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

Estimation of maternal and foetal risk of radiation-induced cancer from a survey of computed tomography pulmonary angiography and ventilation/perfusion lung scanning for diagnosing pulmonary embolism during pregnancy

INTRODUCTION

While there are many papers on maternal and foetal radiation doses from computed tomography pulmonary angiography (CTPA) and ventilation/perfusion (V/Q) lung scanning examinations for diagnosing pulmonary embolism in pregnant patients, few have used clinical data to examine the patient lifetime attributable risk (LAR) of different cancer types. This paper aims to estimate the cancer risk from maternal radiation doses from CTPA and V/Q examinations and associated foetal doses.

METHODS

Dosimetric data were determined for 267 pregnant patients who received CTPA and/or V/Q examinations over 8 years. Organ and foetal doses were determined using software allowing patient size variations for CTPA and using two different activity-to-organ dose conversion methods for V/Q scans. The LAR of cancer incidence was estimated using International Commission on Radiological Protection (ICRP) modelling including estimates of detriment.

RESULTS

Estimated total cancer incidence was 23 and 22 cases per 100,000 for CTPA and V/Q examinations, respectively, with detriment estimates of 18 and 20 cases. Cancer incidence was evenly divided between lung and breast cancer for CTPA with lung cancer being 80% of all cancer for V/Q. The median foetal doses were 0.03 mSv for CTPA and 0.29 mSv for V/Q. Significant differences in estimated foetal dose for V/Q scans were obtained by the two different methods used. The differences in dose between the modes of CTPA scan acquisition highlight the importance of optimisation.

CONCLUSION

Maternal cancer incidence and detriment were remarkably similar for each examination. Optimisation of examinations is critical for low-dose outcomes, particularly for CTPA examination.

Feasibility of Low-Dose and Low-Contrast Media Volume Approach in Computed Tomography Cardiovascular Imaging Reconstructed with Model-Based Algorithm

Aim: To evaluate the dose reduction and image quality of low-dose, low-contrast media volume in computed tomography (CT) examinations reconstructed with the model-based iterative reconstruction (MBIR) algorithm in comparison with the hybrid iterative (HIR) one. Methods: We prospectively enrolled a total of 401 patients referred for cardiovascular CT, evaluated with a 256-MDCT scan with a low kVp (80 kVp) reconstructed with an MBIR (study group) or a standard HIR protocol (100 kVp-control group) after injection of a fixed dose of contrast medium volume. Vessel contrast enhancement and image noise were measured by placing the region of interest (ROI) in the left ventricle, ascending aorta; left, right and circumflex coronary arteries; main, right and left pulmonary arteries; aortic arch; and abdominal aorta. The signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were computed. Subjective image quality obtained by consensus was assessed by using a 4-point Likert scale. Radiation dose exposure was recorded. Results: HU values of the proximal tract of all coronary arteries; main, right and left pulmonary arteries; and of the aorta were significantly higher in the study group than in the control group (p < 0.05), while the noise was significantly lower (p < 0.05). SNR and CNR values in all anatomic districts were significantly higher in the study group (p < 0.05). MBIR subjective image quality was significantly higher than HIR in CCTA and CTPA protocols (p < 0.05). Radiation dose was significantly lower in the study group (p < 0.05). Conclusions: The MBIR algorithm combined with low-kVp can help reduce radiation dose exposure, reduce noise, and increase objective and subjective image quality.

A closer look at the utilized radiation doses during computed tomography pulmonary angiography (CTPA) for COVID-19 patients

Introduction

CTPA stands for computed tomography pulmonary angiography. CTPA is an X-ray imaging that combines X-rays and computer technology to create detailed images of the pulmonary arteries and veins in the lungs. This test diagnoses and monitors conditions like pulmonary embolism, arterial blockages, and hypertension. Coronavirus (COVID-19) has threatened world health over the last three years. The number of (CT) scans increased and played a vital role in diagnosing COVID-19 patients, including life-threatening pulmonary embolism (PE). This study aimed to assess the radiation dose resulted from CTPA for COVID-19 patients.

