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Use of an Automatic Exposure Control Mechanism for Dose Optimization in Multi–Detector Row CT Examinations: Clinical Evaluation¹

¹ From the Department of Radiology, Heilig Hart Hospital, Kolveniersvest 20, B-2500 Lier, Belgium. Received February 12, 2004; revision requested September 14; revision received September 29; accepted November 4. Address correspondence to T.H.M. (e-mail: tom.mulkens{at}hhzhlier.be).

View larger version (173K): [in a new window]   Figure 1a. Images obtained in a 67-year-old woman (height, 1.56 m; weight, 48 kg; BMI, 19.72). Multi–detector row CT thoracic examination was performed with angular and z-axis modulation for evaluation of a mass, which was seen on a standard radiograph. Mean effective tube current of 48 mAs was used, which means there was approximately 33% reduction in comparison with the reference tube current of 70 mAs. Calculated effective dose for the whole examination was 2.75 mSv. (a) Topogram shows mass (white arrows) on the right side of the thorax. (b) A 5-mm transverse CT image obtained with the lung window setting shows tumor mass (arrow) in the superior segment of the right lower lobe.

View larger version (160K): [in a new window]   Figure 1b. Images obtained in a 67-year-old woman (height, 1.56 m; weight, 48 kg; BMI, 19.72). Multi–detector row CT thoracic examination was performed with angular and z-axis modulation for evaluation of a mass, which was seen on a standard radiograph. Mean effective tube current of 48 mAs was used, which means there was approximately 33% reduction in comparison with the reference tube current of 70 mAs. Calculated effective dose for the whole examination was 2.75 mSv. (a) Topogram shows mass (white arrows) on the right side of the thorax. (b) A 5-mm transverse CT image obtained with the lung window setting shows tumor mass (arrow) in the superior segment of the right lower lobe.

View larger version (95K): [in a new window]   Figure 2. CT scan of the cervical spine obtained in a 35-year-old-woman (height, 1.74 m; weight, 67 kg; BMI, 24.57) with angular and z-axis modulation for evaluation of cervical pain with left-side irradiation. The mean effective tube current was 45 mAs, which was a dose reduction of nearly 75% in comparison with the reference tube current of 175 mAs. Calculated effective dose for the whole examination was only 0.54 mSv. Sagittal 3-mm multiplanar reconstruction image shows small median disk protrusion at the level of the C5-6 disk (white arrow) and large herniation at the level of the C6-7 disk (black arrow).

View larger version (131K): [in a new window]   Figure 3a. Images obtained in a 63-year-old man (height, 1.70 m; weight, 84 kg; BMI, 27.74) with a history of left-sided nephrectomy for renal carcinoma 2 years earlier. CT examination of the pelvis was performed with angular and z-axis modulation for evaluation of low abdominal pain. Mean effective tube current was 110 mAs, which was 5% greater than the reference tube current of 105 mAs. Calculated effective dose of the examination was 6.61 mSv. (a) Topogram shows surgical clips after left-sided nephrectomy (arrows). (b) A 5-mm transverse CT image shows metastatic osteolytic bone lesions in the left side of the ilium and sacrum (arrows).

View larger version (124K): [in a new window]   Figure 3b. Images obtained in a 63-year-old man (height, 1.70 m; weight, 84 kg; BMI, 27.74) with a history of left-sided nephrectomy for renal carcinoma 2 years earlier. CT examination of the pelvis was performed with angular and z-axis modulation for evaluation of low abdominal pain. Mean effective tube current was 110 mAs, which was 5% greater than the reference tube current of 105 mAs. Calculated effective dose of the examination was 6.61 mSv. (a) Topogram shows surgical clips after left-sided nephrectomy (arrows). (b) A 5-mm transverse CT image shows metastatic osteolytic bone lesions in the left side of the ilium and sacrum (arrows).

