Reduced Iodine Load at CT Pulmonary Angiography with Dual-Energy Monochromatic Imaging: Comparison with Standard CT Pulmonary Angiography—A Prospective Randomized Trial
Ren YuanWilliam P. ShumanJames P. EarlsCameron HagueHina A. MumtazAndrew Scott-MoncrieffJennifer D. EllisJohn R. MayoJonathon Leipsic
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To compare quantitative and subjective image quality and radiation dose between standard computed tomographic (CT) pulmonary angiography (CTPA) and CTPA with a dual-energy technique with reduced iodine load.This prospective study was approved by the institutional review board and each participant provided informed consent. Ninety-four patients (59% male; mean age ± standard deviation, 62 years ± 15) were randomized to one of two protocols: standard CTPA (100-120 kVp) with standard contrast medium injection (n = 46) and dual-energy CTPA (image reconstruction at 50 keV) with the same injection volume as in the standard protocol but composed of contrast medium and saline in a 1:1 fashion, resulting in 50% reduction in iodine load (n = 48). Signal intensity and noise in three central and two segmental pulmonary arteries were measured; signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were calculated. A five-point scale was used to subjectively evaluate vascular enhancement and image noise. The proportion of diagnostic (score, ≥ 3) studies and the interreader agreement regarding the dichotomized diagnostic versus nondiagnostic scale were compared between the two groups.Compared with standard CTPA, dual-energy CTPA demonstrated higher signal intensity in all pulmonary arteries (all P < .01), inferior noise only in segmental arteries (P < .05), higher SNR and CNR (both P < .05), and compatible effective dose (P > .05). The five-point score was higher in the standard CTPA protocol (P < .05). The interreader agreement regarding the dichotomized diagnostic versus nondiagnostic scale was similar (P > .05) between the two groups.Dual-energy CTPA with image reconstruction at 50 keV allows a significant reduction in iodine load while improving intravascular signal intensity, maintaining SNR and with comparable radiation dose.Keywords:
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Pulmonary angiography
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To derive and validate a practical patient-specific dose protocol to obtain an image quality, expressed by the image noise, independent of patients’ size and a better radiation dose justification in coronary CT angiography (CCTA) using prospective ECG triggering. 43 patients underwent clinically indicated CCTA. The image noise, defined as the standard deviation of pixel attenuation values in a homogeneous region in the liver, was determined in all scans. Subsequently, this noise was normalized to the radiation exposure. Next, three patient-specific parameters, body weight, body mass index and mass per length (MPL), were tested for the best correlation with normalized image noise. From these data, a new dose protocol to provide a less variable image noise was derived and subsequently validated in 84 new patients. The normalized image noise increased for heavier patients for all patients’ specific parameters (p < 0.001). MPL correlated best with the normalized image noise and was selected for dose protocol optimization. This new protocol resulted in image noise levels independent of patients’ MPL (p = 0.28). A practical method to obtain CCTA images with noise levels independent of patients’ MPL was derived and validated. It results in a less variable image quality and better radiation exposure justification and can also be used for CT scanners from other vendors.
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Radiation exposure is one of the major limitations of computed tomographic coronary angiography (CTA). The purpose of this study was to compare the objective and subjective image quality and radiation dose using prospective ECG gating (PGA) versus ECG-controlled tube current modulation (ECTCM) scanning techniques.A prospective, single-center study was performed at Prince Sultan Cardiac Centre, Qassim, Saudi Arabia. A total of 104 patients with low-to- intermediate probability of coronary artery disease (CAD) underwent CTA with either PGA or ECTCM acquisition. PGA was performed during the study period and compared with the last 50 CTAs previously done using ECTCM. A 4-point scale was used to assess the image quality subjectively. Objective image quality was assessed using image signal, noise, and signal-to-noise ratio (SNR).Patient's Baseline characteristics were not different between the two scanning protocols. The 4-point score of subjective image quality showed no significant differences between the PGA and ECTCM scans (2.9 ± 0.7, 2.96 ± 0.7, respectively; p = 0.87). The objective image quality showed significantly higher noise and lower SNR with PGA compared with ECTCM (31 ± 9, 27 ± 9, respectively; p < 0.001 for noise) and (15 ± 5, 17 ± 7, respectively; p < 0.001 for SNR), with no statistical difference in the image signal (434 ± 123, 425 ± 103 HU, respectively, p = 0.7). Radiation exposure was significantly lower with PGA than with ECTCM. The dose-length product (DLP) for PGA was 334 ± 130 mGy, compared with 822 ± 286 mGy for the ECTCM. This corresponds to a 59% reduction in radiation exposure (p < 0.0001).Although prospective ECG-triggered axial scanning increased image noise, it maintained subjective image quality and was associated with a 59% reduction in radiation exposure when compared with ECTCM.
