An education and training programme for radiological institutes: impact on the reduction of the CT radiation dose.

OBJECTIVES: To establish an education and training programme for the reduction of CT radiation doses and to assess this programme's efficacy. METHODS: Ten radiological institutes were counselled. The optimisation programme included a small group workshop and a lecture on radiation dose reduction strategies. The radiation dose used for five CT protocols (paranasal sinuses, brain, chest, pulmonary angiography and abdomen) was assessed using the dose-length product (DLP) before and after the optimisation programme. The mean DLP values were compared with national diagnostic reference levels (DRLs). RESULTS: The average reduction of the DLP after optimisation was 37% for the sinuses (180 vs. 113 mGycm, P < 0.001), 9% for the brain (982 vs. 896 mGycm, P < 0.05), 24% for the chest (425 vs. 322 mGycm, P < 0.05) and 42% for the pulmonary arteries (352 vs. 203 mGycm, P < 0.001). No significant change in DLP was found for abdominal CT. The post-optimisation DLP values of the sinuses, brain, chest, pulmonary arteries and abdomen were 68%, 10%, 20%, 55% and 15% below the DRL, respectively. CONCLUSIONS: The education and training programme for radiological institutes is effective in achieving a substantial reduction in CT radiation dose.

Effect of beam hardening on arterial enhancement in thoracoabdominal CT angiography with increasing patient size: an in vitro and in vivo study.

PURPOSE: To assess the effect of beam hardening on arterial enhancement in thoracoabdominal computed tomographic (CT) angiography in various body sizes in a phantom and in a clinical study. MATERIALS AND METHODS: An abdominal aortic phantom was placed in three cylindrical water containers simulating a small, an intermediate, and a large patient (diameters of 22, 30, and 40 cm, respectively). CT scanning was performed at 80, 100, and 120 kVp, and aortic attenuation was assessed. In a HIPAA-compliant institutional review board-approved study with waiver of informed consent, thoracoabdominal aortic attenuation was assessed in 100 consecutive patients (75 men, 25 women; mean body weight (BW), 79 kg) undergoing thoracoabdominal 64-section CT angiography at 80 kVp. Overall aortic attenuation in patients grouped according to BW (small patients [n = 26], <70 kg; intermediate patients [n = 41], 70-85 kg; large patients [n = 33], >85 kg) was compared. Overall aortic attenuation was correlated with BW, height, body mass index (BMI), body surface area (BSA), and lateral diameter by using linear regression. RESULTS: Comparison of the intermediate- and large-phantom groups relative to the small-phantom group indicated that mean aortic attenuation decreased by 9.7% and 13.4% at 80 kVp, 9.8% and 15.1% at 100 kVp, and 13.8% and 23.8% at 120 kVp, respectively (P < .001). In the clinical study, the overall aortic attenuation decreased by 11.3% and 20.0% in the intermediate- and large-patient groups relative to the small-patient group, respectively (P < .05). Overall aortic attenuation correlated well with BSA (R = -0.454), height (R = -0.421), and BW (R = -0.414), followed by lateral diameter (R = -0.291) and BMI (R = -0.211). CONCLUSION: Beam hardening may substantially contribute to reduced arterial enhancement in larger patients undergoing thoracoabdominal CT angiography. The beam-hardening effect on arterial enhancement is more pronounced at higher tube voltages.

Thoracoabdominal-aortoiliac multidetector-row CT angiography at 80 and 100 kVp: assessment of image quality and radiation dose.

