Paradoxical Effect of Cardiac Output on Arterial Enhancement at Computed Tomography: Does Cardiac Output Reduction Simply Result in an Increase in Aortic Peak Enhancement?

OBJECTIVE: The aim of this study was to evaluate the effect of cardiac output (CO) on aortic peak enhancement using protocols with different contrast material (CM) injection durations. METHODS: We used a flow phantom that simulated the human circulatory system. Contrast material was injected at a rate of 4.0 mL/s for a period of 2.5, 5, 10, 15, or 20 seconds for a CO of 2.8, 4.2, and 5.6 L/min. Single-level serial computed tomography scans of the simulated aorta were acquired after the start of CM delivery, and aortic peak enhancement was recorded under the different injection protocols. RESULTS: Under a long injection duration protocol (20 seconds), a decrease in CO increased aortic peak enhancement proportionally (CO of 2.8 L/min, 420 Hounsfield units [HU]; CO of 4.2 L/min, 365 HU; CO of 5.6 L/min, 291 HU). However, this effect was decreased under shorter injection duration protocols (5, 10, and 15 seconds); under the shortest (2.5-second) injection duration protocol, a decrease in CO resulted in a decrease in aortic peak enhancement (CO of 2.8 L/min, 36 HU; CO of 4.2 L/min, 51 HU; CO of 5.6 L/min, 55 HU). CONCLUSIONS: The magnitude of the effect of CO on aortic peak enhancement depends on the CM injection duration.

Transluminal attenuation-gradient coronary CT angiography on a 320-MDCT volume scanner: Effect of scan timing, coronary artery stenosis, and cardiac output using a contrast medium flow phantom.

PURPOSE: Transluminal-attenuation-gradient (TAG) may reflect patient characteristics and physiological parameters. Furthermore, TAG may be affected by factors such as the CT scanner speed, scanning method, scan timing after contrast-medium (CM) injection, and the injection methods. The purpose of our study was to investigate quantitative TAG at different scan timing points after CM injection for coronary CT angiography. MATERIALS AND METHODS: Using a CM flow phantom and two types of connecting tube mimicking 0% and 70% coronary artery stenosis, we performed 320-detector volume scanning. The heart rate was set at 60bpm and cardiac-output (CO) at 2.0 and 4.0 l/min, respectively. The acquisition time repeated at 0.5-s intervals for 40 and 25s at a CO of 2.0- and 4.0 l/min. We measured the CT number on the same slice level, calculated the time-density-curve (TDC) and the TAG at each time point. RESULTS: At COs of 2.0 and 4.0 l/min at 0% stenosis, TAG exhibited smaller variations (-3.02 to +0.55HU/cm at 2.0 l/min, -2.63 to +0.43HU/cm at 4.0 l/min) than at 70% stenosis at each time point along the TDC. Compared with a CO at 2.0 l/min with 70% stenosis, the TAG curve for a CO at 4.0 l/min gradually changed with time (-6.64 to +1.18HU/cm at 2.0 l/min vs. -3.46 to +2.75HU/cm at 4.0 l/min). CONCLUSION: The TAG value was affected by scan timing after CM injection and by CO although the size of the connecting tube with and without stenosis was identical.

Low-tube-voltage selection for non-contrast-enhanced CT: Comparison of the radiation dose in pediatric and adult phantoms.

PURPOSE: We used pediatric and adult anthropomorphic phantoms to compare the radiation dose of low- and standard tube voltage chest and abdominal non-contrast-enhanced computed tomography (CT) scans. We also discuss the optimal low tube voltage for non-contrast-enhanced CT. METHODS: Using a female adult- and three differently-sized pediatric anthropomorphic phantoms we acquired chest and abdominal non-contrast-enhanced scans on a 320-multidetector CT volume scanner. The tube voltage was set at 80-, 100-, and 120 kVp. The tube current was automatically assigned on the CT scanner in response to the set image noise level. On each phantom and at each tube voltage we measured the surface and center dose using high-sensitivity metal-oxide-semiconductor field-effect transistor detectors. RESULTS: The mean surface dose of chest and abdominal CT scans in 5-year olds was 4.4 and 5.3 mGy at 80 kVp, 4.5 and 5.4 mGy at 100 kV, and 4.0 and 5.0 mGy at 120 kVp, respectively. These values were similar in our 3-pediatric phantoms (p > 0.05). The mean surface dose in the adult phantom increased from 14.7 to 19.4 mGy for chest- and from 18.7 to 24.8 mGy for abdominal CT as the tube voltage decreased from 120 to 80 kVp (p < 0.01). CONCLUSION: Compared to adults, the surface and center dose for pediatric patients is almost the same despite a decrease in the tube voltage and the low tube voltage technique can be used for non-contrast-enhanced chest- and abdominal scanning.

Simultaneous achievement of accurate CT number and image quality improvement for myocardial perfusion CT at 320-MDCT volume scanning.

