Reconstructed helical CT scans: Improvement in z-axis resolution compared with overlapped and nonoverlapped conventional CT scans

C. J. Kasales, K. D. Hopper, D. N. Ariola, T. R. TenHave, J. W. Meilstrup, R. P.M. Mahraj, D. Van Hook, S. Westacott, R. J. Sefczek, J. D. Barr

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Abstract

OBJECTIVE. This in vitro study was designed to assess the z-axis resolving capabilities of reconstructed helical CT scans obtained with various imaging parameters versus those of conventional CT scans and the effect of decreasing slice index on the z-axis resolution of helical CT. MATERIALS AND METHODS. A z-axis line-pair phantom was imaged using conventional nonoverlapped CT scans, conventional CT scans that overlapped by 50%, and helical CT scans with pitches of 1.0 and 1.5. All helical images were reconstructed at comparable slice indexes (image indexes of 2.0, 1.0, and 0.5 mm for pitch = 1.0, and image indexes of 3.0, 1.5, and 0.75 mm for pitch = 1.5). Midline coronal and sagittal reconstructed images were obtained to allow standardized visualization of line pairs. The reconstructed images were reviewed separately by 10 radiologists. RESULTS. The overall z-axis resolution of reconstructed helical CT scans equaled or exceeded that of nonoverlapped conventional CT scans in all cases and equaled that of 50% overlapped conventional CT scans in 75% of cases. The 1.0-pitch helical sequences showed improved z-axis resolution with decreasing slice index. No statistically significant improvement in z-axis resolution could be determined by the observers for 1.5-pitch sequences with decreasing slice index. CONCLUSION. The use of helical CT with a pitch of 1.0 or 1.5 and an increased slice index can improve the z-axis resolution of reconstructed images when compared with nonoverlapped conventional CT and frequently equals the resolution of 50% overlapped conventional CT. This improvement in z-axis resolution should improve the appearance of reconstructed images (as used in CT angiography and three-dimensional imaging) by reducing partial volume artifacts while affording faster scanning at a reduced skin-surface radiation dose.

Original languageEnglish (US)
Pages (from-to)1281-1284
Number of pages4
JournalAmerican Journal of Roentgenology
Volume164
Issue number5
DOIs
StatePublished - Jan 1 1995

All Science Journal Classification (ASJC) codes

  • Radiology Nuclear Medicine and imaging

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    Kasales, C. J., Hopper, K. D., Ariola, D. N., TenHave, T. R., Meilstrup, J. W., Mahraj, R. P. M., Van Hook, D., Westacott, S., Sefczek, R. J., & Barr, J. D. (1995). Reconstructed helical CT scans: Improvement in z-axis resolution compared with overlapped and nonoverlapped conventional CT scans. American Journal of Roentgenology, 164(5), 1281-1284. https://doi.org/10.2214/ajr.164.5.7717248