Article Figures & Data
Figures
- Fig 1.
Graphic comparison of mean eye lens dose between 16-section and 64-section MDCT for the neuroimaging CT protocols studied.
- Fig 2.
A, Photograph of a volunteer; B, sagittal scout image with section lines of a patient in the chin tuck position during a CT brain scanning on a 64-section MDCT to remove the eyes from the radiation beam. C, Sagittal scout image with section lines for a CT brain scanning in a tilted axial mode on the 16-section MDCT for comparison.
Tables
CT Protocol* MDCT† CARE Dose‡ Set mAs Effective mAs Tube Voltage (kV) Section Collimation (mm) Beam Width (mm) Rotation Time (s) Kernel Pitch No. Brain (tilted axial mode) 16 + 400 360 120 5 12 1.0 B31f/cerebrum NA 1 – 400 NA 120 5 12 1.0 B31f/cerebrum NA 2 Brain (helical mode) 16 + 400 394 120 0.75 12 0.75 B31f/cerebrum 0.6 3 – 400 NA 120 0.75 12 0.75 B31f/cerebrum 0.6 4 64 + 400 266 120 0.6 19.2 1.0 B31f/cerebrum 0.8 5 – 400 NA 120 0.6 19.2 1.0 B31f/cerebrum 0.8 6 Paranasal sinus navigation 16 + 200 189 120 0.75 12 0.75 B70fSharp/bone 0.6 7 64 + 200 132 120 0.6 19.2 1.0 B70fSharp/bone 0.9 8 Temporal bone/orbits 16 + 400 385 120 0.6 9.6 0.75 B70fSharp/bone 0.6 9 64 + 400 355 120 0.6 19.2 15 B70fSharp/bone 0.8 10 Note:—MDCT indicates multidetector CI; NA, not applicable.
* Coverage for CT orbits is similar to that of a CT temporal bone, but a different CT kernel is used.
† 16 MDCT refers to 16-section MDCT scanner and 64 MDCT refers to 64-section MDCT scanner.
‡ CARE dose + indicates that the ATCM program is on; CARE dose − indicates that the program is off.
- Table 2:
Average eye lens dose for each imaging protocol with CTDIvol and DLP measurements*
CT Protocol MDCT CARE Dose CTDIvol (mGy) (mean ± SD) DLP (mGy.cm) (mean ± SD) Eye Lens Dose (mGy) (mean ± SD) PValue No. Brain (tilted axial mode) 16 + 63.36 ± 2.18 (60.48, 65.86) 930.50 ± 61.08 (847.00, 988.00) 15.56 ± 4.18 (10.20, 22.50) NS (.183) 1 – 67.20 ± 0 (67.20, 67.20) 985.67 ± 32.26 (941.00, 1008.00) 18.14 ± 7.59 (10.60, 36.00) 2 Brain (helical mode) 16 + 83.44 ± 0.42 (83.15, 84.02) 1421.33 ± 94.54 (1301.00, 1512.00) 82.16 ± 13.43 (56.50, 97.90) NS (.096) 3 – 84.30 ± 0 (84.30, 84.30) 1449.67 ± 94.43 (1319, 1517) 88.83 ± 13.47 (65.30, 102.60) 4 64 + 36.77 ± 1.76 (35.31, 39.34) 601.33 ± 47.48 (559, 669) 47.18 ± 5.99 (36.2, 60.0) <.000 5 – 53.33 ± 0.06 (53.30, 53.46) 870.83 ± 32.00 (831, 909) 63.90 ± 7.74 (49.10, 75.90) 6 Paranasal sinus navigation 16 + 40.57 ± 0.66 (39.42, 41.14) 563.67 ± 28.24 (524, 595) 45.90 ± 2.65 (40.3, 50.00) <.000 7 64 + 20.69 ± 0.77 (19.96, 21.82) 301.83 ± 7.11 (289, 310) 28.96 ± 3.35 (22.80, 35.30) 8 Temporal bone/orbits 16 + 102.86 ± 7.08 (92.71, 109.31) 483.33 ± 48.84 (424, 541) 98.58 ± 9.03 (83.00, 111.7) <.000 9 64 + 46.71 ± 2.07 (43.88, 48.59) 298.50 ± 20.97 (270, 318) 53.57 ± 10.07 (39.10, 70.50) 10 Note:—NS indicates not significant; CTDIvol, volume CT dose index; DLP, dose-length product.
* The CTDIvol, DLP, and eye lens doses are tabulated as mean ± SD with the minimum and maximum values in parentheses. Comparison was made between protocols using the paired Student t test, and statistical significance was defined at P < .05.
- Table 3:
Comparison of eye lens dose savings on CT brain protocols using ATCM between titled axial-versus-helical modes and 16-section-versus-64-section MDCT
CT Brain Protocol* MDCT CARE Dose Mean Eye Lens Dose (mGy) Dose Savings (%) (P value) Protocol No. Tilted axial 16 + 15.56 81.1 (.000) 1 Helical 82.16 3 Tilted axial 16 + 15.56 67.0 (.000) 1 Helical 64 47.18 5 Helical 16 + 82.16 42.6 (.000) 3 64 47.18 5 Note:—ATCM indicates automatic tube current modulation.
* Comparison was made between protocols using the paired Student t test, and statistical significance was defined at P < .05.
CT Protocol MDCT CARE Dose Cadaveric Cases Clinical Cases CTDIvol (mGy) (mean ± SD) DLP (mGy.cm) (mean ± SD) CTDIvol (mGy) (mean ± SD) DLP (mGy.cm) (mean ± SD) Brain (tilted axial mode) 16 + 63.36 ± 2.18 930.50 ± 61.08 59.56 ± 2.25 857.00 ± 24.49 Brain (helical mode) 64 + 36.77 ± 1.76 601.33 ± 47.48 39.43 ± 1.30 711.67 ± 35.43 Paranasal sinus navigation 16 + 40.57 ± 0.66 563.67 ± 28.24 40.19 ± 1.01 587.17 ± 60.49 64 + 20.69 ± 0.77 301.83 ± 7.11 23.37 ± 1.19 334.33 ± 28.79 Temporal bone/orbits 16 + 102.86 ± 7.08 483.33 ± 48.84 104.45 ± 6.78 648.17 ± 132.09 64 + 46.71 ± 2.07 298.50 ± 20.97 58.34 ± 7.08 487.00 ± 84.38 * Clinical scanning is routinely performed with ATCM. The CTDIvol and DLP values for clinical brain scans acquired in the helical mode on the 16-section MDCT are not available for comparison. This is because the protocol is only used in the rare clinical situation when the tilted axial mode cannot be executed (eg, patients in a cervical collar).
