Detailed distribution of acute pulmonary thromboemboli: Direct evidence for reduction of acquisition length and radiation dose for triple rule-out CT angiography

Diagnosing Pulmonary Embolism With Computed Tomography Pulmonary Angiography: Diagnostic Accuracy of a Reduced Scan Range

PURPOSE

Computed tomography pulmonary angiography (CT-PA) is frequently used in the diagnostic workup of pulmonary embolism (PE), even in highly radiosensitive patient populations. This study aims to assess CT-PA with reduced z -axis coverage (compared with a standard scan range covering the entire lung) for its sensitivity for detecting PE and its potential to reduce the radiation dose.

MATERIALS AND METHODS

We retrospectively analyzed 602 consecutive CT-PA scans with definite or possible PE reported. A reduced scan range was defined based on the topogram, where the cranial slice was set at the top of the aortic arch and the caudal slice at the top of the lower hemidiaphragm. Locations of emboli in relation to the reduced scan range were recorded.

RESULTS

We included 513 CT-PA scans with definite acute PE in statistical analysis. Patients' median age was 66 (52 to 77) years, 46% were female. Median dose length product was 270.8 (111.3 to 503.9) mGy*cm. Comparing the original and reduced scan ranges, the mean scan length was significantly reduced by 48.0±8.6% (26.8±3.0 vs. 13.9±2.6 cm, P <0.001). Single emboli outside the reduced range in addition to emboli within were found in 15 scans (2.9%), while only 1 scan (0.2%) had an embolus outside the reduced range and none within it. The resulting sensitivity of CT-PA with reduced scan range was 99.81% (95% confidence interval: 98.74%-99.99%) for detecting any PE.

CONCLUSION

A reduced scan length in CT-PA, as defined above, would substantially decrease radiation dose while maintaining diagnostic accuracy for detecting PE.

The Effect of Limiting the Scan Range of Computed Tomography Pulmonary Angiography (to Reduce Radiation Exposure) on the Detection of Pulmonary Embolism: A Systematic Review

(1) Background: Computed tomography pulmonary angiography (CTPA) is the standard imaging test for the evaluation of acute pulmonary embolism (PE), but it is associated with patients' exposure to radiation. Studies have suggested that radiation exposure can be reduced without compromising PE detection by limiting the scan range (the z-axis, going from up to down); (2) Methods: A literature search was conducted in MEDLINE and EMBASE on 17 July 2021. Studies were included if they enrolled patients who had undergone a CTPA and described the yield of PE diagnoses, number of missed filling defects and/or other diagnoses using a reduced z-axis in comparison to a full-length scan. To assess risk of bias, we modified an existing risk of bias tools for observational studies, the Newcastle-Ottawa Scale. Results were synthesized in a narrative review. Primary outcomes were the number of missed PE diagnoses (based on at least one filling defect) and filling defects; the secondary outcome was the number of other missed findings; (3) Results: Eleven cohort studies and one case-control study were included reporting on a total of 3955 scans including 1025 scans with a diagnosis of PE. Six different reduced scan ranges were assessed; the most studied was from the top of the aortic arch to below the heart, in which no PEs were missed (seven studies). One sub-segmental PE was missed when the scan coverage was 10 cm starting from the bottom of the aortic arch and 14.7 cm starting from the top of the arch. Five studies that reported on other findings all found that other diagnoses were missed with a reduced z-axis. Most of the included studies had a high risk of bias; (4) Conclusions: CTPA scan coverage reduction from the top of aortic arch to below the heart reduced radiation exposure without affecting PE diagnoses, but studies were generally at high risk of bias.

Variability of redundant scan coverages along the Z-axis and dose implications for common computed tomography examinations

BACKGROUND

Scan length optimization is a method of optimization which ensures that, imaging is performed to cover just the area of interest without unnecessarily exposing structures that would not add value to answer a given clinical question.

PURPOSE

This study assessed the variability and degree of redundant scan coverages along the z-axis of CT examinations of common indications and the associated radiation dose implications in CT facilities in Ghana for optimization measures to be recommended.

