Radiation dose reduction with application of non-linear adaptive filters for abdominal CT

Table 1 Lesion detection and subjective image quality scores for abdominal computed tomography examinations for non-linear adaptive filters processed and unprocessed image groups at four different radiation dose levels

	Baseline (200 mAs)	Unpro (150 mAs)	Pro (150 mAs)	Unpro (100 mAs)	Pro (100 mAs)	Unpro (50 mAs)	Pro (50 mAs)
No. of lesions	31	31	31	31	31	31	31
Lesion size (< 1 cm)	28	28	28	28	28	28	28
Lesion conspicuity	1	1	1	1	1	1	1
Image noise	2	3	2	4	2	5	4
Visibility of small structures	3	3	3	4	3	4	4
Image contrast	3	3	3	3	3	3	3
Diagnostic confidence	1	1	1	2	1	4	3

Image noise was lowered and visibility of small structures was enhanced with non-linear adaptive filters processing. Since discrete values cannot be averaged, the table presents the lowest or similar modal scores for lesion conspicuity, image noise, contrast and diagnostic confidence given by radiologists. Unpro: Unprocessed; Pro: Processed.

Table 2 Average objective image noise and HU values in abdominal computed tomography examinations for non-linear adaptive filters processed and unprocessed image series at four different radiation dose levels (mean ± SD)

	Baseline (200 mAs)	Unpro (150 mAs)	Pro (150 mAs)	Unpro (100 mAs)	Pro (100 mAs)	Unpro (50 mAs)	Pro (50 mAs)
Liver
Objective noise	15.5 ± 3.9	18.2 ± 4.9	14.4 ± 4.0	21.9 ± 5.6	15.7 ± 4.0	30.4 ± 9.2	18.8 ± 5.0
HU values	70.9 ± 15.0	70.5 ± 16.9	70.6 ± 16.0	71.2 ± 16.0	71.0 ± 16.0	70.1 ± 16.0	70.1 ± 16.0
Abdominal Aorta
Objective noise	17.4 ± 4.2	20.5 ± 5.4	16.0 ± 3.8	24.8 ± 6.2	18.5 ± 4.2	34.3 ± 9.3	22.0 ± 6.0
HU values	80.5 ± 29.0	81.6 ± 37.0	81.5 ± 31.0	82.0 ± 33.7	82.1 ± 33.0	80.3 ± 31.0	80.0 ± 31.0

Objective image noise was decreased in non-linear adaptive filters processed image as opposed to unprocessed image series with no significant change in average HU values. Unpro: Unprocessed; Pro: Processed.

Table 3 Weight and maximum transverse diameter distribution of number of subjects with acceptable and unacceptable subjective image noise in abdominal computed tomography examinations for unprocessed and non-linear adaptive filters processed image series at 150, 100 and 50 mAs tube current-time product levels (mean ± SD)

	Unprocessed images		Processed images
	Acceptable noise	Unacceptable noise	Acceptable noise	Unacceptable noise
150 mAs	14/19	5/19	19/19	0/19
Weight (kg)	74.5 ± 14.8	95.2 ± 11.1	79.9 ± 16.5	-
Transverse diameter (cm)	34.2 ± 4.3	42.9 ± 4.5	36.5 ± 5.8	-
100 mAs	4/19	15/19	17/19	2/19
Weight (kg)	77.1 ± 4.0	80.7 ± 18.6	76.9 ± 14.6	106.0 ± 4.3
Transverse diameter (cm)	32.5 ± 3.5	37.6 ± 5.9	35.7 ± 5.6	43.5 ± 0.7
50 mAs	0/19	19/19	5/19	14/19
Weight (kg)	-	79.9 ± 16.5	66.2 ± 13.0	91.4 ± 15.1
Transverse diameter (cm)	-	36.5 ± 5.8	33.0 ± 3.4	40.6 ± 6.1

Subjects with unacceptable image noise in processed images were significantly heavier and had greater transverse diameter than subjects with acceptable image noise.