Methods

Data were collected retrospectively from CTPA examinations on a single scanner in 84 symptomatic patients. The data collected included the dose length product (DLP), volumetric computed tomography dose index (CTDIvol), and size-specific dose estimate (SSDE). The organ dose and effective dose were estimated using VirtualDose software.

Results

The study population included 84 patients, 52% male and 48% female, with an average age of 62. The average DLP, CTDIvol, and SSDE were 404.2 mGy cm, 13.5 mGy, and 11.6 mGy\, respectively. The mean effective doses (mSv) for males and females were 3.01 and 3.29, respectively. The maximum to minimum organ doses (mGy) between patients was 0.8 for the male bladder and 7.33 for the female lung.

Conclusions

The increase in CT scans during the COVID-19 pandemic required close dose monitoring and optimization. The protocol used during CTPA should guarantee a minimum radiation dose with maximum patient benefits.

Low dose CTPA using a low kV technique combined with high IR: A clinical study

INTRODUCTION

To investigate optimising a computerised tomography pulmonary angiogram (CTPA) scan protocol in terms of radiation dose and image quality using a low kV technique combined with high iterative reconstruction (IR) parameters (>50%) and apply the optimised protocol in clinical practice on patients irrespective of their body weight.

METHODS

CTPA examinations were performed on 64 patients equally divided into control and experimental groups. Patients in the control group were scanned using the current protocol (100 kV with 50% IR) while patients in the experimental group were scanned using an optimised protocol (80 kV with 60%IR). The radiation dose indices volume computerised tomography dose index (CTDIvol), dose length product (DLP), size specific dose estimates (SSDE) and effective dose (ED) were recorded. Subjective image quality was evaluated by 3 radiologists through absolute visual grading analysis (VGA) using an image quality scoring tool. The resultant image quality scores were analysed using Visual Grading Characteristics (VGC). Objective image quality was recorded in terms of contrast-to-noise-ratio (CNR) and signal-to-noise-ratio (SNR).

RESULTS

The application of the optimised protocol resulted in a statistically significant (p < 0.05) reduction in mean CTDIvol (-49%), DLP (-48%), SSDE (-52%) and ED (-49%). Objective image quality was significantly (p < 0.05) improved both in CNR (32%) and SNR (13%). Subjective image quality scores were higher for the current protocol but variation between the two protocols was not significant (p = 0.650).

CONCLUSIONS

When applying the low kV technique combined with high IR parameters, a significant dose reduction may be achieved while still maintaining diagnostic image quality.

IMPLICATIONS FOR PRACTICE

The low kV technique combined with high IR parameters is an effective optimisation technique which can be easily implemented for the CTPA protocol.

Optimisation of the CT pulmonary angiogram (CTPA) protocol using a low kV technique combined with high iterative reconstruction (IR): A phantom study

INTRODUCTION

This study aims to optimise the current CTPA protocol at a public general hospital in Malta using lower kV combined with high Iterative Reconstruction (IR) (>50%).

METHODS

The research consisted of a 2-phase anthropomorphic phantom study. Phase 1: radiation dose evaluation of 6 experimental protocols consisting of the low kV technique and high IR values and comparison with the current protocol. Phase 2: image evaluation. Objective image quality was evaluated in terms of contrast to noise ratio (CNR) and signal to noise ratio (SNR). Subjective image quality evaluation was performed by 3 radiologists undertaking Absolute Visual Grading Analysis (VGA). Resultant image quality scores were analysed using Visual Grading Characteristics (VGC).

RESULTS

All experimental protocols achieved significant (p < 0.05) dose reductions. SNR and CNR improved in almost all protocols, however, differences were not significant (p > 0.05). In subjective image quality analysis, the current protocol provided significant superior image quality (AUC > 0.5; p < 0.05) when compared to the experimental protocols consisting of 80 kV with 70%, 80%, 90% and 100% IR. The only two experimental protocols yielding comparable image quality to the current protocol were 80 kV with 50% IR (AUC: 0.195; p: 0.137) and 80 kV with 60% IR (AUC: 0.554; p: 0.624). The protocol yielding the greatest decrease in radiation dose being 80 kV with 60% IR.

