highly attenuating, post-patient comb filter at the expense of radiation dose efficiency
^cMaximum spatial frequency (rho max) that can be displayed in reconstructed images, determined by the field of view and the matrix size, approximated by the following equation: rho max = 1/(2 × FOV [cm]/matrix size [pixels]) based on the Nyquist theorem [14]