Low-dose Computed Tomography Pulmonary Angiography Research Articles

Application of a Deep Learning-Based Contrast-Boosting Algorithm to Low-Dose Computed Tomography Pulmonary Angiography With Reduced Iodine Load.

The aim of this study was to assess the effectiveness of a deep learning-based image contrast-boosting algorithm by enhancing the image quality of low-dose computed tomography pulmonary angiography at reduced iodine load. This study included 179 patients who underwent low-dose computed tomography pulmonary angiography with a reduced iodine load using 64 mL of a 1:1 mixture of contrast medium from January 1 to June 30, 2023. For single-energy computed tomography, the noise index was set at 15.4 to maintain a CTDIvol of <2 mGy at 80 kVp, and for dual-energy computed tomography, fast kV-switching between 80 and 140 kVp was employed with a fixed tube current of 145 mA. Images were reconstructed by 50% adaptive statistical iterative reconstruction (AR50) and a commercially available deep learning image reconstruction (TrueFidelity) package at a high strength level (TFH). In addition, AR50 images were further processed using a deep learning-based contrast-boosting algorithm (AR50-CB). Quantitative and qualitative image qualities and numbers of involved vessels with thrombus at each pulmonary artery level were compared in the 3 image types using the Friedman test and Wilcoxon signed rank test. Five hundred thirty-seven reconstructed image datasets of 179 patients were analyzed. Quantitative image analysis showed AR50-CB (30.8 ± 10.0 and 28.1 ± 9.6, respectively) had significantly higher signal-to-noise ratio and contrast-to-noise ratio values than AR50 (20.2 ± 6.2 and 17.8 ± 6.2, respectively) (P < 0.001) or TFH (28.3 ± 8.3 and 24.9 ± 8.1, respectively) (P < 0.001). Qualitative image analysis showed that contrast enhancement and noise scores of AR50-CB were significantly greater than those of AR50 (P < 0.001) and that AR50-CB enhancement scores were significantly higher than TFH enhancement scores (P < 0.001). The number of subsegmental pulmonary arteries affected by thrombus detected was significantly greater for AR50-CB (30 for AR50, 30 for TFH, and 55 for AR50-CB, P < 0.001). The use of a deep learning-based contrast-boosting algorithm improved image quality in terms of signal-to-noise ratio and contrast-to-noise ratio values and the detection of thrombi in subsegmental pulmonary arteries.

The application value of deep learning image reconstruction on improving image quality and evaluating the Qanadli embolism index of dual low-dose CT pulmonary angiography

Objective: To compare the image quality and Qanadli embolism index between deep learning image reconstruction (DLR) and adaptive statistical iterative reconstruction-veo (ASiR-V) in dual low-dose CT pulmonary angiography (CTPA) with low contrast agent dose and low radiation dose. Methods: Eighty-eight patients who underwent dual low-dose CTPA in the radiology department of the affiliated hospital of Xuzhou Medical University from October 2020 to March 2021 were retrospectively analyzed, including 44 males and 44 females, aged from 11 to 87 years (61±15 years). The CTPA examination were performed using 80 kV tube voltage and 20 ml contrast agent. The raw data were reconstructed using standard kernel DLR high level (DL-H) and ASiR-V reconstruction, respectively. The patients were divided into standard kernel DL-H group (n=88, 33 cases of positive embolism) and ASiR-V group (n=88, 36 cases of positive embolism). The CT value, image noise, signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), subjective image quality score, Qanadli embolism index, positive rate and positive Qanadli embolism index were compared between the two groups. Results: There were no statistically significant differences in CT values of the main pulmonary artery, the right pulmonary artery and the left pulmonary artery between the standard kernel DL-H group and ASiR-V group [(405.8±111.7) vs (404.0±112.0) HU, (412.9±113.1) vs (411.5±112.2) HU, (418.1±119.9) vs (415.4±118.0) HU, respectively;all P>0.05)]. The image noise of the main pulmonary artery, the right pulmonary artery and the left pulmonary artery in the standard kernel DL-H group was significantly lower than the ASiR-V group(16.6±4.7 vs 28.1±4.8, 18.3±6.1 vs 29.8±4.9, 17.6±5.6 vs 28.4±4.7, respectively;all P<0.001). The SNR and CNR of the main pulmonary artery, the right pulmonary artery and the left pulmonary artery in the standard kernel DL-H group were significantly higher than the ASiR-V group(SNR: 25.5±7.1 vs 14.5±3.9, 23.9±7.2 vs 13.9±3.4, 24.9±7.4 vs 14.8±4.1, CNR: 21.6±6.6 vs 12.3±3.9, 20.2±6.7 vs 11.8±3.4, 21.2±6.9 vs 12.6±4.1, respectively;all P<0.001). The subjective image quality score of the standard kernel DL-H group was significantly higher than the ASiR-V group (4.6 vs 3.8, P<0.001). There were no significant difference in the Qanadli embolism index, positive rate and positive Qanadli embolism index between the two groups (all P>0.05). Conclusion: Compared with ASiR-V reconstruction algorithms group, standard kernel DL-H reconstruction algorithms can significantly improve the image quality of dual low-dose CTPA.