PURPOSE: To investigate differences in image-to-image variations between full- and half-scan reconstruction on myocardial CT perfusion (CTP) study. METHODS: Using a cardiac phantom we performed ECG-gated myocardial CTP on a second-generation 320-multidetector CT volume scanner. The heart rate was set at 60 bpm; once per second for a total of 24 s were performed. CT images were acquired at 80- and 120 kVp and subjected to full- and half-scan reconstruction. On images acquired at the same slice level we then measured image-to-image variations, coefficients of variance (CV), and image noise. RESULTS: The image-to-image variations with full- and half-scan reconstruction were 1.3 HU vs. 27.2 HU at 80 kVp (p < 0.001) and 0.70 HU vs. 9.3 HU at 120 kVp (p < 0.001) even though the mean HU value was almost the same for both reconstruction methods. The CV of 80- and 120-kVp images of the left ventricular cavity decreased by 0.16% and 0.17%, respectively, with full-scan reconstruction; with half-scan reconstruction it decreased by 3.34% and 2.30%, respectively. Compared with half-scan reconstruction, the image noise was reduced by 27.2% at 80 kVp and by 28.0% at 120 kVp with full-scan reconstruction. CONCLUSION: Myocardial CTP with full-scan reconstruction substantially decreased image-to-image variations and provided accurate CT attenuation.

Automatic exposure control at single- and dual-heartbeat CTCA on a 320-MDCT volume scanner: effect of heart rate, exposure phase window setting, and reconstruction algorithm.

PURPOSE: To investigate whether electrocardiogram (ECG)-gated single- and dual-heartbeat computed tomography coronary angiography (CTCA) with automatic exposure control (AEC) yields images with uniform image noise at reduced radiation doses. MATERIALS AND METHODS: Using an anthropomorphic chest CT phantom we performed prospectively ECG-gated single- and dual-heartbeat CTCA on a second-generation 320-multidetector CT volume scanner. The exposure phase window was set at 75%, 70-80%, 40-80%, and 0-100% and the heart rate at 60 or 80 or corr80 bpm; images were reconstructed with filtered back projection (FBP) or iterative reconstruction (IR, adaptive iterative dose reduction 3D). We applied AEC and set the image noise level to 20 or 25 HU. For each technique we determined the image noise and the radiation dose to the phantom center. RESULTS: With half-scan reconstruction at 60 bpm, a 70-80% phase window- and a 20-HU standard deviation (SD) setting, the imagenoise level and -variation along the z axis manifested similar curves with FBP and IR. With half-scan reconstruction, the radiation dose to the phantom center with 70-80% phase window was 18.89 and 12.34 mGy for FBP and 4.61 and 3.10 mGy for IR at an SD setting SD of 20 and 25 HU, respectively. At 80 bpm with two-segment reconstruction the dose was approximately twice that of 60 bpm at both SD settings. However, increasing radiation dose at corr80 bpm was suppressed to 1.39 times compared to 60 bpm. CONCLUSION: AEC at ECG-gated single- and dual-heartbeat CTCA controls the image noise at different radiation dose.

Coronary artery stent evaluation by combining iterative reconstruction and high-resolution kernel at coronary CT angiography.

PURPOSE: To evaluate stent lumen visualization by combining high-resolution cardiac kernel and the iterative reconstruction (iDose) on an anthropomorphic moving heart phantom and in patients at coronary computed tomography (CT) angiography. MATERIALS AND METHODS: We used the moving heart phantom and a 64 detector-row CT, retrospectively gated helical scanning, and image reconstruction. The heart rate was set at nonpulsating condition of 0 beats/min, 50 beats/min, and 80 beats/min. The 120-kV images were reconstructed in synchronization with electrocardiogram data using filtered back projection (FBP) or iDose algorithm and standard kernel/filter (CB) or high-resolution kernel/filter (CD). We measured image noise, the kurtosis, and stent lumen diameter in the phantom study. We also assessed the visual inspections by two radiologists. RESULTS: With cardiac motion at 50 and 80 beats/min, the difference of kurtosis improved with CD relative to CB (P < .05). iDose algorithm with level 7 provided lowest noise, with no statistically significance in difference of the kurtosis relative to level 4 (P > .05). Without cardiac motion at 0 beats/min, the stent lumen diameter measurements with CD kernel were better relative to CB kernel (P < .05). In addition, no significant difference was found in stent lumen diameter between iDose level 4 and level 7 (P > .05). CONCLUSION: The use of iDose and a sharp kernel allowed improved stent visualization at a lower radiation dose.

Improvement of image quality at low-radiation dose and low-contrast material dose abdominal CT in patients with cirrhosis: intraindividual comparison of low tube voltage with iterative reconstruction algorithm and standard tube voltage.