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To develop an algorithm for selecting tube current for computed tomography (CT), based on patient weight, that produces abdominal CT images of consistent image quality.We recorded body weight and radiation exposure parameters for 37 patients undergoing abdominal CT. Two radiologists blind to the CT technique independently graded 11 measures of image quality, using a 5-point (5 = excellent, 4 = good, 3 = acceptable, 2 = poor, and 1 = unacceptable) scale. These scores were averaged to generate an overall image quality score. Using linear regression, we found a target image noise level that corresponded to an overall image quality score of 4.5. We measured CT image noise in 9 uniformly attenuating regions of interest in the liver and abdominal aorta. We used linear regression to assess the relation between tube current and image noise. A prediction equation was developed to set the tube current in different-sized patients to produce images at the target noise level. Finally, we calculated the dose savings that would have resulted with this tube-current selection technique.Image noise was correlated with patient weight (r2 = 0.81). At an overall image quality score of 4.5, the noise was 16 HU. Using this target noise value, we determined the required tube current for each patient weight and found that the use of this technique would have reduced radiation exposure for all patients weighing less than 70 kg. The dose reduction for the smallest patient (35.4 kg) was 72%.To produce CT scans of similar quality, a simple prediction equation can be developed for any scanner to optimize radiation dose for patients of all body weights.
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Dynamic X-ray imaging systems are used for interventional cardiac procedures to treat coronary heart disease. X-ray settings are controlled automatically by specially-designed X-ray dose control mechanisms whose role is to ensure an adequate level of image quality is maintained with an acceptable radiation dose to the patient. Current commonplace dose control designs quantify image quality by performing a simple technical measurement directly from the image. However, the utility of cardiac X-ray images is in their interpretation by a cardiologist during an interventional procedure, rather than in a technical measurement. With the long term goal of devising a clinically-relevant image quality metric for an intelligent dose control system, we aim to investigate the relationship of image noise with clinical professionals' perception of dynamic image sequences. Computer-generated noise was added, in incremental amounts, to angiograms of five different patients selected to represent the range of adult cardiac patient sizes. A two alternative forced choice staircase experiment was used to determine the amount of noise which can be added to a patient image sequences without changing image quality as perceived by clinical professionals. Twenty-five viewing sessions (five for each patient) were completed by thirteen observers. Results demonstrated scope to increase the noise of cardiac X-ray images by up to 21% ± 8% before it is noticeable by clinical professionals. This indicates a potential for 21% radiation dose reduction since X-ray image noise and radiation dose are directly related; this would be beneficial to both patients and personnel.