Breast Shielding Combined With an Optimized Computed Tomography Pulmonary Angiography Pregnancy Protocol: A Special Use-Case for Shielding?

To determine the impact of breast shields on breast dose and image quality when combined with a low-dose computed tomography pulmonary angiography (CTPA) protocol for pregnancy. A low-dose CTPA protocol, with and without breast shields, was evaluated by anthropomorphic phantom and 20 prospectively recruited pregnant participants from January to October 2019. Thermoluminescent dosimeters measured surface and absorbed breast dose in the phantom and surface breast dose in participants. The Monte-Carlo method estimated the absorbed breast dose in participants. Image quality was assessed quantitatively by regions of interest analysis and subjectively by the Likert scale. Doses and image quality for CTPA alone were compared with CTPA with breast shields. Mean surface and absorbed breast dose for CTPA alone were 1.3±0.4 and 2.8±1.5mGy in participants, and 1.5±0.7 and 1.6±0.6mGy in the phantom. Shielding reduced surface breast dose to 0.5±0.3 and 0.7±0.2mGy in the phantom (66%) and study participants (48%), respectively. Absorbed breast dose reduced to 0.9±0.5mGy (46%) in the phantom.Noise increased with breast shields at lower kV settings (80 to 100kV) in the phantom; however, in study participants there was no significant difference between shield and no-shield groups for main pulmonary artery noise (no-shield: 34±9.8, shield: 36.3±7.2, P =0.56), SNR (no-shield: 11.2±3.7, shield: 10.8±2.6, P =0.74) or contrast-to-noise ratio (no-shield: 10.0±3.3, shield: 9.3±2.4, P =0.6). Median subjective image quality scores were comparable (no-shield: 4.0, interquartile range: 3.5 to 4.4, shield: 4.3, interquartile range: 4.0 to 4.5). Combining low-dose CTPA with breast shields confers additional breast-dose savings without impacting image quality and yields breast doses approaching those of low-dose scintigraphy, suggesting breast shields play a role in protocol optimization for select groups.

EFFECTS OF TEST-BOLUS AND LOW-DOSE SCAN ON CT PULMONARY ANGIOGRAPHY IMAGE QUALITY IN PATIENTS WITH DIFFERENT BODY MASS INDEXES.

