Magnetic Resonance Imaging of Pulmonary Embolism: Diagnostic Accuracy of Unenhanced MR and Influence in Mortality Rates

Comparison of the diagnostic performance of non-contrast MR angiography and planar V/Q scintigraphy for pulmonary embolism: a systematic review and meta-analysis

OBJECTIVES

To conduct a meta-analysis of the diagnostic performance of non-contrast magnetic resonance pulmonary angiography (NC-MRPA) and ventilation-perfusion (V/Q) scintigraphy for the detection of acute pulmonary embolism (PE).

MATERIALS AND METHODS

Systematic searches of electronic databases were conducted from 2000 to 2024. Primary outcomes were per-patient sensitivity and specificity of NC-MRPA and V/Q scintigraphy. The pooled sensitivities, specificities, and 95% confidence intervals (95% CI) were calculated using a random-effect analysis. Summary receiver-operating characteristic (SROC) curves and the area under the curve (AUC) were obtained.

RESULTS

A total of 3709 studies (1941 NC-MRPA studies) were identified through systematic searches, with eight published MRI and nine published V/Q investigations meeting inclusion criteria. The results showed that NC-MRPA had a pooled sensitivity of 0.88 (95% CI: 0.83-0.91) and specificity of 0.97 (95% CI: 0.93-0.98), yielding an AUC of 0.92 (95% CI: 0.85-0.96). V/Q scanning had a pooled sensitivity of 0.81 (95% CI: 0.76-0.85) and specificity of 0.84 (95% CI: 0.74-0.91), yielding an AUC of 0.87 (95% CI: 0.75-0.91). The pooled proportion of non-diagnostic tests for V/Q scans (34.7%, 95% CI: 30.8-38.7) was greater than that of NC-MRPA studies (3.31%, 95% CI: 1.65-4.97).

CONCLUSION

This meta-analysis suggests that NC-MRPA is more specific than V/Q scintigraphy for the detection of PE, with comparable accuracy and sensitivity. NC-MRPA yielded fewer non-diagnostic scans than V/Q scintigraphy and is a feasible alternative imaging modality for diagnosing PE in patients for whom intravenous contrast administration poses a substantive risk.

KEY POINTS

Question V/Q lung scintigraphy has been used as a reserve, alternative modality for patients who cannot undergo CT pulmonary angiography. Findings Non-contrast MR angiography (MRA) is a feasible alternative for diagnosing PE in patients for whom intravenous iodinated contrast administration poses a substantial risk. Clinical relevance Non-contrast MRA provides similar sensitivity and superior specificity to V/Q scintigraphy for diagnosing PE, without ionizing radiation exposure.

Diagnostic test accuracy of imaging modalities for adults with acute pulmonary embolism: A systematic review and meta-analysis

OBJECTIVES

This systematic review and meta-analysis aimed to evaluate the current literature on diagnostic test accuracy (DTA) of imaging modalities for adults with acute pulmonary embolism (APE).

BACKGROUND

Medical imaging plays an integral role in evaluating and managing those with APE. Guidance for imaging modality use for APE diagnosis varies due to a lack of clinical standardisation. Despite this, CTPA remains the first-line imaging modality used by clinicians.

METHODS

A literature search of PubMed, EMBASE, Trove and Mednar databases (2012-2020; English language) was performed. Studies assessing the DTA of imaging modalities for APE diagnosis were included. DTA studies methodological quality was assessed using the Quality Assessment of Diagnostic Accuracy Studies 2 (QUADAS-2 tool). Results of eligible studies were pooled using random or fixed effects modelling the calculate the pooled DTA of explored imaging modalities for APE. The Higgins I² test were performed to assess between study heterogeneity.

RESULTS

10 Studies, involving 998 participants, were enrolled and pooled using the random effects model. Of the explored modalities, magnetic resonance imaging (MRI), specifically pulmonary MRI and magnetic resonance pulmonary angiography (MRPA) exhibited the highest pooled DTA. Sensitivity, specificity, negative likelihood ratio, positive likelihood ratio and diagnostic odds ratio for MRPA were 0.952 (95% CI, 0.881 to 0.987), 0.857 (95% CI, 0.637 to 0.97), 5.631 (95% CI, 2.163 to 14.659), 0.06 (95% CI, 0.007 to 0.537) and 80.310 (95% CI, 15.607 to 413.25) respectively. Based on the QUADAS-2 criteria, most studies presented low to moderate risk of bias and concern regarding applicability.