OBJECTIVE: To compare image quality and radiation dose of thoracoabdominal computed tomography (CT) angiography at 80 and 100 kVp and to assess the feasibility of reducing contrast medium volume from 60 to 45 mL at 80 kVp. MATERIALS AND METHODS: This retrospective study had institutional review board approval; informed consent was waived. Seventy-five patients who had undergone thoracoabdominal 64-section multidetector-row CT angiography were divided into 3 groups of 25 patients each. Patients of groups A (tube voltage, 100 kVp) and B (tube voltage, 80 kVp) received 60 mL of contrast medium at 4 mL/s. Patients of group C (tube voltage, 80 kVp) received 45 mL of contrast medium at 3 mL/s. Mean aortoiliac attenuation, image noise, and contrast-to-noise ratio were assessed. The measurement of radiation dose was based on the volume CT dose index. Three independent readers assessed the diagnostic image quality. RESULTS: Mean aortoiliac attenuation for group B (621.1 +/- 90.5 HU) was significantly greater than for groups A and C (485.2 +/- 110.5 HU and 483.1 +/- 119.8 HU; respectively) (P < 0.001). Mean image noise was significantly higher for groups B and C than for group A (P < 0.05). The contrast-to-noise ratio did not significantly differ between the groups (group A, 35.0 +/- 13.8; group B, 31.7 +/- 10.1; group C, 27.3 +/- 11.5; P = 0.08). Mean volume CT dose index in groups B and C (5.2 +/- 0.4 mGy and 4.9 +/- 0.3 mGy, respectively) were reduced by 23.5% and 27.9%, respectively, compared with group A (6.8 +/- 0.8 mGy) (P < 0.001). The average overall diagnostic image quality for the 3 groups was graded as good or better. The score for group A was significantly higher than that for group C (P < 0.01), no difference was seen between group A and B (P = 0.92). CONCLUSIONS: Reduction of tube voltage from 100 to 80 kVp for thoracoabdominal CT angiography significantly reduces radiation dose without compromising image quality. Reduction of contrast medium volume to 45 mL at 80 kVp resulted in lower but still diagnostically acceptable image quality.

Endoleak detection with CT angiography in an abdominal aortic aneurysm phantom: effect of tube energy, simulated patient size, and physical properties of endoleaks.

PURPOSE: To analyze the detection of endoleaks with low-tube-voltage computed tomographic (CT) angiography. MATERIALS AND METHODS: A cylindrical plastic phantom mimicking an aortic aneurysm, containing a stent graft and 36 simulated endoleaks of various diameters, densities, and distances from the graft, was placed into three different water containers corresponding to small, intermediate-sized, and large patients. CT was performed at 80, 100, and 120 kVp, and the volume CT dose index (CTDI(vol)) was noted. Three radiologists independently analyzed the CT images for endoleak localization with diagnostic confidence and for image quality. Analysis of variance was used to compare results and to find parameters that have an effect on endoleak detection. RESULTS: All 6-mm endoleaks were correctly identified at all tube energies except for five endoleaks at 80 kVp in the thick phantom. Observers detected more 4-mm leaks at higher tube voltage in the thick phantom (P < .001) and at 100 kVp compared with 80 kVp in the intermediate phantom (P = .006). Compared with CTDI(vol) at 120 kVp, CTDI(vol) was lower by nearly 50% at 80 kVp in the thin and intermediate phantoms and at 100 kVp in the thick phantom. Endoleak diameter, position, phantom dimension, and tube voltage all had a significant effect on the number of detected leaks (P < .0001). CONCLUSION: This phantom study suggests that reduced radiation exposure is achievable with CT angiography at 80 kVp in small and intermediate-sized patients and at 100 kVp in large patients, with no increased risk of missing significant endoleaks measuring 6 mm or larger.

Effect of X-ray tube parameters, iodine concentration, and patient size on image quality in pulmonary computed tomography angiography: a chest-phantom-study.