This study aimed to investigate different methods of obtaining high-quality Computed Tomography pulmonary angiography (CTPA) images using low-dose scanning in patients with different body mass index (BMI) values. Sixty patients with suspected pulmonary embolism were grouped based on their BMI values (BMI < 25, designated N, and BMI ≥ 25, designated O) and were assigned to receive either test bolus (TB) or bolus tracking (BT) at conventional (C) or low (L) dose. The effective dose (ED) in the N-TB-L group was lower than in the group N-TB-C (0.56±0.05 vs. 3.78±1.16, p<0.001), with similar image quality (4.90±0.31 vs. 4.70±0.47, p=0.120). The ED in the O-TB-L group was lower than in the O-TB-C group (0.54±0.03 vs. 5.14±1.34, p<0.001), but the group O-TB-C's image quality was higher (4.65±0.59 vs. 3.95±0.89, p=0.006). Groups N-TB-L versus O-TB-L, groups N-TB-L versus N-BT-L and groups O-TB-C versus O-BT-C had similar EDs (all ps>0.05), but the image quality was different (all ps<0.05). In conclusion, the results showed that the image quality of low-dose CTPA scanning using TB was similar to that of the conventional-dose CTPA in patients with BMI < 25 but was lower in patients with BMI ≥ 25. TB was better than BT for all patients, regardless of BMI, when receiving the same ED.

A Systematic Review of Double Low-dose CT Pulmonary Angiography in Pulmonary Embolism.

The aim of this study is to perform a systematic review of the feasibility and clinical application of double low-dose CT pulmonary angiography (CTPA) in the diagnosis of patients with suspected pulmonary embolism. A total of 13 studies were found to meet selection criteria reporting both low radiation dose (70 or 80 kVp versus 100 or 120 kVp) and low contrast medium dose CTPA protocols. Lowdose CTPA resulted in radiation dose reduction from 29.6% to 87.5% in 12 studies (range: 0.4 to 23.5 mSv), while in one study, radiation dose was increased in the dual-energy CT group when compared to the standard 120 kVp group. CTPA with use of low contrast medium volume (range: 20 to 75 ml) was compared to standard CTPA (range: 50 to 101 ml) in 12 studies with reduction between 25 and 67%, while in the remaining study, low iodine concentration was used with 23% dose reduction achieved. Quantitative assessment of image quality (in terms of signal-to-noise ratio and contrast-to-noise ratio) showed that low-dose CTPA was associated with higher, lower and no change in image quality in 3, 3 and 6 studies, respectively when compared to the standard CTPA protocol. The subjective assessment indicated similar image quality in 11 studies between low-dose and standard CTPA groups, and improved image quality in 1 study with low-dose CTPA. This review shows that double low-dose CTPA is feasible in the diagnosis of pulmonary embolism with significant reductions in both radiation and contrast medium doses, without compromising diagnostic image quality.

Double low-dose computed tomography pulmonary angiography in the diagnosis of pulmonary embolism

The purpose of this study is to investigate the feasibility of double low-dose (low radiation and low contrast medium doses) computed tomography pulmonary angiography (CTPA) in the diagnosis of pulmonary embolism. This retrospective study involved analysis of 59 patients undergoing 64- and 128-slice CTPA examinations which were scanned with a pitch of 0.9 and 100 and 120 kVp, respectively, while flash mode of CTPA was done with a pitch of 3.2 and 120 kVp. There were no significant differences in image quality assessment between the low kVp and standard kVp or high-pitch CTPA protocols (p=0.181-0.186). The mean effective dose for the 100 kVp protocol was significantly lower than that for the120 kVp and the flash mode protocols (p < 0.001). The contrast medium was between 35-45 ml for the 100 and 120 kVp protocols, and 20-30 ml for the 120 kVp flash mode protocol. Double low-dose CT pulmonary angiography is feasible for detection of pulmonary embolism with acquisition of diagnostic images.

Optimization of computed tomography pulmonary angiography protocols using 3D printed model with simulation of pulmonary embolism.