CONCLUSION

The explored ultrasound and MRI protocols which exhibit a lower radiation burden when compared to the current gold standard computed tomography pulmonary angiography (CTPA), have acceptable diagnostic accuracy for APE and can be useful in certain situations.

ACR Appropriateness Criteria® Suspected Pulmonary Embolism: 2022 Update

Pulmonary embolism (PE) remains a common and important clinical condition that cannot be accurately diagnosed on the basis of signs, symptoms, and history alone. The diagnosis of PE has been facilitated by technical advancements and multidetector CT pulmonary angiography, which is the major diagnostic modality currently used. Ventilation and perfusion scans remain largely accurate and useful in certain settings. MR angiography can be useful in some clinical scenarios and lower-extremity ultrasound can substitute by demonstrating deep vein thrombosis; however, if negative, further studies to exclude PE are indicated. In all cases, correlation with the clinical status, particularly with risk factors, improves not only the accuracy of diagnostic imaging but also overall utilization. Other diagnostic tests have limited roles. The ACR Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision process support the systematic analysis of the medical literature from peer-reviewed journals. Established methodology principles such as Grading of Recommendations Assessment, Development, and Evaluation or GRADE are adapted to evaluate the evidence. The RAND/UCLA Appropriateness Method User Manual provides the methodology to determine the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances in which peer-reviewed literature is lacking or equivocal, experts may be the primary evidentiary source available to formulate a recommendation.

Diagnostic accuracy of true fast imaging with steady-state precession, MR pulmonary angiography and volume-interpolated body examination for pulmonary embolism compared with CT pulmonary angiography

The diagnostic performance of magnetic resonance (MR) sequences for displaying different levels of pulmonary artery involvement in pulmonary embolism (PE) has rarely been reported but is essential for critically ill and emergency patients. The aim of the present study was to analyze the diagnostic accuracy of true fast imaging with steady-state precession (true FISP), MR pulmonary angiography (MRPA) and volume-interpolated body examination (VIBE) for PE detection in comparison to CT pulmonary angiography (CTPA), which is the reference standard. A total of 21 patients with confirmed deep venous thrombosis suspected of having PE were enrolled. Emboli were evaluated on per-patient and per-vessel bases. The evidence of PE on a per-vessel basis was classified into central, lobar and segmental levels, and 27 vessel segments per patient were analyzed for a total of 567 vessel segments in all patients. The sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) were calculated. Receiver operating characteristic curves were drawn to compare differences in sequences. A total of 158 pulmonary vessels were involved with emboli on CTPA, 58 of which were identified by true FISP, 63 by MRPA and 94 by VIBE. On per-patient and per-vessel bases, the sensitivity was 81.3 and 36.7%, respectively, for true FISP, 82.4 and 56.3%, respectively, for MRPA, and 94.4 and 68.1%, respectively, for VIBE; the specificity was 80.0 and 99.8%, respectively, for true FISP, 100 and 99.2%, respectively, for MRPA, and 100 and 99.2%, respectively, for VIBE. The respective PPV was 92.9 and 98.3% for true FISP, 100 and 95.5% for MRPA, 100 and 96.9% for VIBE. The NPV was 57.1 and 80.3%, respectively, for true FISP, 50.0 and 88.2%, respectively, for MRPA, and 75.0 and 89.8%, respectively, for VIBE. In conclusion, enhanced VIBE surpassed the other two sequences in revealing PE, particularly in segmental analysis, which is essential for emergency patients who have contraindications for receiving iodinated contrast and those who have concerns about the ionizing radiation.