CONCLUSIONS

The optimal IR value was 60%. When applying the optimal experimental protocol (80 kV combined with 60% IR), a significant dose reduction was achieved while maintaining diagnostic image quality.

IMPLICATIONS FOR PRACTICE

The low kV technique combined with high IR parameter is easily implemented and involves no additional cost and equipment.

Presentation, Management and Outcomes of Pediatric Pulmonary Embolus: A Retrospective Review

OBJECTIVES

To review the presentation, management, and outcomes of pediatric pulmonary embolism (PE) patients treated at a single institution over 10 years to determine whether laboratory findings and clinical presentation predict disease severity.

METHODS

We performed a retrospective chart review of patients treated for PE in a 14-bed pediatric intensive care unit from January 1, 2008, to December 31, 2018. Associations between clot burden and disease severity, clinical risk factors (body mass index, recent hospitalization, estrogen use), clinical presentation (heart rate, oxygen saturation), and laboratory values (white blood cell count, D-Dimer, troponin, proBNP) were performed using Student t test, χ2 tests, and 1-way analysis of variance. Patients were risk stratified by American Heart Association guidelines.

RESULTS

Eighteen (72%) patients (girls) were treated for PE. Common risk factors included recent hospitalization (67%) and oral contraceptives (62%). Risk factors, clinical presentation (including hypoxemia and tachypnea), and laboratory studies did not correlate with disease severity or clot burden. Electrocardiogram and radiographic findings were non-specific. Computer tomography pulmonary angiography (CTPA) was required to diagnose 94%. Sixteen received unfractionated heparin, and 5 required additional intervention. Risk factors, clinical features, and laboratory studies did not predict who required intervention.

CONCLUSIONS

Of 18 pediatric patients treated for PE at a single institution over 10 years, vital signs and laboratory data did not predict disease severity or clot burden, and CTPA was required for diagnosis in all but 1. Emergency room providers must have a high index of suspicion for diagnosis and cannot be reassured by normal electrocardiogram or plain film findings. At a time when pediatric providers are under pressure to minimize unnecessary radiation exposure, this lack of correlation of clinical presentation and laboratory findings highlights the importance of considering CTPA when PE is suspected.

Quantifying image quality in chest computed tomography angiography: Evaluation of different contrast-to-noise ratio measurement methods

BACKGROUND

Contrast-to-noise ratio is used to objectively evaluate image quality in chest computed tomography angiography (CTA). Different authors define and measure contrast-to-noise ratio using different methods.

PURPOSE

To summarize and evaluate the different contrast-to-noise ratio calculation formulas in the current literature.

MATERIAL AND METHODS

A systematic review of the recent literature for studies using contrast-to-noise ratio was performed. Contrast-to-noise ratio measurement methods reported by the different authors were recorded and reproduced in three patients who underwent chest CTA in our department for exploring variations among the different measurement methods.

RESULTS

The search resulted in 109 articles, of which 26 were included. The studies involved 69 different measurements and overall, three different formula patterns. In all three, aorta and pulmonary arteries comprised the objects of interest in the numerator. In the denominator, standard deviation of the attenuation of the object of interest itself or of another background were used to reflect image noise. Some authors averaged the ratio values at different levels to obtain global ratio values. Using the object of interest itself for image noise calculation in the denominator compared to the usage of another background caused the most prominent variances of contrast-to-noise ratio between the two different protocols used for the reproduction of the measurements.

CONCLUSION

We recommend using the standard deviation of the attenuation of a background indicator as image noise rather than the object of interest itself for more reliable and comparative values. Global contrast-to-noise ratios based on averaging the values of different measurement levels should be avoided.

Split-bolus computed tomography urography (CTU) achieves more than half of radiation dose reduction in females and overweight patients than conventional single-bolus computed tomography urography

OBJECTIVE

To compare radiation dose between single-bolus and split-bolus computed tomography urography (CTU).

MATERIALS AND METHODS

We prospectively enrolled patients undergoing single-bolus and split-bolus CTU from 2019 June to 2020 June. The age, sex and body mass index (BMI) of each patient was recorded and categorized into BMI classes. The radiation dose indices including volumetric computed dose index, size-specific dose estimate, dose length product and effective dose of each patient were compared between 2 CTU groups with calculation of dose reduction proportions (DRPs).