Three-dimensional (3D) printing has been shown to accurately replicate anatomical structures and pathologies in complex cardiovascular disease. Application of 3D printed models to simulate pulmonary arteries and pulmonary embolism (PE) could assist development of computed tomography pulmonary angiography (CTPA) protocols with low radiation dose, however, this has not been studied in the literature. The aim of this study was to investigate optimal CTPA protocols for detection of PE based on a 3D printed pulmonary model. A patient-specific 3D printed pulmonary artery model was generated with thrombus placed in both main pulmonary arteries to represent PE. The model was scanned with 128-slice dual-source CT with slice thickness of 1 and 0.5 mm reconstruction interval. The tube voltage was selected to range from 70, 80, 100 to 120 kVp, and pitch value from 0.9 to 2.2 and 3.2. Quantitative assessment of image quality in terms of signal-to-noise ratio (SNR) was measured in the main pulmonary arteries and within the thrombus regions to determine the relationship between image quality and scanning protocols. Both two-dimensional (2D) and 3D virtual intravascular endoscopy (VIE) images were generated to demonstrate pulmonary artery and thrombus appearances. PE was successfully simulated in the 3D printed pulmonary artery model. There were no significant differences in SNR measured in the main pulmonary arteries with 100 and 120 kVp CTPA protocols (P>0.05), regardless of pitch value used. SNR was significantly lower in the high-pitch 3.2 protocols when compared to other protocols using 70 and 80 kVp (P<0.05). There were no significant differences in SNR measured within the thrombus among the 100 and 120 kVp protocols (P>0.05). For low dose 70 and 80 kVp protocols, SNR was significantly lower in the high-pitch of 3.2 protocols than that in other protocols with different pitch values (P<0.01). 2D images showed the pulmonary arteries and thrombus clearly, while 3D VIE demonstrated intraluminal appearances of pulmonary wall and thrombus in all protocols, except for the 70 kVp and pitch 3.2 protocol, with visualization of thrombus and pulmonary artery wall affected by artifact associated with high image noise. Radiation dose was reduced by up to 80% when lowering kVp from 120 to 100 and 80 kVp with use of 3.2 high-pitch protocol, without significantly affecting image quality. Low-dose CT pulmonary angiography can be achieved with use of low kVp (80 and 100) and high-pitch protocol with significant reduction in radiation dose while maintaining diagnostic images of PE. Use of high pitch, 3.2 in 70 kVp protocol should be avoided due to high image noise and poorer quality.

Patient-specific 3D printed pulmonary artery model with simulation of peripheral pulmonary embolism for developing optimal computed tomography pulmonary angiography protocols.

Computed tomography pulmonary angiography (CTPA) is the preferred imaging modality for diagnosis of patients with suspected pulmonary embolism (PE). Radiation dose associated with CTPA has been significantly reduced due to the use of dose-reduction strategies, however, investigation of low-dose CTPA with use of different kVp and pitch values has not been systematically studied. The aim of this study was to utilize a 3D printed pulmonary model with simulation of small thrombus in the pulmonary arteries for development of optimal CTPA protocols. Animal blood clots were inserted into the pulmonary arteries to simulate peripheral embolism based on a realistic 3D printed pulmonary artery model. The 3D printed model was scanned with 192-slice 3rd generation dual-source CT with 1 mm slice thickness and 0.5 mm reconstruction interval. All images were reconstructed with advanced modelled iterative reconstruction (IR) at a strength level of 3. CTPA scanning parameters were as follows: 70, 80, 100 and 120 kVp, 0.9, 2.2 and 3.2 pitch values. Quantitative assessment of image quality was determined by measuring signal-to-noise ratio (SNR) in both main pulmonary arteries, while qualitative analysis of images was scored by two experienced radiologists (score of 1 indicates poor visualization of thrombus with no confidence, and score of 5 excellent visualization of thrombus with high confidence) to determine the image quality in relation to different scanning protocols for detection of thrombus in the pulmonary arteries. No significant differences were found in SNR measurements among all CTPA protocols (P>0.05), regardless of kVp or pitch values used, although SNR was higher with 120 kVp and 0.9 and 2.2 pitch protocols than that in other protocols. The thrombi were detected in all images, with 70 kVp and 3.2 pitch protocol scored the lowest with a score of 3 by two observers, and images with other protocols were scored 4 or 5. Lowering kVp from 120 to 70 with use of high-pitch 2.2 or 3.2 protocol resulted in up to 80% dose reduction without significantly affecting image quality. Low-dose CT pulmonary angiography protocols comprising 70 kVp and high pitch 2.2 or 3.2 allow for detection of peripheral PE with significant reduction in radiation dose while images are still considered diagnostic.