OBJECTIVES: The aim of this phantom study was to evaluate the contrast-to-noise ratio (CNR) in pulmonary computed tomography (CT)-angiography for 300 and 400 mg iodine/mL contrast media using variable x-ray tube parameters and patient sizes. We also analyzed the possible strategies of dose reduction in patients with different sizes. MATERIALS AND METHODS: The segmental pulmonary arteries were simulated by plastic tubes filled with 1:30 diluted solutions of 300 and 400 mg iodine/mL contrast media in a chest phantom mimicking thick, intermediate, and thin patients. Volume scanning was done with a CT scanner at 80, 100, 120, and 140 kVp. Tube current-time products (mAs) varied between 50 and 120% of the optimal value given by the built-in automatic dose optimization protocol. Attenuation values and CNR for both contrast media were evaluated and compared with the volume CT dose index (CTDI(vol)). Figure of merit, calculated as CNR/CTDIvol, was used to quantify image quality improvement per exposure risk to the patient. RESULTS: Attenuation of iodinated contrast media increased both with decreasing tube voltage and patient size. A CTDIvol reduction by 44% was achieved in the thin phantom with the use of 80 instead of 140 kVp without deterioration of CNR. Figure of merit correlated with kVp in the thin phantom (r = -0.897 to -0.999; P < 0.05) but not in the intermediate and thick phantoms (P = 0.09-0.71), reflecting a decreasing benefit of tube voltage reduction on image quality as the thickness of the phantom increased. Compared with the 300 mg iodine/mL concentration, the same CNR for 400 mg iodine/mL contrast medium was achieved at a lower CTDIvol by 18 to 40%, depending on phantom size and applied tube voltage. CONCLUSIONS: Low kVp protocols for pulmonary embolism are potentially advantageous especially in thin and, to a lesser extent, in intermediate patients. Thin patients profit from low voltage protocols preserving a good CNR at a lower exposure. The use of 80 kVp in obese patients may be problematic because of the limitation of the tube current available, reduced CNR, and high skin dose. The high CNR of the 400 mg iodine/mL contrast medium together with lower tube energy and/or current can be used for exposure reduction.

Virtopsy: postmortem minimally invasive angiography using cross section techniques--implementation and preliminary results.

Postmortem investigation is increasingly supported by Computed Tomography (CT) and Magnetic Resonance Imaging (MRI). This led to the idea to implement a noninvasive or minimally invasive autopsy technique. Therefore, a minimally invasive angiography technique becomes necessary, in order to support the vascular cross section diagnostic. Preliminary experiments investigating different contrast agents for CT and MRI and their postmortem applicability have been performed using an ex-vivo porcine coronary model. MSCT and MRI angiography was performed in the porcine model. Three human corpses were investigated using minimally invasive MSCT angiography. Via the right femoral artery a plastic tube was advanced into the aortic arch. Using a flow adjustable pump the radiopaque contrast agent meglumine-ioxithalamate was injected. Subsequent MSCT scanning provided an excellent anatomic visualization of the human arterial system including intracranial and coronary arteries. Vascular pathologies such as calcification, stenosis and injury were detected. Limitations of the introduced approach are cases of major vessel injury and cases that show an advanced stage of decay.

Grading airway stenosis down to the segmental level using virtual bronchoscopy.

OBJECTIVE: To assess the sensitivity of noninvasive virtual bronchoscopy based on multirow detector CT scanning in detecting and grading central and segmental airway stenosis using flexible bronchoscopic findings as the reference standard. MATERIALS AND METHODS: In a blinded controlled trial, multirow detector CT virtual bronchoscopy and flexible bronchoscopy were used to search for and grade airway stenosis in 20 patients. CT scan data were obtained with a multirow detector CT scanner using 4 x 1 mm collimation. Flexible bronchoscopy findings were graded by a pulmonologist and served as the reference standard for 176 central airway regions (ie, trachea, main bronchi, and lobar bronchi) and 302 segmental airway regions. The extent of airway narrowing was categorized as grade 0 (no narrowing), grade 1 (< 50%), or grade 2 (> or =50%). RESULTS: Flexible bronchoscopy revealed 30 stenoses in the central airways and 10 in the segmental airways. Virtual bronchoscopy detected 32 stenoses in the central airways (sensitivity, 90.0%; specificity, 96.6%; accuracy, 95.5%) and 22 in the segmental airways (sensitivity, 90.0%; specificity, 95.6%; accuracy, 95.5%). The number of false-positive findings was higher in the segmental airways (13 false-positive findings) than in the central airways (5 false-positive findings), which caused a lower positive predictive value for the segmental airways (40.9%) than for the central airways (84.4%). Flexible and virtual bronchoscopic gradings correlated better for central airway stenosis (r = 0.87) than for segmental airway stenosis (r = 0.61). CONCLUSION: Although a high sensitivity was found for the detection of both central and segmental airway stenosis, the number of false-positive findings was higher for segmental airways. However, noninvasive multirow detector CT virtual bronchoscopy enables high-resolution endoluminal imaging of the airways down to the segmental bronchi.