METHODS

On reconstructed acquired CT images, the study measured extra distances covered above and below anatomical targets for common indications with calibrated calipers across 25 CT facilities. The National Cancer Institute Dosimetry System for CT (NCICT) (Monte Carlo-based-software) was used to simulate the scanning situations and organ dose implications for scans with and without the inclusion of the redundant scan areas.

RESULTS

A total of 1,640 patients' CT data sets were used in this study. The results demonstrated that CT imaging utilized varying scan lengths (16.45±21.0-45.99±4.3 cm), and 70.6% of the scans exceeded their pre-defined anatomic boundaries by a mean range of 2.86±1.07-5.81±1.66 cm, thereby resulting in extra patient radiation dose. Hence, scanning without the redundant coverages could generate a dose length product (DLP) reduction of 17.5%, 18.8%, 15.5% and 9.0% without degrading image quality for brain lesion, lung lesion, pulmonary embolism and abdominopelvic lesion CT imaging, respectively, whilst ensuring organ dose reduction of0.8%-79.1%.

CONCLUSION

The study strongly recommends that radiographers should avoid the inclusion of redundant areas in CT examinations to reduce organ doses.

Diagnostic Performance of a Contrast-Enhanced Ultra-Low-Dose High-Pitch CT Protocol with Reduced Scan Range for Detection of Pulmonary Embolisms

(1) Background: To evaluate the diagnostic performance of a simulated ultra-low-dose (ULD), high-pitch computed tomography pulmonary angiography (CTPA) protocol with low tube current (mAs) and reduced scan range for detection of pulmonary embolisms (PE). (2) Methods: We retrospectively included 130 consecutive patients (64 ± 16 years, 69 female) who underwent clinically indicated high-pitch CTPA examination for suspected acute PE on a 3rd generation dual-source CT scanner (SOMATOM FORCE, Siemens Healthineers, Forchheim, Germany). ULD datasets with a realistic simulation of 25% mAs, reduced scan range (aortic arch-basal pericardium), and Advanced Modeled Iterative Reconstruction (ADMIRE®, Siemens Healthineers, Forchheim, Germany) strength 5 were created. The effective radiation dose (ED) of both datasets (standard and ULD) was estimated using a dedicated dosimetry software solution. Subjective image quality and diagnostic confidence were evaluated independently by three reviewers using a 5-point Likert scale. Objective image quality was compared using noise measurements. For assessment of diagnostic accuracy, patients and pulmonary vessels were reviewed binarily for affection by PE, using standard CTPA protocol datasets as the reference standard. Percentual affection of pulmonary vessels by PE was computed for disease severity (modified Qanadli score). (3) Results: Mean ED in ULD protocol was 0.7 ± 0.3 mSv (16% of standard protocol: 4.3 ± 1.7 mSv, p < 0.001, r > 0.5). Comparing ULD to standard protocol, subjective image quality and diagnostic confidence were comparably good (p = 0.486, r > 0.5) and image noise was significantly lower in ULD (p < 0.001, r > 0.5). A total of 42 patients (32.2%) were affected by PE. ULD protocol had a segment-based false-negative rate of only 0.1%. Sensitivity for detection of any PE was 98.9% (95% CI, 97.2-99.7%), specificity was 100% (95% CI, 99.8-100%), and overall accuracy was 99.9% (95% CI, 98.6-100%). Diagnoses correlated strongly between ULD and standard protocol (Chi-square (1) = 42, p < 0.001) with a decrease in disease severity of only 0.48% (T = 1.667, p = 0.103). (4) Conclusions: Compared to a standard CTPA protocol, the proposed ULD protocol proved reliable in detecting and ruling out acute PE with good levels of image quality and diagnostic confidence, as well as significantly lower image noise, at 0.7 ± 0.3 mSv (84% dose reduction).