CT pulmonary angiography: dose reduction via a next generation iterative reconstruction algorithm.

Computed tomography pulmonary angiography (CTPA) is the standard imaging modality for detection or rule out of pulmonary embolism (PE); however, radiation exposure is a serious concern. With iterative reconstruction algorithms a distinct dose reduction could be achievable. To evaluate a next generation iterative reconstruction algorithm for detection or rule-out of PE in simulated low-dose CTPA. Low-dose CT datasets with 50%, 25%, and 12.5% of the original tube current were simulated based on CTPA examinations of 92 patients with suspected PE. All datasets were reconstructed with two reconstruction algorithms: standard filtered back-projection (FBP) and iterative model reconstruction (IMR). In total, 736 CTPA datasets were evaluated by three blinded radiologists regarding image quality, diagnostic confidence, and detectability of PE. Furthermore, contrast-to-noise ratio (CNR) was calculated. Images reconstructed with IMR showed better detectability of PE than images reconstructed with FBP, especially at lower dose levels. With IMR, sensitivity was over 95% for central and segmental PE down to a dose level of 25%. Significantly higher subjective image quality was shown at lower dose levels (25% and 12.5%) for IMR images whereas it was higher for FBP images at higher dose levels. FBP was rated as showing less artificial image appearance. CNR was significantly higher with IMR at all dose levels. By using IMR, a dose reduction of up to 50% while maintaining satisfactory image quality seems feasible in standard clinical situations, resulting in a mean effective dose of 1.38 mSv for CTPA.

Low-dose CT pulmonary angiography on a 15-year-old CT scanner: a feasibility study.

BackgroundComputed tomography (CT) low-dose (LD) imaging is used to lower radiation exposure, especially in vascular imaging; in current literature, this is mostly on latest generation high-end CT systems.PurposeTo evaluate the effects of reduced tube current on objective and subjective image quality of a 15-year-old 16-slice CT system for pulmonary angiography (CTPA).Material and MethodsCTPA scans from 60 prospectively randomized patients (28 men, 32 women) were examined in this study on a 15-year-old 16-slice CT scanner system. Standard CT (SD) settings were 100 kV and 150 mAs, LD settings were 100 kV and 50 mAs. Attenuation of the pulmonary trunk, various anatomic landmarks, and image noise were quantitatively measured; contrast-to-noise ratios (CNR) and signal-to-noise ratios (SNR) were calculated. Three independent blinded radiologists subjectively rated each image series using a 5-point grading scale.ResultsCT dose index (CTDI) in the LD series was 66.46% lower compared to the SD settings (2.49 ± 0.55 mGy versus 7.42 ± 1.17 mGy). Attenuation of the pulmonary trunk showed similar results for both series (SD 409.55 ± 91.04 HU; LD 380.43 HU ± 93.11 HU; P = 0.768). Subjective image analysis showed no significant differences between SD and LD settings regarding the suitability for detection of central and peripheral PE (central SD/LD, 4.88; intra-class correlation coefficients [ICC], 0.894/4.83; ICC, 0.745; peripheral SD/LD, 4.70; ICC, 0.943/4.57; ICC, 0.919; all P > 0.4).ConclusionThe LD protocol, on a 15-year-old CT scanner system without current high-end hardware or post-processing tools, led to a dose reduction of approximately 67% with similar subjective image quality and delineation of central and peripheral pulmonary arteries.