RESULTS

Seventy-six patients underwent single-bolus (n = 39) and split-bolus (n = 37) CTU. Single-bolus CTU had higher radiation doses than split-bolus CTU and there were statistically significant differences of all radiation dose indices between two CTU groups without and with stratification by sex and BMI classes. The DRPs of volumetric computed dose index, size-specific dose estimate, dose length product and effective dose using split-bolus CTU were 49%, 49%. 50%, and 45%, respectively. Multiple linear regression with an effect size (f2) as 2.24 showed females (p = 0.027) and higher BMI classes (p = 2.38 *10-9) were associated with higher effective doses; and split-bolus CTU, lower effective doses (p = 5.40 *10-15). Using split-bolus CTU, females had consistently higher DRP of all radiation dose indices than males (54-55% versus 40-42%). Overweight patients had the largest DRP as 55% of effective dose.

CONCLUSIONS

Split-bolus CTU could be preferred by its significant radiation dose reduction effect in regard to single-bolus CTU, which was most profound in females and overweight patients.

Optimizing the diagnosis and assessment of chronic thromboembolic pulmonary hypertension with advancing imaging modalities

Imaging is key to nearly all aspects of chronic thromboembolic pulmonary hypertension including management for screening, assessing eligibility for pulmonary endarterectomy, and post-operative follow-up. While ventilation/perfusion scintigraphy, the gold standard technique for chronic thromboembolic pulmonary hypertension screening, can have excellent sensitivity, it can be confounded by other etiologies of pulmonary malperfusion, and does not provide structural information to guide operability assessment. Conventional computed tomography pulmonary angiography has high specificity, though findings of chronic thromboembolic pulmonary hypertension can be visually subtle and unrecognized. In addition, computed tomography pulmonary angiography can provide morphologic information to aid in pre-operative workup and assessment of other structural abnormalities. Advances in computed tomography imaging techniques, including dual-energy computed tomography and spectral-detector computed tomography, allow for improved sensitivity and specificity in detecting chronic thromboembolic pulmonary hypertension, comparable to that of ventilation/perfusion scans. Furthermore, these advanced computed tomography techniques, compared with conventional computed tomography, provide additional physiologic data from perfused blood volume maps and improved resolution to better visualize distal chronic thromboembolic pulmonary hypertension, an important consideration for balloon pulmonary angioplasty for inoperable patients. Electrocardiogram-synchronized techniques in electrocardiogram-gated computed tomography can also show further information regarding right ventricular function and structure. While the standard of care in the workup of chronic thromboembolic pulmonary hypertension includes a ventilation/perfusion scan, computed tomography pulmonary angiography, direct catheter angiography, echocardiogram, and coronary angiogram, in the future an electrocardiogram-gated dual-energy computed tomography angiography scan may enable a "one-stop" imaging study to guide diagnosis, operability assessment, and treatment decisions with less radiation exposure and cost than traditional chronic thromboembolic pulmonary hypertension imaging modalities.

Factors Affecting Radiation Dose in Computed Tomography Angiograms for Pulmonary Embolism: A Retrospective Cohort Study

Objectives

Computed tomography pulmonary angiogram (CTPA) is one of the most commonly ordered and frequently overused tests. The purpose of this study was to evaluate the mean radiation dose to patients getting CTPA and to identify factors that are associated with higher dose.

Material and Methods

This institutionally approved retrospective study included all patients who had a CTPA to rule out acute pulmonary embolism between 2016 and 2018 in a tertiary care center. Patient data (age, sex, body mass index [BMI], and patient location), CT scanner type, image reconstruction methodology, and radiation dose parameters (dose-length product [DLP]) were recorded. Effective dose estimates were obtained by multiplying DLP by conversion coefficient (0.014 mSv•mGy^-1•cm^-1). Multivariate logistic regression analysis was performed to determine the factors affecting the radiation dose.

