Implementation of Automated Tube Current Modulation in PET/CT: Prospective Selection of a Noise Index and Retrospective Patient Analysis to Ensure Image Quality

James Jackson; Tinsu Pan; Elena Tonkopi; Nancy Swanston; Homer A. Macapinlac; Eric M. Rohren

doi:10.2967/jnmt.110.075283

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FIGURE 1.
ROIs in patient's thorax for SD measurement with minimal area of 200 mm²: axial slice in aortic arch (A), descending aorta above liver in coronal view (B), and descending aorta at level of liver (C).
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FIGURE 2.
ROIs in patient's liver for SD measurement with minimal area of 200 mm²: dome of liver (A), middle level of liver, where no lung tissue can be seen (B), and tail of liver (C).
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FIGURE 3.
Average noise (mean of SDs of CT numbers in HU) in CT images at various NI settings for phantom acquisitions of 3 ROIs in thorax and 3 in liver.
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FIGURE 4.
Average image noise (SD of CT number in HU) for CT images of 3 ROIs in thorax and 3 in liver for 45 patients analyzed retrospectively and grouped according to BMI. Avg = average.
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FIGURE 5.
Physician-determined CT image quality (on scale of 1–3) according to noise level in scans of thorax (A) and scans of liver (B). Black lines indicate best-fit linear functions for data.
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FIGURE 6.
Average decrease in tube current by patient BMI group in CT scans using ATCM with NI of 20 compared with fixed tube current of 300 mA.
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FIGURE 7.
Average image noise (SD of CT number in HU) in CT images of liver; n = 7 for each BMI range. Noise levels were not markedly different for patients with BMIs < 28 whose examinations had tube current modulation.

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TABLE 1

Noise Levels in Thorax CT Images Using ATCM and NI of 20 in Patients with BMI ≤ 28

	Noise (SD of CT number in HU)
Patient no.	ROI 1	ROI 2	ROI 3	Mean
1	11.7	9.3	12.9	11.3
2	8.0	9.1	12.3	9.8
3	8.5	14	10.5	11.0
4	9.1	11.1	10.4	10.2
5	7.1	10.2	11.9	9.7
6	8.9	9.7	13.7	10.8
7	9.1	8.4	12.6	10.0
8	9.1	12	11.6	10.9
9	10.0	12.4	13.1	11.8
10	7.0	9.4	12.7	9.7
11	9.4	11.3	13.2	11.3
12	8.4	11	11.0	10.1
13	7.0	12.2	14.4	11.2
14	8.0	9.4	12.3	9.9
15	7.3	10.8	12.2	10.1
16	10.6	12.3	12.3	11.7
17	10.8	10.6	11.0	10.8
18	9.7	12.5	13.7	12.0
19	9.3	11.8	14.0	11.7
20	9.8	13.3	12.7	11.9
21	7.5	10.3	12.4	10.1
22	9.5	12.1	9.3	10.3
Mean noise in all thorax scans				10.7