64-Slice Multidetector Row Computed Tomographic Angiography of Aortoiliac and Lower Extremity Arteries: Efficacy of Test Injection Using a Monitoring Scan at Knee Level

Low-Voltage, High-Pitch Computerized Tomography Angiography of the Infrarenal Aorta and Lower Extremity Vessels: Assessment of Radiation Dose, Image Quality With Hybrid Iterative Reconstruction, and Efficacy of Test Injection Using a Monitoring Scan at Knee Level

OBJECTIVES

Our aim was to assess image quality and radiation dose of low-voltage high-pitch computed tomography angiography of the infrarenal aorta and lower extremities and evaluate the efficacy of test injection technique using a monitoring scan at knee level.

METHODS

A total of 60 patients with suspected peripheral arterial disease were divided into 2 groups: group 1 (30 patients, 80 kVp, high pitch [3.2], and hybrid iterative reconstruction [sinogram-affirmed iterative reconstruction]) and group 2 (30 patients, 120 kVp, low pitch [1.0], and filtered back projection reconstruction). The test injection technique at knee level was used to determine the scan delay time in group 1. The image quality and radiation exposure were compared.

RESULTS

There were significant differences between the 2 groups in mean (SD) arterial attenuation (80 vs 120 kVp: 507.78 [103.01] vs 317.54 [62.03] Hounsfield units, P < 0.001), mean (SD) signal-to-noise ratio (51.04 [20.29] vs 34.66 [9.94], P < 0.001), and contrast-to-noise ratio (44.83 [17.93] vs 28.26 [9.60], P < 0.001). No difference in subjective image quality was found between the 2 groups (all P > 0.05). The imaging time was significantly shorter in group 1 (2.70 [0.11] vs 14.65 [0.90s], P < 0.001). The mean (SD) effective dose was significantly lower in the 80 kVp group (0.76 [0.06] vs 4.29 [0.63] mSv, P < 0.001).

CONCLUSIONS

The 80-kVp high-pitch computed tomography angiography of the lower limbs using sinogram-affirmed iterative reconstruction yields reduction of radiation exposure as well as obtains acceptable image quality if acquisition protocols are used in conjunction with the test injection technique using monitoring scan at knee level to determine the delay time.

Low contrast volume run-off CT angiography with optimized scan time based on double-level test bolus technique--feasibility study

PURPOSE

To verify the technical feasibility of low contrast volume (40 mL) run-off CT angiography (run-off CTA) with the individual scan time optimization based on double-level test bolus technique.

MATERIALS AND METHODS

A prospective study of 92 consecutive patients who underwent run-off CTA performed with 40 mL of contrast medium (injection rate of 6 mL/s) and optimized scan times on a second generation of dual-source CT. Individual optimized scan times were calculated from aortopopliteal transit times obtained on the basis of double-level test bolus technique--the single injection of 10 mL test bolus and dynamic acquisitions in two levels (abdominal aorta and popliteal arteries). Intraluminal attenuation (HU) was measured in 6 levels (aorta, iliac, femoral and popliteal arteries, middle and distal lower-legs) and subjective quality (3-point score) was assessed. Relations of image quality, test bolus parameters and arterial circulation involvement were analyzed.

RESULTS

High mean attenuation (HU) values (468; 437; 442; 440; 342; 274) and quality score in all monitored levels was achieved. In 91 patients (0.99) the sufficient diagnostic quality (score 1-2) in aorta, iliac and femoral arteries was determined. A total of 6 patients (0.07) were not evaluable in distal lower-legs. Only the weak indirect correlation of image quality and test-bolus parameters was proved in iliac, femoral and popliteal levels (r values: -0.263, -0.298 and -0.254). The statistically significant difference of the test-bolus parameters and image quality was proved in patients with occlusive and aneurysmal disease.

CONCLUSION

We proved the technical feasibility and sufficient quality of run-off CTA with low volume of contrast medium and optimized scan time according to aortopopliteal transit time calculated from double-level test bolus.

Uniform vascular enhancement of lower-extremity artery on CT angiography using test-injection monitoring at the central level of the scan range: a simulation flow phantom study with clinical correlation

RATIONALE AND OBJECTIVES

To evaluate the efficacy of variable contrast injection durations and scanning delay determined by test injection analysis of computed tomography angiography (CTA) of peripheral arteries.

MATERIALS AND METHODS

We used a flow phantom that simulates the hemodynamics in a lower extremity artery. We set the flow rate at the pump to 2.0 or 5.0 L/minute. In protocol 1, we adopted a variable contrast injection duration based on the peak enhancement time of the test injection monitoring at the central level of the scan range. In protocol 2, we adopted a fixed contrast injection duration. The scanning delay was determined with a conventional bolus-tracking technique monitoring at the top of the scan range. Mean arterial attenuation and difference between the maximum and minimum attenuation values were calculated. To verify the phantom study results, clinical study, including 16 patients was performed under protocol 1.

RESULTS

The mean attenuation values under protocols 1 and 2 were comparable (563.6 Hounsfield units [HU] and 535.0 HU, respectively) at a pump flow rate of 2.0 L/minute; at 5.0 L/minute, they were 289.4 HU and 328.8 HU. The difference between the maximum and minimum attenuation values was smaller under protocol 1 than protocol 2 (76.8 HU vs. 184.9 HU) at a pump flow of 2.0 L/minute and also smaller under protocol 1 than protocol 2 (79.7 HU vs. 203.8 HU) at 5.0 L/minute. In clinical study, the mean attenuation value was 332.6 +/- 51.9 HU, and the difference between the maximum and minimum attenuation values was 55.1 +/- 24.4 HU.

CONCLUSION

The object-specific injection duration based on test injection at the central level of the scan range provides sufficient and constant vascular enhancement at CTA.