Results

There were 2342 patients (1099 men and 1243 women) with a mean age of 58.1 years (range 0.2-104.4 years) and BMI of 31.3 kg/m² (range 12-91.5 kg/m²). The mean effective radiation dose was 5.512 mSv (median - 4.27 mSv; range 0.1-43.0 mSv). Patient factors, including BMI >25 kg/m², male sex, age >18 years, and intensive care unit (ICU) location, were associated with significantly higher dose (P < 0.05). CT scanning using third generation dual-source scanner with model-based iterative reconstruction (IR) had significantly lower dose (mean: 4.90 mSv) versus single-source (64-slice) scanner with filtered back projection (mean: 9.29 mSv, P < 0.001).

Conclusion

Patients with high BMI and ICU referrals are associated with high CT radiation dose. They are most likely to benefit by scanning on newer generation scanner using advance model-based IR techniques.

Evaluation of Image Quality for 7 Iterative Reconstruction Algorithms in Chest Computed Tomography Imaging: A Phantom Study

OBJECTIVES

This study aimed to evaluate the image quality of 7 iterative reconstruction (IR) algorithms in comparison to filtered back-projection (FBP) algorithm.

METHODS

An anthropomorphic chest phantom was scanned on 4 computed tomography scanners and reconstructed with FBP and IR algorithms. Image quality of anatomical details-large/medium-sized pulmonary vessels, small pulmonary vessels, thoracic wall, and small and large lesions-was scored. Furthermore, general impression of noise, image contrast, and artifacts were evaluated. Visual grading regression was used to analyze the data. Standard deviations were measured, and the noise power spectrum was calculated.

RESULTS

Iterative reconstruction algorithms showed significantly better results when compared with FBP for these criteria (regression coefficients/P values in parentheses): vessels (FIRST: -1.8/0.05, AIDR Enhanced: <-2.3/0.01, Veo: <-0.1/0.03, ADMIRE: <-2.1/0.04), lesions (FIRST: <-2.6/0.01, AIDR Enhanced: <-1.9/0.03, IMR1: <-2.7/0.01, Veo: <-2.4/0.02, ADMIRE: -2.3/0.02), image noise (FIRST: <-3.2/0.004, AIDR Enhanced: <-3.5/0.002, IMR1: <-6.1/0.001, iDose: <-2.3/0.02, Veo: <-3.4/0.002, ADMIRE: <-3.5/0.02), image contrast (FIRST: -2.3/0.01, AIDR Enhanced: -2.5/0.01, IMR1: -3.7/0.001, iDose: -2.1/0.02), and artifacts (FIRST: <-3.8/0.004, AIDR Enhanced: <-2.7/0.02, IMR1: <-2.6/0.02, iDose: -2.1/0.04, Veo: -2.6/0.02). The iDose algorithm was the only IR algorithm that maintained the noise frequencies.

CONCLUSIONS

Iterative reconstruction algorithms performed differently on all evaluated criteria, showing the importance of careful implementation of algorithms for diagnostic purposes.

Association of Radiation Doses and Cancer Risks from CT Pulmonary Angiography Examinations in Relation to Body Diameter

In this study, we aimed to estimate the probability of cancer risk induced by CT pulmonary angiography (CTPA) examinations concerning effective body diameter. One hundred patients who underwent CTPA examinations were recruited as subjects from a single institution in Kuala Lumpur. Subjects were categorized based on their effective diameter size, where 19–25, 25–28, and >28 cm categorized as Groups 1, 2, and 3, respectively. The mean value of the body diameter of the subjects was 26.82 ± 3.12 cm, with no significant differences found between male and female subjects. The risk of cancer in breast, lung, and liver organs was 0.009%, 0.007%, and 0.005% respectively. The volume-weighted CT dose index (CTDI_vol) was underestimated, whereas the size-specific dose estimates (SSDEs) provided a more accurate description of the radiation dose and the risk of cancer. CTPA examinations are considered safe but it is essential to implement a protocol optimized following the As Low as Reasonably Achievable (ALARA) principle.