View larger version (122K): [in a new window]   Figure 4. Image obtained in a 65-year-old woman (height, 1.65 m; weight, 66 kg; BMI, 24.24). A CT multiphase image of the superior abdomen was obtained with angular and z-axis modulation for clinical history of recurrent pancreatitis. A mean effective tube current of 58 mAs was used in the arterial phase, and a mean effective tube current of 59 mAs was used in venous phase. This means there was a 35% and 38% reduction in tube current compared with the reference tube currents of 90 mAs and 95 mAs, respectively. Calculated effective dose for the whole examination was 14.3 mSv. Transverse 5-mm CT image obtained in the arterial phase shows multiple small pancreas pseudocysts (arrows).

View larger version (136K): [in a new window]   Figure 5. CT image obtained in a 45-year-old woman (height, 1.71 m; weight, 63 kg; BMI, 21.55) with severe low back pain and left-sided ischiatiform pain. CT lumbar spinal image obtained with angular and z-axis modulation and a mean effective tube current of 92 mAs (mean reduction of 54% in comparison with a reference tube current of 200 mAs). Calculated effective dose for the whole examination is 5.56 mSv. Sagittal 3-mm multiplanar reconstruction image shows large descending disk herniation (black arrow).

View larger version (28K): [in a new window]   Figure 6a. Graphs show correlation between mean effective tube current and BMI of patients who underwent CT scanning with angular and z-axis modulation in the (a) thorax, (b) pelvis, (c) lumbar spine (normal-sized patients), and (d) lumbar spine (large or obese patients).

View larger version (31K): [in a new window]   Figure 6b. Graphs show correlation between mean effective tube current and BMI of patients who underwent CT scanning with angular and z-axis modulation in the (a) thorax, (b) pelvis, (c) lumbar spine (normal-sized patients), and (d) lumbar spine (large or obese patients).

View larger version (30K): [in a new window]   Figure 6c. Graphs show correlation between mean effective tube current and BMI of patients who underwent CT scanning with angular and z-axis modulation in the (a) thorax, (b) pelvis, (c) lumbar spine (normal-sized patients), and (d) lumbar spine (large or obese patients).

View larger version (29K): [in a new window]   Figure 6d. Graphs show correlation between mean effective tube current and BMI of patients who underwent CT scanning with angular and z-axis modulation in the (a) thorax, (b) pelvis, (c) lumbar spine (normal-sized patients), and (d) lumbar spine (large or obese patients).

View larger version (27K): [in a new window]   Figure 7a. Graphs show correlation between mean effective tube current and BMI in patients who underwent CT scanning with angular and z-axis modulation in the (a) cervical spine and (b) abdomen-liver. Graphs also show correlation between mean effective tube current and weight in patients who underwent CT scanning with angular and z-axis modulation in the (c) cervical spine and (d) abdomen-liver.

View larger version (29K): [in a new window]   Figure 7b. Graphs show correlation between mean effective tube current and BMI in patients who underwent CT scanning with angular and z-axis modulation in the (a) cervical spine and (b) abdomen-liver. Graphs also show correlation between mean effective tube current and weight in patients who underwent CT scanning with angular and z-axis modulation in the (c) cervical spine and (d) abdomen-liver.

View larger version (26K): [in a new window]   Figure 7c. Graphs show correlation between mean effective tube current and BMI in patients who underwent CT scanning with angular and z-axis modulation in the (a) cervical spine and (b) abdomen-liver. Graphs also show correlation between mean effective tube current and weight in patients who underwent CT scanning with angular and z-axis modulation in the (c) cervical spine and (d) abdomen-liver.

View larger version (29K): [in a new window]   Figure 7d. Graphs show correlation between mean effective tube current and BMI in patients who underwent CT scanning with angular and z-axis modulation in the (a) cervical spine and (b) abdomen-liver. Graphs also show correlation between mean effective tube current and weight in patients who underwent CT scanning with angular and z-axis modulation in the (c) cervical spine and (d) abdomen-liver.