Ultralow-dose CT of the petrous bone using iterative reconstruction technique, tin filter and high resolution detectors allows an adequate assessment of the petrous bone structures

Ferro, Marc; Armentia, E. Santos; Priegue, N. Silva; Basildo, C. Jurado; Villegas, C.A. Sepúlveda; Sánchez-Gracián, C. Delgado

doi:10.1016/j.rxeng.2020.07.008

Cited by 1 publication

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“…The tin filter has been shown to reduce radiation doses substantially for standalone CT examinations performed without contrast enhancement, for imaging of bone [ 7 – 9 ], lung nodules [ 10 , 11 ], abdominal imaging [ 12 ] and coronary calcium scoring [ 13 , 14 ], amongst others. The tin filter could potentially allow large dose reductions for ULDCT scans for PET AC compared with the standard ULDCT protocol, and for localisation/characterisation level scans performed in PET-CT, but the effect of the tin filter on PET quantification should be ascertained, since the tin filter increases average beam energy, thereby impacting CT HUs.…”

Section: Introductionmentioning

confidence: 99%

Ultra-low-dose CT for attenuation correction: dose savings and effect on PET quantification for protocols with and without tin filter

Bebbington,

Christensen,

Østergård

et al. 2023

EJNMMI Phys

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Background Ultra-low-dose (ULD) computed tomography (CT) scans should be used when CT is performed only for attenuation correction (AC) of positron emission tomography (PET) data. A tin filter can be used in addition to the standard aluminium bowtie filter to reduce CT radiation dose to patients. The aim was to determine how low CT doses can be, when utilised for PET AC, with and without the tin filter, whilst providing adequate PET quantification. Methods A water-filled NEMA image quality phantom was imaged in three configurations with 18F-FDG: (1) water only (0HU); (2) with cylindrical insert containing homogenous mix of sand, flour and water (SFW, approximately 475HU); (3) with cylindrical insert containing sand (approximately 1100HU). Each underwent one-bed-position (26.3 cm) PET-CT comprising 1 PET and 13 CT acquisitions. CT acquisitions with tube current modulation were performed at 120 kV/50 mAs-ref (reference standard), 100 kV/7 mAs-ref (standard ULDCT for PET AC protocol), Sn140kV (mAs range 7–50-ref) and Sn100kV (mAs range 12–400-ref). PET data were reconstructed with μ-maps provided by each CT dataset, and PET activity concentration measured in each reconstruction. Differences in CT dose length product (DLP) and PET quantification were determined relative to the reference standard. Results At each tube voltage, changes in PET quantification were greater with increasing density and reducing mAs. Compared with the reference standard, differences in PET quantification for the standard ULDCT protocol for the three phantoms were ≤ 1.7%, with the water phantom providing a DLP of 7mGy.cm. With tin filter at Sn100kV, differences in PET quantification were negligible (≤ 1.2%) for all phantoms down to 50mAs-ref, proving a DLP of 2.8mGy.cm, at 60% dose reduction compared with standard ULDCT protocol. Below 50mAs-ref, differences in PET quantification were > 2% for at least one phantom (2.3% at 25mAs-ref in SFW; 6.4% at 12mAs-ref in sand). At Sn140kV/7mAs-ref, quantification differences were ≤ 0.6% in water, giving 3.8mGy.cm DLP, but increased to > 2% at bone-equivalent densities. Conclusions CT protocols for PET AC can provide ultra-low doses with adequate PET quantification. The tin filter can allow 60–87% lower dose than the standard ULDCT protocol for PET AC, depending on tissue density and accepted change in PET quantification.

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