An audit of patient radiation in low-dose CT pulmonary angiography

ObjectivesAssesment of radiation dose implementing low-dose CTPA protocols. MethodRetrospective analysis of radiation dose in two groups of adult patients, who underwent CECT chest and who were scanned by low-dose CTPA protocol from April 2014 to June 2015. Dose reduction techniques in CTPA included low kVp and iterative reconstruction.The values for CT dose index/volume and the dose-length product (DLP) were available from patients’ information sheet. Effective dose (ED) was calculated by multiplying DLP by body-specific conversion factor, k factor, 0.014.Statistical analysis using SPSS 16 was done for mean DLP, ED as well as paired T-test for comparison of groups. ResultsDLP for CECT chest protocol was 218mGycm. Mean DLP value when applying low-dose CTPA technique was 166.2mGycm. The ED from CECT chest protocol was 1.6–6.3mSv, while using low-dose CTPA protocol it ranged from 1.2 to 4.3mSv.Statistically significant reduction of 23% of mean effective dose was achieved in Group 2. P value is less than 0.01. ConclusionsLow-dose CTPA protocol results in ED values that are significantly lower than CECT chest protocol and within accepted range for international radiation dose of CTPA.

Ultra Low Dose CT Pulmonary Angiography with Iterative Reconstruction.

ObjectiveEvaluation of a new iterative reconstruction algorithm (IMR) for detection/rule-out of pulmonary embolism (PE) in ultra-low dose computed tomography pulmonary angiography (CTPA).MethodsLower dose CT data sets were simulated based on CTPA examinations of 16 patients with pulmonary embolism (PE) with dose levels (DL) of 50%, 25%, 12.5%, 6.3% or 3.1% of the original tube current setting. Original CT data sets and simulated low-dose data sets were reconstructed with three reconstruction algorithms: the standard reconstruction algorithm “filtered back projection” (FBP), the first generation iterative reconstruction algorithm iDose and the next generation iterative reconstruction algorithm “Iterative Model Reconstruction” (IMR). In total, 288 CTPA data sets (16 patients, 6 tube current levels, 3 different algorithms) were evaluated by two blinded radiologists regarding image quality, diagnostic confidence, detectability of PE and contrast-to-noise ratio (CNR).ResultsiDose and IMR showed better detectability of PE than FBP. With IMR, sensitivity for detection of PE was 100% down to a dose level of 12.5%. iDose and IMR showed superiority to FBP regarding all characteristics of subjective (diagnostic confidence in detection of PE, image quality, image noise, artefacts) and objective image quality. The minimum DL providing acceptable diagnostic performance was 12.5% (= 0.45 mSv) for IMR, 25% (= 0.89 mSv) for iDose and 100% (= 3.57 mSv) for FBP. CNR was significantly (p < 0.001) improved by IMR compared to FBP and iDose at all dose levels.ConclusionBy using IMR for detection of PE, dose reduction for CTPA of up to 75% is possible while maintaining full diagnostic confidence. This would result in a mean effective dose of approximately 0.9 mSv for CTPA.

Diagnostic Accuracy of Computed Tomography Pulmonary Angiography With Reduced Radiation and Contrast Material Dose

The objective of the study was to test the diagnostic performance of low-dose computed tomography pulmonary angiography (CTPA) at peak tube voltage of 80 kVp with both reduced radiation and reduced contrast material (CM) dose. In this single-center, single-blinded prospective randomized trial, 501 patients with body weights of less than 100 kg with suspected acute pulmonary embolism (PE) were assigned to normal-dose CTPA (100-kVp tube energy and 100-mL CM, 255 patients) and low-dose CTPA (80-kVp tube energy and 75-mL CM, 246 patients). Primary end points were evidence of PE in CTPA and accuracy of CTPA on a composite reference standard. Results were compared by calculating the odds ratio with the 95% confidence interval. The reference diagnosis was equivocal in 20 of the 501 patients. Diagnosis of CTPA was correct in 240 patients and incorrect in 5 in the normal-dose group. Computed tomography pulmonary angiography was correct in 230 patients and incorrect in 6 in the low-dose group (odds ratio, 1.25; 95% confidence interval, 0.38-4.16; P = 0.77). Sensitivity was 96.9% and 100% and specificity was 98.1% and 97.1% in the normal-dose and low-dose groups, respectively. No PE or PE-related death occurred during the 90-day follow-up. The size-specific dose estimates were 30% lower at 80 kVp (4.8 ± 1.0 mGy) compared with that at 100 kVp (6.8 ± 1.2 mGy; P < 0.001). The accuracy of low-dose CTPA at 80 kVp with a 30% reduced radiation dose and a 25% lower CM volume is not significantly different from that of normal-dose CTPA at 100 kVp in detecting acute PE in patients weighing less than 100 kg.