Clinical Value of Noncontrast-Enhanced Radial Quiescent-Interval Slice-Selective (QISS) Magnetic Resonance Angiography for the Diagnosis of Acute Pulmonary Embolism Compared to Contrast-Enhanced Computed Tomography and Cartesian Balanced Steady-State Free Precession

BACKGROUND

Free-breathing noncontrast-enhanced (non-CE) magnetic resonance angiography (MRA) techniques are of considerable interest for the diagnosis of acute pulmonary embolism (APE), due to the possibility for repeated examinations, avoidance of side effects from iodine-based contrast agents, and the absence of ionizing radiation exposure as compared to CE-computed tomographic angiography (CTA).

PURPOSE

To analyze the clinical performance of free-breathing and electrocardiogram (ECG)-gated radial quiescent-interval slice-selective (QISS)-MRA compared to CE-CTA and to Cartesian balanced steady-state free precession (bSSFP)-MRA.

STUDY TYPE

Prospective.

SUBJECTS

Thirty patients with confirmed APE and 30 healthy volunteers (HVs).

FIELD STRENGTH/SEQUENCE

Radial QISS- and bSSFP-MRA at 1.5T.

ASSESSMENT

Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were computed to compare the pulmonary imaging quality between MRA methods. The pulmonary arterial tree was divided into 25 branches and an ordinal scoring system was used to assess the image quality of each pulmonary branch. The clinical performance of the two MRA techniques in accurately assessing APE was evaluated with respect to CE-CTA as the clinical reference standard.

STATISTICAL TESTS

Wilcoxon signed-rank and Spearman's correlation tests were performed. Sensitivity and specificity of the MRA techniques were determined using CE-CTA as the clinical reference standard.

RESULTS

Thrombus-mimicking artifacts appeared more frequently in lobar and peripheral arteries of patients with Cartesian bSSFP than with radial QISS-MRA (pulmonary trunk: 12.2% vs. 14.0%, P = 0.64; lobar arteries: 35.6% vs. 22.0%, P = 0.005, peripheral arteries: 74.4% vs. 49.0%, P < 0.001). The relative increases in SNR and of CNR provided by radial QISS-MRA with respect to Cartesian bSSFP-MRA were 30-35% (P-values of SNR/CNR, HVs: 0.09/0.09, patients: 0.03/0.02). The image quality of pulmonary arterial branches was considered good to excellent in 77.2% of patients with radial QISS-MRA and in 43.2% with Cartesian bSSFP-MRA (P < 0.0001). The clinical performance of radial QISS-MRA was higher than Cartesian bSSFP-MRA for grading embolism, with a total sensitivity of 86.0% vs. 80.6% and a specificity of 93.3% vs. 84.0%, respectively.

DATA CONCLUSION

Radial QISS-MRA is a reliable and safe non-CE angiographic technique with promising clinical potential compared to Cartesian bSSFP-MRA and as an alternative technique to CE-CTA for the diagnosis of APE.

LEVEL OF EVIDENCE

1 TECHNICAL EFFICACY STAGE: 3.

Multimodal indirect imaging signs of pulmonary embolism

The clinical diagnosis of pulmonary embolism is often difficult, as symptoms range from syncope and chest pain to shock and sudden death. Adding complexity to this picture, some patients with non-diagnosed pulmonary embolism may undergo unenhanced imaging examinations for a number of reasons, including the prevention of contrast medium-related nephrotoxicity, anaphylactic/anaphylactoid reactions and nephrogenic systemic fibrosis, as well as due to patients' refusal or lack of venous access. In this context, radiologists' awareness and recognition of indirect signs are cornerstones in the diagnosis of pulmonary embolism. This article describes the indirect signs of pulmonary embolism on chest X-ray, unenhanced CT, and MRI.

Comparison of acquisition protocols for ventilation/perfusion SPECT-a Monte Carlo study

One of the most commonly used imaging techniques for diagnosing pulmonary embolism (PE) is ventilation/perfusion (V/P) scintigraphy. The aim of this study was to evaluate the performance of the currently used imaging protocols for V/P single photon emission computed tomography (V/P SPECT) at two nuclear medicine department sites and to investigate the effect of altering important protocol parameters. The Monte Carlo technique was used to simulate 4D digital phantoms with perfusion defects. Six imaging protocols were included in the study and a total of 72 digital patients were simulated. Six dually trained radiologists/nuclear medicine physicians reviewed the images and reported all perfusion mismatch findings. The radiologists also visually graded the image quality. No statistically significant differences in diagnostic performance were found between the studied protocols, but visual grading analysis pointed out one protocol as significantly superior to four of the other protocols. Considering the study results, we have decided to harmonize our clinical protocols for imaging patients with suspected PE. The administered Technegas and macro aggregated albumin activities have been altered, a low energy all purpose collimator is used instead of a low energy high resolution collimator and the acquisition times have been lowered.

