Performance of Ultra-High-Resolution Computed Tomography in Super High–Resolution Mode at the Routine Radiation Dose: Phantom Study

Abstract

ObjectiveUsing a chest phantom, we compared the image quality of ultra-high-resolution computed tomography (U-HRCT) images acquired in super high–resolution (SHR) and normal resolution (NR) mode and at the routine radiation dose. The detector size was 0.25 and 0.5 mm, respectively.MethodsA chest phantom was scanned on a U-HRCT scanner. The scan parameters were tube voltage 120 kV and volume CT dose index 13.0 mGy, the routine radiation dose for conventional scans. The rotation time was 0.5 s/rot, the number of matrices was 512 in NR and 1024 in SHR mode. For physical evaluation, the modulation transfer function was measured on the spherical simulated nodule, and the noise power spectrum on the cylindrical water phantom. A CT value profile curve was created using an in-house simulated bronchial phantom. For visual evaluation, 3 radiologists and 3 radiology technologists evaluated overall image quality using a 4-grade scale (grade 1, poor; and grade 4, excellent).ResultsThe 10% of modulation transfer function was 13.5 lp/cm in NR and 14.9 lp/cm in SHR mode (P<0.01). ƒpeak was 5.6 lp/cm in NR and 8.8 lp/cm in SHR mode (P<0.01), and the peak of noise power spectrum shifted. On the profile curves, the CT value at the edge changed in NR but not in SHR mode. The overall image quality was grade 3.0 ± 0.7 in SHR and grade 2.0 ± 0.7 in NR mode (P<0.01).ConclusionsThe image quality of SHR mode with U-HRCT was superior to that of NR mode at the routine radiation dose.

Analysis of the precision of modulation transfer function measurements with a circular edge: influence of object circularity

“…As shown in Eq. (2), the degree of blurring depending on changes in circularity is an unsharpness coefficient independent of the true MTF, but for a high-resolution image 30 and using a high spatial frequency enhancement type algorithm, 18 we believe that the effect of distortion appears more prominently, owing to the noise or structures enhanced by imaging process, even if the imaging conditions are the same. Thus, although there are some research limitations, the knowledge gap regarding the influence of changes in the circularity of circular edges on MTF measurements addressed by this study should contribute to the appropriate interpretation of evaluation results and quantitative understanding of measurement errors when obtaining the image quality characteristics of various imaging modalities using the circular edge technique.…”