Impact of Tube Current-Time and Tube Voltage Reduction in 64-Detector-row Computed Tomography Pulmonary Angiography for Pulmonary Embolism in a Porcine Model

To evaluate the impact of dose reduction in multidetector computed tomography pulmonary angiography (CTPA) for detection of pulmonary embolism (PE). After induction of PE in 6 anesthetized pigs, a 64-detector-row CTPA was performed at 3 different dose protocols: A (120 kV/120 mAseff.), B (120 kV/80 mAseff.), and C (80 kV/80 mAseff.). Images were evaluated by 2 radiologists independently. A high-dose CTPA (120 kV/250 mAseff.) served as a reference standard. Sensitivity, specificity, and positive and negative predictive values were calculated and compared using the Wilcoxon test. Interobserver agreement was determined by calculation of κ values. Radiation exposure and objective image parameters were assessed and compared with a 2-sided t test. In the reference scan, a total of 94 emboli were detected: 17 in the main and lobar pulmonary level (category A), 47 in the segmental level (category B), and 30 in the subsegmental level (category C). All protocols reached high diagnostic accuracy in the detection of PE in category A. No significant difference was observed between protocols A and B in the detection rate of segmental and subsegmental PE (sensitivity: 93.6% and 91.5% vs 85.1% and 87.2%; positive predictive value: 100% and 97.7% vs 97.5% and 95.3%). Interobserver agreement was excellent at the segmental (κ=0.97 and 0.94) and subsegmental levels (κ=0.94 and 0.92). Using protocol C, the detection rate of segmental and subsegmental emboli was significantly impaired and interobserver agreement was significantly inferior (sensitivity: 46.8% and 44.6% at segmental and 56.7% and 50.0% at subsegmental level; κ=0.70 and 0.60, respectively; P<0.05). Vessel attenuation was significantly higher in protocol C, [710.3 Hounsfield units (HU) ±200.6 SD] than in protocols A (414.4 HU±82.5 SD) and B (428.8 HU±78.9 SD) (P<0.001). Signal-to-noise and contrast-to-noise ratios were significantly decreased in protocols B (55.6; 45.8) and C (44.3; 39.4) compared with protocol A (62.1; 52.3) (P<0.05). Radiation dose was significantly reduced between protocols A and B and protocols B and C [volume CT dose index (CTDIvol): 7.1 vs 4.7 vs 1.4 mGy; dose-length product: 199.5 vs 132.1 vs 39.4 mGy·cm and E: 3.39 vs 2.25 vs 0.6 mSv; P<0.05]. This animal study proves the diagnostic use of a low-dose CTPA protocol with 80 mAseff. at 120 kV for PE evaluation without significant loss of diagnostic accuracy compared with a standard protocol with 120 mAseff. Using an "ultra-low"-dose CTPA protocol (80 kV; 80 mAseff.), emboli detection at the segmental and subsegmental level is significantly impaired, whereas evaluation of central emboli is still feasible with high diagnostic accuracy.

Low-dose pulmonary CT angiography: reduced radiation exposure and iodine load at low tube kilovoltage

CT pulmonary angiography is the currently accepted standard in ruling out acute pulmonary embolism. Issues of radiation dose received by patients via CT have been extensively disputed by radiologists and reported by the media. In recent years there has been considerable research performed to find ways for reducing radiation exposure from CT. Herein, we will discuss specific measures that have been shown to be valuable for CT pulmonary angiography. The limitations and the potential benefits of reduced CT peak tube kilovoltage will be detailed as this method is capable of reducing both radiation exposure and iodine load to the patient simultaneously. We discuss some of the emerging tools, which will hopefully play a significant role in wider acceptance of low-dose CT pulmonary angiography protocols.