Thoracic calcifications on magnetic resonance imaging: correlations with computed tomography

OBJECTIVE

To identify the characteristics of thoracic calcifications on magnetic resonance (MR) imaging, as well as correlations between MR imaging and CT findings.

METHODS

This was a retrospective study including data on 62 patients undergoing CT scans and MR imaging of the chest at any of seven hospitals in the Brazilian states of Rio Grande do Sul, São Paulo, and Rio de Janeiro between March of 2014 and June of 2016 and presenting with calcifications on CT scans. T1- and T2-weighted MR images (T1- and T2-WIs) were semiquantitatively analyzed, and the lesion-to-muscle signal intensity ratio (LMSIR) was estimated. Differences between neoplastic and non-neoplastic lesions were analyzed.

RESULTS

Eighty-four calcified lesions were analyzed. Mean lesion density on CT was 367 ± 435 HU. Median LMSIRs on T1- and T2-WIs were 0.4 (interquartile range [IQR], 0.1-0.7) and 0.2 (IQR, 0.0-0.7), respectively. Most of the lesions were hypointense on T1- and T2-WIs (n = 52 [61.9%] and n = 39 [46.4%], respectively). In addition, 19 (22.6%) were undetectable on T1-WIs (LMSIR = 0) and 36 (42.9%) were undetectable on T2-WIs (LMSIR = 0). Finally, 15.5% were hyperintense on T1-WIs and 9.5% were hyperintense on T2-WIs. Median LMSIR was significantly higher for neoplastic lesions than for non-neoplastic lesions. There was a very weak and statistically insignificant negative correlation between lesion density on CT and the following variables: signal intensity on T1-WIs, LMSIR on T1-WIs, and signal intensity on T2-WIs (r = -0.13, p = 0.24; r = -0.18, p = 0.10; and r = -0.16, p = 0.16, respectively). Lesion density on CT was weakly but significantly correlated with LMSIR on T2-WIs (r = -0.29, p < 0.05).

CONCLUSIONS

Thoracic calcifications have variable signal intensity on T1- and T2-weighted MR images, sometimes appearing hyperintense. Lesion density on CT appears to correlate negatively with lesion signal intensity on MR images.

Magnetic resonance imaging of interstitial lung diseases: A state-of-the-art review

Magnetic resonance imaging (MRI) has been emerging as an imaging modality to assess interstitial lung diseases (ILD). An optimal chest MRI protocol for ILDs should include non-contrast breath-holding sequences, steady-state free-precession sequences, and contrast-enhanced sequences. One of the main MRI applications in ILDs is the differentiation between areas of active inflammation (i.e. reversible stage) and fibrosis. Alveolitis presents high signal intensity on T2-weighted sequences (WS) and early-enhancement on contrast-enhanced MR sequences, while fibrotic-predominant lesions present low signal and late-enhancement in these sequences, respectively. MRI can be useful in connective tissue diseases, idiopathic pulmonary fibrosis, and sarcoidosis. The aim of this state-of-the-art review was to perform a state-of-the-art review on the use of MRI in ILDs, and propose the optimal MRI protocols for imaging ILDs.

Tales from the Night:: Emergency MR Imaging in Pediatric Patients after Hours

Overnight in-house radiology has rapidly become an important part of contemporary practice models, and is increasingly the norm in pediatric radiology. MR imaging is an indispensable first-line and problem-solving tool in the pediatric population. This has led to increasingly complex MR imaging being performed "after hours" on pediatric patients. This article reviews the factors that have led to widespread overnight subspecialty radiology and the associated challenges for overnight radiologists, and provides an overview of up-to-date imaging techniques and imaging findings of the most common indications for emergent MR imaging in the pediatric population.