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To investigate whether an adaptive statistical iterative reconstruction (ASIR) algorithm improves the image quality at low-tube-voltage (80-kVp), high-tube-current (675-mA) multidetector abdominal computed tomography (CT) during the late hepatic arterial phase.This prospective, single-center HIPAA-compliant study was institutional review board approved. Informed patient consent was obtained. Ten patients (six men, four women; mean age, 63 years; age range, 51-77 years) known or suspected to have hypervascular liver tumors underwent dual-energy 64-section multidetector CT. High- and low-tube-voltage CT images were acquired sequentially during the late hepatic arterial phase of contrast enhancement. Standard convolution FBP was used to reconstruct 140-kVp (protocol A) and 80-kVp (protocol B) image sets, and ASIR (protocol C) was used to reconstruct 80-kVp image sets. The mean image noise; contrast-to-noise ratio (CNR) relative to muscle for the aorta, liver, and pancreas; and effective dose with each protocol were assessed. A figure of merit (FOM) was computed to normalize the image noise and CNR for each protocol to effective dose. Repeated-measures analysis of variance with Bonferroni adjustment for multiple comparisons was used to compare differences in mean CNR, image noise, and corresponding FOM among the three protocols. The noise power spectra generated from a custom phantom with each protocol were also compared.When image noise was normalized to effective dose, protocol C, as compared with protocols A (P = .0002) and B (P = .0001), yielded an approximately twofold reduction in noise. When the CNR was normalized to effective dose, protocol C yielded significantly higher CNRs for the aorta, liver, and pancreas than did protocol A (P = .0001 for all comparisons) and a significantly higher CNR for the liver than did protocol B (P = .003). Mean effective doses were 17.5 mSv +/- 0.6 (standard error) with protocol A and 5.1 mSv +/- 0.3 with protocols B and C. Compared with protocols A and B, protocol C yielded a small but quantifiable noise reduction across the entire spectrum of spatial frequencies.Compared with standard FBP reconstruction, an ASIR algorithm improves image quality and has the potential to decrease radiation dose at low-tube-voltage, high-tube-current multidetector abdominal CT during the late hepatic arterial phase.
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X-ray-computed tomography (CT) has become one of the most important investigation procedures worldwide. The study aimed to assess image quality parameters, mainly noise, and radiation doses during abdominal examination. This study examined the diagnostic parameters (kilo voltage, tube current time product, slice thickness, and pitch) and their effects on image quality as well as the radiation doses received from computed tomography scanners using phantom. The study carried out in four CT centers in Sudan. The study applied prospective and experimental methods. The study demonstrated there was a linear correlation between diagnostic parameters and image noise. The reduction in milli-ampere second and peak kilo voltage increased the image noise. Moreover increasing the pitch led to an increase in the image noise, whereas increasing the slice thickness, reduced the image noise. There was also a linear relationship between kilo voltage and radiation dose at Elnileen diagnostic center characterized by an increase kilo voltages values which led to an increase in the radiation dose by 92% and a reduction in the image noise by 83%. However, at Antalya medical center, increasing in kilo voltage values led to an increase in the radiation dose by 35% and a reduction in the image noise by 26%. Also increasing in milli-ampere second values led to an increase in the radiation dose by 49% and a reduction in the image noise by 46% in a phantom compared with an increase in radiation dose by 82% and a reduction in the image noise by 51% in patients .The study found that an optimal protocol for adult abdominal scan at Antalya medical center was 4.22HU for image noise and 10.45 mGy for radiation dose when using 120 kVp, 300 mAs, 5 mm slice thickness and pitch of 0.8. At Elnileen diagnostic center, however, the optimal protocol was 5.4 HU for image noise and 5.4 mGy for radiation dose using 130 kVp, 50 mAs, 10 mm slice thickness and pitch of 2. In addition, the quality control tests for image quality parameters carried out at the two centers were performed by using the Chat Phan phantom and all the tests were within the acceptable limits, according to Sudan Atomic Energy Commission (SAEC) Standardizations. The study concludes with a number of recommendations, such as; the necessity for an extensive collaboration among manufacturers, radiologists, technologists and physicists to find a plan to decrease patient radiation dose (ALARA Principle) from computed tomography scanner.
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The purpose of this study was to evaluate and compare the effect of acquisition parameters of the abdominal computed tomography protocol on image quality and dose quantities, including contrast-to-noise ratio (CNR), noise, spatial resolution (SR) as well as volumetric computed tomography dose index (CTDIv).
The measurements have been done on a HITACHI 16-slice scanner using two phantoms (PMMA and Catphan 500), two tube voltages of 120KVp and 100KVp have been analyzed while varying the tube current settings from 155 to 300 (mAs) in order to measure the abdominal image quality quantities and dose (CTDIv).
The scanning at 100KVp compared to 120KVp has resulted in a dose reduction up to 38% at mAs ranging from 100 to 300, a decrease in CNR of 28%, a slight decrease in spatial resolution accompanied with an increase in noise.
This study has shown that despite the increase in noise at low tube voltages, it is possible to reduce the dose without affecting the quantities of spatial resolution and the contrast/noise ratio by lowering the tube voltage from 120KVp to 100KVp.
Keywords: Abdominal CT; CTDIv; Image Quality; Phantom.
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