Iterative reconstruction: Improvement of image quality for dynamic CT brain perfusion imaging

Zielsetzung:

To quantify impact of iterative reconstruction (iDose) on image noise, increase of SNR and CNR of grey and white brain matter and to ivestigate radiation dose savings by evaluation of stability of two PCT parameters (rCBV in iMTT) as descriptors of the tissue at risk and of the infarct core.

Material und Methodik:

CTP was obtained in 27 consecutive patients using a 256- slice CT (128 detector rows, flying z- focus, 8-cm detector width, 80 kV, 120 mAs, 20 measurements, 1 CT image/2.5 s). Images were reconstructed with filtered backprojection (FBP) and five different levels of IR (LD 1- LD 5). Noise, CNR (cortex vs. white matter), SNR and rCBV in iMTT were determined.

Ergebnisse:

Noise was reduced from 5.7 ± 0.1 (FBP) to 3.8 ± 0.2 (LD 5) for grey cortex and from 6.4 ± 0.0 (FBP) to 4.0 ± 0.1 (LD 5) for white matter. SNR improved from 6.7 ± 3.3 (FBP) to 10.3 ± 0.6 (LD 5) for grey cortex as well as for white matter from 4.0 ± 12.3 (FBP) to 6.5 ± 3.3 (LD 5). CNR increased from 2.2 ± 0.1 (FBP) to 3.5 ± 0.1 (LD 5) for grey matter vs. white matter. The parameter rCBV in iMTT were varying only slightly with a mean value of rCBV 4.1 ± 0.1 and a mean relation relation rCBV/nCBV 0.27 ± 0.02 for all IR- levels.

Schlussfolgerungen:

Iterative recontruction can improve SNR and CNR by noise reduction of about 33%. Therefore, iterative reconstruction may save radiation dose in brain perfusion imaging. Moreover, the use of different IR-levels of iDose (LD 1-LD 5) does not effect the CT brain perfusion parameters rCBV and MTT as two distinct PCT parameters which differ the penumbra and the infarct core in the summary maps.

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