"Pulmonary Vein Sign" for Pulmonary Embolism Diagnosis in Computed Tomography Angiography

PURPOSES

Considering that pulmonary arterial obstruction decreases venous flow, we hypothesized that filling defects in pulmonary veins can be identified in areas adjacent to pulmonary embolism (PE). This sign was named the "pulmonary vein sign" (PVS), and we evaluated its prevalence and performance for PE diagnosis in computed tomography pulmonary angiography (CTPA).

METHODS

This retrospective study enrolled consecutive patients with clinical suspicion of PE who underwent CTPA scan. The PVS was defined by the following criteria: (a) presence of a homogeneous filling defect of at least 2 cm in a pulmonary vein; (b) attenuation of the left atrium > 160 Hounsfield units. Using the cases that presented PE on CTPA as reference, sensitivity, specificity, and positive and negative predictive values were calculated for PVS.

RESULTS

In total, 119 patients (73 female; mean age, 62 years) were included in this study. PE was diagnosed in 44 (35.8%) patients. The PVS was present in 16 out of 44 patients with PE. Sensitivity was 36.36% (95% confidence interval (CI) 22.83-52.26%); specificity, 98.67% (95% CI 91.79-99.93%); positive predictive value, 94.12% (95% CI 69.24-99.69%); negative predictive value, 72.55% (95% CI 62.67-80.70%). The Kappa index for the PVS was good (0.801; 95% CI 0.645-0.957). PVS was correlated with lobar and segmental pulmonary embolism (p < 0.01).

CONCLUSION

Despite a low sensitivity, presence of the pulmonary vein sign was highly specific for PE, with a good agreement between readers. This sign could contribute for PE diagnosis on CTPA studies.

How to train radiology residents to diagnose pulmonary embolism using a dedicated MRI protocol

Background

In recent years, magnetic resonance imaging (MRI) has been suggested as an alternative to computed tomography angiography (CTA) to diagnose pulmonary embolism (PE). In previous studies, only senior radiologists have been evaluated as reviewers.

Purpose

To investigate if radiology residents can be trained to review MRI regarding PE and to determine the learning curve effects.

Material and Methods

Four residents independently went through a training program consisting of 70 participants that had undergone steady-state free precession MRI. The individuals were randomized into ten training sessions. For each exam, the review time and presence or absence of embolus was recorded. After completing each session, the residents received feedback on diagnostic accuracy compared to a consensus reading by two specialists. The residents were also presented with the corresponding CTA.

Results

The review time was nearly halved (P = 0.0002) during the training program. Comparing the first three sessions with the last three sessions for all residents, the review time decreased from 5:22 min to 2:51 min. The inter-reader agreement improved for all residents during the training program reaching a clinically acceptable level after seven sessions.

Conclusion

Our study suggests that radiology residents can be trained to independently review MRI investigations regarding PE within a short training program. Similar training programs could be more extensively used as effective teaching method for residents.

"Pulmonary embolism diagnostics of pregnant patients: What is the recommended clinical pathway considering the clinical value and associated radiation risks of available imaging tests?"

Pulmonary embolism (PE) during pregnancy remains the leading preventable cause of maternal morbidity and mortality in the developed countries. Diagnosis of PE in pregnant patients is a challenging clinical problem, since pregnancy-related physiologic changes can mimic signs and symptoms of PE. Patient mismanagement may result into unjustified anticoagulant treatment or unnecessary imaging tests involving contrast-related or/and radiation-related risks for both the expectant mother and embryo/fetus. On the other hand, missing or delaying diagnosis of PE could lead to life-threatening conditions for both the mother and the embryo/fetus. Thus, a timely and accurate diagnostic approach is required for the optimal management of pregnant patients with suspected PE. Aim of the current review is to discuss a pregnancy-specific clinical pathway for the early diagnosis of PE with non-ionizing radiation- and ionizing radiation-based imaging modalities taking into account previously reported data on diagnostic value of available imaging tests, and radiation related concerns.