Reduced z-axis coverage in multidetector-row CT pulmonary angiography decreases radiation dose and diagnostic accuracy of alternative diseases

OBJECTIVE

To investigate the effect of a two-third reduction of the scanned length (i.e. 10 cm) on diagnosis of both pulmonary embolism (PE) and alternative diseases.

METHODS

247 consecutive patients suspected of acute PE had a CT pulmonary angiography (CTPA) of the thorax (standard length, L). Based on this acquisition, a second set of images was created to obtain a scan length of 10 cm caudally to the aortic arch (l). Images were anonymized, randomized and interpreted by two independent readers. The quality of enhancement, the presence of PE and the possible alternative and/or complementary diagnoses were recorded. A McNemar exact test investigated differences in discrepancies between readers and between scan lengths.

RESULTS

57 (23%) patients had an acute PE. Among l sets, PE was missed by both readers in one (1.8%) patient, because the unique clot was localized in a subsegmental artery out of the 10-cm range. There were discrepancies between L and l sets in 9 (3.6%) and 11 (4.5%) patients, by Readers 1 and 2 (p=0.820), respectively. Discrepancies between the readers of L sets and those between both sets were not different regardless of the reader (p>0.99). There were discrepancies between both sets for alternative and/or complementary diagnoses in 43 (17.2%) patients.

CONCLUSION

Although its performance in diagnosing PE is maintained, CTPA should not be restricted to a range of 10 cm centred over the pulmonary hilum, because alternative and/or complementary diagnoses could be missed.

ADVANCES IN KNOWLEDGE

(1) A 10-cm CTPA acquisition reduces the radiation dose by two-thirds as compared with a standard one, but does not impair the accuracy for the diagnosis of PE. (2) Significant alternative diagnoses are missed in 17.2% of patients when reducing the acquisition height to 10 cm.

Diagnostic value of nonenhanced multidetector computed tomography for ruling out acute aortic dissection in patients presenting with chest or back pain

BACKGROUND

Multidetector computed tomography (MDCT) is widely used for diagnosing acute aortic dissection (AAD). However, the diagnostic value of nonenhanced MDCT for AAD remains unknown. We evaluated the usefulness of nonenhanced 64-slice MDCT for ruling out AAD in patients presenting with chest or back pain.

METHODS

Of 107 patients with clinical suspicion of AAD who underwent MDCT, AAD was confirmed in 47 and ruled out in 60. Nonenhanced MDCT data of all patients were retrospectively assessed by 2 independent observers unaware of clinical information and contrast-enhanced MDCT data. The diagnostic performance of nonenhanced MDCT parameters to detect AAD was calculated.

RESULTS AND CONCLUSION

Among the parameters, positive intimal flap, defined as the clear presence of a high-density membrane-like structure in the aorta on serial axial images, had a sensitivity of 87%, a specificity of 100%, a positive predictive value (PPV) of 100%, and a negative predictive value (NPV) of 91%, respectively. The addition of equivocal intimal flap, defined as the ambiguous presence of a high-density membrane-like structure in the aorta on at least one axial image, increased both the sensitivity and NPV to 96%. Furthermore, the combination of intimal flap (positive+equivocal or positive alone) and high-density area in the aorta showed the highest sensitivity (98%) and NPV (98%). Combination of the nonenhanced MDCT parameters intimal flap and high-density area in the aorta provides excellent sensitivity and NPV, suggesting that nonenhanced MDCT is an effective modality for ruling out AAD in patients with chest or back pain.

Personalized assessment of radiation risks from the one-stop-shop myocardial 256-slice CT examination

BACKGROUND

This study provides data on the cumulative life attributable risk (LAR) of radiation-induced cancer from the combination of coronary CT angiography (CCTA), dynamic CT perfusion (CTP) and delayed enhancement (DE) CT scans, required for reliable risk-benefit analysis of the one-stop-shop CCTA + CTP + DECT cardiac examination.

