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Optimization of Multiplanar Reformations from Isotropic Data Sets Acquired with 16–Detector Row Helical CT Scanner¹

¹ From the Department of Radiology, Duke University Medical Center, Box 3808, Durham, NC 27710. Received March 10, 2005; revision requested April 29; revision received June 22; accepted June 27; final version accepted July 8. Address correspondence to T.A.J. (e-mail: jaffe002{at}mc.duke.edu).

View larger version (187K): [in a new window]   Figure 1a: (a) High-contrast phantom used to evaluate quality of z-axis reformations by using MTFs. High-contrast inserts are placed at 90° to each other. (b) Representative transverse CT scan of high-contrast phantom acquired at 140 kVp.

View larger version (161K): [in a new window]   Figure 1b: (a) High-contrast phantom used to evaluate quality of z-axis reformations by using MTFs. High-contrast inserts are placed at 90° to each other. (b) Representative transverse CT scan of high-contrast phantom acquired at 140 kVp.

View larger version (114K): [in a new window]   Figure 2: Catphan phantom. This phantom contains separate compartments that are used for evaluation of CNR.

View larger version (109K): [in a new window]   Figure 3: Transverse and z-axis reformations of CT data acquired in high contrast phantom. The transverse scan at the top serves as the reference. The use of protocols A and B yielded diminished resolution relative to that yielded by standard transverse scanning and protocols C and D. Note the blur in the edges of all the bar patterns and the reduced gray-scale differentiation in the second-to-last pattern (arrow).

View larger version (40K): [in a new window]   Figure 4a: MTFs for the four CT protocols used to image the high-contrast phantom. (a) Protocol A (8 x 1.25 mm, 16.75 mm per rotation, pitch of 1.675). (b) Protocol B (16 x 1.25 mm, 27.50 mm per rotation, pitch of 1.375). (c) Protocol C (16 x 0.625 mm, 17.50 mm per rotation, pitch of 1.750, reconstruction thickness of 0.625 mm at 0.5-mm intervals). (d) Protocol D (16 x 0.625 mm at 17.50 mm per rotation, pitch of 1.750, reconstruction thickness of 0.625 mm at 0.625-mm intervals). Note the loss of modulation depth (the clear distinction between white and black) for protocols A and B at the higher numbers of line pairs per centimeter. The 16 x 0.625-mm protocols have comparable modulation profiles.

View larger version (39K): [in a new window]   Figure 4b: MTFs for the four CT protocols used to image the high-contrast phantom. (a) Protocol A (8 x 1.25 mm, 16.75 mm per rotation, pitch of 1.675). (b) Protocol B (16 x 1.25 mm, 27.50 mm per rotation, pitch of 1.375). (c) Protocol C (16 x 0.625 mm, 17.50 mm per rotation, pitch of 1.750, reconstruction thickness of 0.625 mm at 0.5-mm intervals). (d) Protocol D (16 x 0.625 mm at 17.50 mm per rotation, pitch of 1.750, reconstruction thickness of 0.625 mm at 0.625-mm intervals). Note the loss of modulation depth (the clear distinction between white and black) for protocols A and B at the higher numbers of line pairs per centimeter. The 16 x 0.625-mm protocols have comparable modulation profiles.

View larger version (44K): [in a new window]   Figure 4c: MTFs for the four CT protocols used to image the high-contrast phantom. (a) Protocol A (8 x 1.25 mm, 16.75 mm per rotation, pitch of 1.675). (b) Protocol B (16 x 1.25 mm, 27.50 mm per rotation, pitch of 1.375). (c) Protocol C (16 x 0.625 mm, 17.50 mm per rotation, pitch of 1.750, reconstruction thickness of 0.625 mm at 0.5-mm intervals). (d) Protocol D (16 x 0.625 mm at 17.50 mm per rotation, pitch of 1.750, reconstruction thickness of 0.625 mm at 0.625-mm intervals). Note the loss of modulation depth (the clear distinction between white and black) for protocols A and B at the higher numbers of line pairs per centimeter. The 16 x 0.625-mm protocols have comparable modulation profiles.