Acute pulmonary embolism multimodality imaging prior to endovascular therapy

The manuscript discusses the application of CT pulmonary angiography, ventilation–perfusion scan, and magnetic resonance angiography to detect acute pulmonary embolism and to plan endovascular therapy. CT pulmonary angiography offers high accuracy, speed of acquisition, and widespread availability when applied to acute pulmonary embolism detection. This imaging modality also aids the planning of endovascular therapy by visualizing the number and distribution of emboli, determining ideal intra-procedural catheter position for treatment, and signs of right heart strain. Ventilation–perfusion scan and magnetic resonance angiography with and without contrast enhancement can also aid in the detection and pre-procedural planning of endovascular therapy in patients who are not candidates for CT pulmonary angiography.

Effect of iterative reconstruction algorithm levels on noise index and figure-of-merit in CT pulmonary angiography examinations

PURPOSE

To evaluate the influence of iterative reconstruction (IR) levels on Computed Tomography (CT) image quality and to establish Figure of Merit (FOM) value for CT Pulmonary Angiography (CTPA) examinations.

METHODS

Images of 31 adult patients who underwent CTPA examinations in our institution from March to April 2019 were retrospectively collected. Other data, such as scanning parameters, radiation dose and body habitus information from the subjects were also recorded. Six different levels of IR were applied to the volume data of the subjects. Five circles of the region of interest (ROI) were drawn in five different arteries namely, pulmonary trunk, right pulmonary artery, left pulmonary artery, ascending aorta and descending aorta. The mean Signal-to-noise ratio (SNR) was obtained, and the FOM was calculated in a fraction of the SNR2 divided by volume-weighted CT dose index (CTDIvol) and SNR2 divided by the size-specific dose estimates (SSDE).

RESULTS

Overall, we observed that the mean value of CTDIvol and SSDE were 13.79±7.72 mGy and 17.25±8.92 mGy, respectively. Notably, SNR values significantly increase with increase of the IR level (p < 0.05). There are also significant differences (p < 0.05) in the FOM for both SNR2/SSDE and SNR2/CTDIvol attained in different IR levels.

CONCLUSION

We successfully evaluate the value of radiation dose and image quality performance and set up a figure of merit for both parameters to further verify scanning protocols by radiology personnel.

Ultralow-dose CT with knowledge-based iterative model reconstruction (IMR) in evaluation of pulmonary tuberculosis: comparison of radiation dose and image quality

OBJECTIVES

To evaluate the image quality of ultralow-dose computed tomography (ULDCT) reconstructed with knowledge-based iterative model reconstruction (IMR) in patients with pulmonary tuberculosis (TB).

METHODS

This IRB-approved prospective study enrolled 59 consecutive patients (mean age, 43.9 ± 16.6 years; F:M 18:41) with known or suspected pulmonary TB. Patients underwent a low-dose CT (LDCT) using automatic tube current modulation followed by an ULDCT using fixed tube current. Raw image data were reconstructed with filtered-back projection (FBP), hybrid iterative reconstruction (iDose), and IMR. Objective measurements including CT attenuation, image noise, and contrast-to-noise ratio (CNR) were assessed and compared using repeated-measures analysis of variance. Overall image quality and visualization of normal and pathological findings were subjectively scored on a five-point scale. Radiation output and subjective scores were compared by the paired Student t test and Wilcoxon signed-rank test, respectively.

RESULTS

Compared with FBP and iDose, IMR yielded significantly lower noise and higher CNR values at both dose levels (p < 0.01). Subjective ratings for pathological findings including centrilobular nodules, consolidation, tree-in-bud, and cavity were significantly better with ULDCT IMR images than those with LDCT iDose images (p < 0.01), but blurred edges were observed. With IMR implementation, a 59% reduction of the mean effective dose was achieved with ULDCT (0.28 ± 0.02 mSv) compared with LDCT (0.69 ± 0.15 mSv) without impairing image quality (p < 0.001).

CONCLUSIONS

IMR offers considerable noise reduction and improvement in image quality for patients with pulmonary TB undergoing chest ULDCT at an effective dose of 0.28 mSv.

KEY POINTS

• Radiation dose is a major concern for tuberculosis patients requiring repeated follow-up CT. • IMR allows substantial radiation dose reduction in chest CT without compromising image quality. • ULDCT reconstructed with IMR allows accurate depiction of CT features of pulmonary tuberculosis.