METHODS

Monte Carlo simulation of the dynamic CTP and DECT exposures on 62 adult individuals was employed to determine radiation absorbed dose to exposed radiosensitive organs. Corresponding data for CCTA were derived using patient chest circumference and previously published data. Individual-specific LARs of cancer were estimated using organ/tissue-specific radiogenic cancer risk factors. Total LAR from CCTA + CTP + DECT scans' sequence were estimated and compared to nominal intrinsic risk of cancer.

RESULTS

The main contribution, up to 80%, to cumulative radiation burden from CCTA + CTP + DECT scan-sequence was found to originate from the CTP scan. The total LAR from CCTA + CTP + DECT for females was found 4-6 times higher, compared to males. The mean cumulative risk of radiogenic cancer associated with the complete CCTA + CTP + DECT scan sequence was found to marginally increase the intrinsic risk for cancer induction by less than 0.6% and 0.1% for females and males, respectively.

CONCLUSIONS

The radiation risk from the 256-slice CCTA + CTP + DECT scan sequence may be considered low and should not constitute an obstacle for the clinical endorsement of the one-stop-shop cardiac CT examination, given that its clinical value has been well verified. Nevertheless, every effort should be made towards optimization of the dynamic CTP component which is the main contributor to patient radiation burden.

[Possibilities for exposure reduction in computed tomography examination of acute chest pain]

CLINICAL/METHODICAL ISSUE

Electrocardiogram-gated (ECG) computed tomography (CT) investigations can be accompanied by high amounts of radiation exposure. This is particularly true for the investigation of patients with unclear and acute chest pain.

STANDARD RADIOLOGICAL METHODS

The common approach in patients with acute chest pain is standard spiral CT of the chest.

METHODICAL INNOVATIONS

The chest pain or triple-rule-out CT protocol is a relatively new ECG-gated protocol of the entire chest. This article reviews and discusses different techniques for the CT investigation of patients with acute chest pain.

PERFORMANCE

By applying the appropriate scan technique, the radiation exposure for an ECG-gated protocol must not necessarily be higher than a standard chest CT scan

ACHIEVEMENTS

Aortic pathologies are far better depicted by ECG-gated scan protocols and depending on the heart rate coronary artery disease can also be detected at the same time.

PRACTICAL RECOMMENDATIONS

The use of ECG-triggered scans will not support the diagnostics of the pulmonary arteries. However, in unspecific chest pain an ECG-triggered scan protocol can provide information on the differential diagnosis.

Comparison of radiation dose and image quality of triple-rule-out computed tomography angiography between conventional helical scanning and a strategy incorporating sequential scanning

Triple-rule-out computed tomographic angiography (TRO CTA), performed to evaluate the coronary arteries, pulmonary arteries, and thoracic aorta, has been associated with high radiation exposure. The use of sequential scanning for coronary computed tomographic angiography reduces the radiation dose. The application of sequential scanning to TRO CTA is much less well defined. We analyzed the radiation dose and image quality from TRO CTA performed at a single outpatient center, comparing the scans from a period during which helical scanning with electrocardiographically controlled tube current modulation was used for all patients (n = 35) and after adoption of a strategy incorporating sequential scanning whenever appropriate (n = 35). Sequential scanning was able to be used for 86% of the cases. The sequential-if-appropriate strategy, compared to the helical-only strategy, was associated with a 61.6% dose decrease (mean dose-length product of 439 mGy × cm vs 1,144 mGy × cm and mean effective dose of 7.5 mSv vs 19.4 mSv, respectively, p <0.0001). Similarly, a 71.5% dose reduction occurred among the 30 patients scanned with the sequential protocol compared to the 40 patients scanned with the helical protocol using either strategy (326 mGy × cm vs 1,141 mGy × cm and 5.5 mSv vs 19.4 mSv, respectively, p <0.0001). Although the image quality did not differ between the strategies, a nonstatistically significant trend was seen toward better quality in the sequential protocol than in the helical protocol. In conclusion, approaching TRO CTA with a diagnostic strategy of sequential scanning, as appropriate, can offer a marked reduction in the radiation dose while maintaining the image quality.