Comparison of acquisition and iterative reconstruction parameters in abdominal computed tomography-guided procedures: a phantom study

Abstract

Background: Many computed tomography (CT) navigation systems have been developed to help radiologists improve the accuracy and safety of the procedure. We evaluated the accuracy of one CT computer-assisted guided procedure with different reduction dose protocols.

Methods: A total of 128 punctures were randomly made by two operators on two different anthropomorphic phantoms. The tube voltage was fixed to 100 kVp. Tube currents (mAs) were defined to obtain 4 dose levels: 180 mAs (D1.00), 90 mAs (D0.50), 45 mAs (D0.25) and 15 mAs (D0.10) with respective volume CT dose index (CTDIvol) of 7.02, 3.52, 1.75 and 0.59 mGy. The raw data were reconstructed using level 2 of advanced model-based iterative reconstruction (ADMIRE) (A2) for D1.00, A3 for D0.50, A4 for D0.25 and A5 for D0.10. Two 12-mm targets per phantom were selected. The mean Euclidean distance (EuD) between the tip of the needle and the isocenter of the target was measured for each puncture. The different measures were compared by paired Student's t-tests.

Results: The mean EuD was 7.0±3.1 mm for the 128 punctures performed. Regardless of which phantom was considered, no significant difference in accuracy occurred between the 4 dose levels, which were 7.1±3.5 mm for D1.00; 7.1±3.1 mm for D0.50; 7.2±3.0 mm for D0.25 and 6.6±2.6 mm for D0.10.

Conclusions: Abdominal CT-guided procedures, using computer-assisted navigation and iterative reconstruction algorithms, allow precise punctures on anthropomorphic phantoms with a dose reduction of -92% compared to a standard protocol.

Keywords: Imaging guided biopsy; computer-assisted; image reconstruction; low-dose computed tomography (low-dose CT); noise reduction.

Figure 1

The two phantoms used in the study. Phantom 1 is depicted on the left (A) with hyperdense targets (white arrowhead) and the Imactis^® magnetic transmitter (white asterisk). Phantom 2 is depicted on the right (B) with hypodense targets (black arrowhead).

Figure 2

Phantoms with the four dose levels: D1.00 with ADMIRE 2, D0.50 with ADMIRE 3, D0.25 with ADMIRE 4 and D0.10 with ADMIRE 5. Left: phantom 1; right: phantom 2. D1.00: 180 mAs, CTDI_vol =7.02 mGy; D0.50: 90 mAs, CTDI_vol =3.52 mGy; D0.25: 45 mAs, CTDI_vol =1.75 mGy; D0.10: 15 mAs, CTDI_vol =0.59 mGy. ADMIRE, advanced model-based iterative reconstruction; CTDI_vol, volume computed tomography dose index.

Figure 3

Example of simple obliquity (SO) and double obliquity (DO) punctures on phantom 2 with pre- and postprocedural CT at the four different dose levels. Windowing was adopted to show the needle tip. The artifacts differ between SO and DO punctures. D1.00: 180 mAs, CTDI_vol =7.02 mGy; D0.50: 90 mAs, CTDI_vol =3.52 mGy; D0.25: 45 mAs, CTDI_vol =1.75 mGy; D0.10: 15 mAs, CTDI_vol =0.59 mGy. CTDI_vol, volume computed tomography dose index; DO, double obliquity; SO, simple obliquity.

Figure 4

Boxplot of the mean Euclidean distance (mm) between the isocenter of the 12 mm target and the tip of the needle according to the protocol used. D1.00: 180 mAs, CTDI_vol =7.02 mGy; D0.50: 90 mAs, CTDI_vol =3.52 mGy; D0.25: 45 mAs, CTDI_vol =1.75 mGy; D0.10: 15 mAs, CTDI_vol =0.59 mGy. P value lower than 0.05 was considered significant. CTDI_vol, volume computed tomography dose index.

Figure 5

Boxplot of the mean Euclidean distance (mm) between the isocenter of the 12 mm target and the tip of the needle as a function of obliquity, target depth, phantom and operator experience. P value lower than 0.05 was considered significant.

Figure 6

Mean procedure time (s) for both operators according to the protocol used. D1.00: 180 mAs, CTDI_vol =7.02 mGy; D0.50: 90 mAs, CTDI_vol =3.52 mGy; D0.25: 45 mAs, CTDI_vol =1.75 mGy; D0.10: 15 mAs, CTDI_vol =0.59 mGy. P value lower than 0.05 was considered significant. CTDI_vol, volume computed tomography dose index.