OBJECTIVE: To intraindividually compare a low-tube voltage, low-contrast material dose computed tomography (CT) reconstructed with iterative reconstruction (IR) algorithm at standard tube voltage reconstructed with filtered back projection (FBP) and standard-contrast material dose during liver dynamic CT. MATERIALS AND METHODS: Twenty-five patients with liver cirrhosis underwent 64-section multidetector CT. One hundred twenty kilovolt (peak) (kV[p]) with standard contrast material dose of 600 mg of iodine per kilogram (protocol A) and 80 kV(p) with low-contrast material dose of 450 mg of iodine per kilogram (protocol B) CT image sets were reconstructed by using FBP algorithm and that of using IR algorithm with a 60%/40% blend of IR-FBP reconstruction at 80-kV(p) image set (protocol C). Scans obtained during 3 hepatic phases were subjected to quantitative and qualitative analysis. RESULTS: The mean radiation dose and the contrast medium dose were significantly lower under protocols B and C than under protocol A. In all hepatic phases, all signal-to-noise and contrast-to-noise ratios were greater under protocol C than under other protocols at all anatomic sites. Qualitative analysis showed that image noise and diagnostic acceptability were significantly higher under protocol C. CONCLUSION: In all hepatic phases, a low-tube voltage, low-contrast material dose CT with IR algorithm yielded better contrast enhancement and image quality than a standard tube voltage, standard contrast material dose CT with FBP in thin adult patients.

Evaluation of deep vein thrombosis with reduced radiation and contrast material dose at computed tomography venography: clinical application of a combined iterative reconstruction and low-tube-voltage technique.

BACKGROUND: Computed tomography venography (CTV) is clinically useful and widely available for the detection of deep vein thrombosis. Disadvantages of CTV are the need for a larger amount of i.v. contrast material (CM) and radiation exposure. A low-tube-voltage technique with iterative reconstruction may overcome this problem. The aim of this study was to investigate the effects of hybrid iterative reconstruction (HIR) on image quality at low-tube-voltage CTV. METHODS AND RESULTS: Forty patients (26 women, 14 men; mean age, 59.2±18.3 years) underwent CTV under an 80- or 120-kV protocol (CT dose index volume=10.3 mGy vs. 14.9 mGy, CM dose=540 mgI/kg vs. 690 mgI/kg) on a 64-detector CT. Quantitative parameters (ie, venous attenuation, image noise, and contrast-to-noise ratio [CNR]) were calculated and the image quality was scored on a 4-point scale. In step 1, the 80- and 120-kV protocols were compared under filtered back projection (FBP). In step 2, the 80-kV protocol with HIR was compared with the 120-kV protocol with FBP. In step 1, the visual scores were significantly higher under the 120-kV protocol; there was no significant difference in CNR between the protocols. In step 2, CNR was significantly higher under the 80-kV protocol with HIR than the 120-kV protocol with FBP. The visual scores of the 2 protocols were comparable. CONCLUSIONS: The 80-kV CTV with HIR allows for a reduction in the radiation dose by 30% and the CM dose by 20% without image quality degradation.

Improvement of low-contrast detectability in low-dose hepatic multidetector computed tomography using a novel adaptive filter: evaluation with a computer-simulated liver including tumors.

PURPOSE: The purpose of this study was to investigate how much radiation dose can be reduced without loss of low-contrast detectability with a newly developed adaptive noise reduction filter in hepatic multidetector computed tomography (MDCT) scans by using a computer-simulated liver phantom. MATERIALS AND METHODS: Simulated CT images, including liver and intrahepatic tumors, were mathematically constructed using a computer workstation to evaluate low-contrast detectability by the observer performance test. Milliampere second for construction of simulated images were 60, 80, 100, and 120 mAs (low dose) and 160 mAs (standard dose) at 120 kVp. Images with 60, 80, 100, and 120 mAs were postprocessed with the adaptive noise reduction filter. A total of 432 images were prepared and receiver operating characteristic (ROC) analysis was performed by 5 radiologists. The detectability of simulated tumor by radiologists was estimated with the area under the ROC curves (Az values). In addition, we visually evaluated CT images of 15 patients with chronic liver damage for graininess of the liver parenchyma, sharpness of the liver contour, conspicuity and marginal sharpness of the liver tumors, and overall image quality. RESULTS: The mean Az value at 0.777 (60 mAs), 0.828 (80 mAs), and 0.844 (100 mAs) without filter was significantly lower than that of 160 mAs without filter (P < 0.001, 60 mAs; P = 0.010, 80 mAs; P = 0.040, 100 mAs). There was no statistical difference between the mean Az value at 80 mAs with and 160 mAs without the adaptive noise reduction filter (P = 0.220) and 100 mAs with and 160 mAs without the adaptive noise reduction filter (P = 0.979). In the visual evaluation of patient livers, there was no statistical difference in the graininess and sharpness of the liver, the conspicuity and marginal sharpness of the tumor, and the overall image quality between standard-dose and filtered low-dose images (Wilcoxon signed rank test, P > 0.05). CONCLUSION: The radiation dose can be reduced by 50% without loss of nodule detectability by applying the adaptive noise reduction filter to simulated and patient liver images obtained at MDCT.