View larger version (48K): [in a new window]   Figure 4d: MTFs for the four CT protocols used to image the high-contrast phantom. (a) Protocol A (8 x 1.25 mm, 16.75 mm per rotation, pitch of 1.675). (b) Protocol B (16 x 1.25 mm, 27.50 mm per rotation, pitch of 1.375). (c) Protocol C (16 x 0.625 mm, 17.50 mm per rotation, pitch of 1.750, reconstruction thickness of 0.625 mm at 0.5-mm intervals). (d) Protocol D (16 x 0.625 mm at 17.50 mm per rotation, pitch of 1.750, reconstruction thickness of 0.625 mm at 0.625-mm intervals). Note the loss of modulation depth (the clear distinction between white and black) for protocols A and B at the higher numbers of line pairs per centimeter. The 16 x 0.625-mm protocols have comparable modulation profiles.

View larger version (24K): [in a new window]   Figure 5: Bar graph shows mean preference ratings for coronal images from isotropic data sets reformatted at 1-, 2-, 3-, 4-, and 5-mm thicknesses (horizontal axis). Three different readers rated the images according to diagnostic preference from 1 (best) to 5 (worst).

View larger version (209K): [in a new window]   Figure 6a: Coronal reformations of CT data acquired with 16 x 0.625 mm, 17.50 mm per rotation, pitch of 1.750, and 140 kVp (protocol D) in 52-year-old man. Note the loss of detail in the small lymph node (arrow) as section thickness increases. (a) 1-mm section thickness. Readers believed that this image was too noisy. (b) 2-mm section thickness. (c) 3-mm section thickness. (d) 4-mm section thickness. (e) 5-mm section thickness. Readers believed that d and e were too smooth.

View larger version (202K): [in a new window]   Figure 6b: Coronal reformations of CT data acquired with 16 x 0.625 mm, 17.50 mm per rotation, pitch of 1.750, and 140 kVp (protocol D) in 52-year-old man. Note the loss of detail in the small lymph node (arrow) as section thickness increases. (a) 1-mm section thickness. Readers believed that this image was too noisy. (b) 2-mm section thickness. (c) 3-mm section thickness. (d) 4-mm section thickness. (e) 5-mm section thickness. Readers believed that d and e were too smooth.

View larger version (196K): [in a new window]   Figure 6c: Coronal reformations of CT data acquired with 16 x 0.625 mm, 17.50 mm per rotation, pitch of 1.750, and 140 kVp (protocol D) in 52-year-old man. Note the loss of detail in the small lymph node (arrow) as section thickness increases. (a) 1-mm section thickness. Readers believed that this image was too noisy. (b) 2-mm section thickness. (c) 3-mm section thickness. (d) 4-mm section thickness. (e) 5-mm section thickness. Readers believed that d and e were too smooth.

View larger version (192K): [in a new window]   Figure 6d: Coronal reformations of CT data acquired with 16 x 0.625 mm, 17.50 mm per rotation, pitch of 1.750, and 140 kVp (protocol D) in 52-year-old man. Note the loss of detail in the small lymph node (arrow) as section thickness increases. (a) 1-mm section thickness. Readers believed that this image was too noisy. (b) 2-mm section thickness. (c) 3-mm section thickness. (d) 4-mm section thickness. (e) 5-mm section thickness. Readers believed that d and e were too smooth.

View larger version (189K): [in a new window]   Figure 6e: Coronal reformations of CT data acquired with 16 x 0.625 mm, 17.50 mm per rotation, pitch of 1.750, and 140 kVp (protocol D) in 52-year-old man. Note the loss of detail in the small lymph node (arrow) as section thickness increases. (a) 1-mm section thickness. Readers believed that this image was too noisy. (b) 2-mm section thickness. (c) 3-mm section thickness. (d) 4-mm section thickness. (e) 5-mm section thickness. Readers believed that d and e were too smooth.