James F. M. Meaney

DIAGNOSIS OF PULMONARY EMBOLISM WITH MAGNETIC RESONANCE ANGIOGRAPHY

BACKGROUND Diagnosing pulmonary embolism may be difficult, because there is no reliable noninvasive imaging method. We compared a new noninvasive method, gadolinium-enhanced pulmonary magnetic resonance angiography, with standard pulmonary angiography for diagnosing pulmonary embolism. METHODS A total of 30 consecutive patients with suspected pulmonary embolism underwent both standard pulmonary angiography and magnetic resonance angiography during the pulmonary arterial phase at the time of an intravenous bolus of gadolinium. All magnetic resonance images were reviewed for the presence or absence of pulmonary emboli by three independent reviewers who were unaware of the findings on standard angiograms. RESULTS Pulmonary embolism was detected by standard pulmonary angiography in 8 of the 30 patients in whom pulmonary embolism was suspected. All 5 lobar emboli and 16 of 17 segmental emboli identified on standard angiograms were also identified on magnetic resonance images. Two of the three reviewers reported one false positive magnetic resonance angiogram each. As compared with standard pulmonary angiography, the three sets of readings had sensitivities of 100, 87, and 75 percent and specificities of 95, 100, and 95 percent, respectively. The interobserver correlation was good (k=0.57 to 0.83 for all vessels, 0.49 to 1.0 for main and lobar vessels, and 0.40 to 0.81 for segmental vessels). CONCLUSIONS In this preliminary study, gadolinium-enhanced magnetic resonance angiography of the pulmonary arteries, as compared with conventional pulmonary angiography, had high sensitivity and specificity for the diagnosis of pulmonary embolism. This new technique shows promise as a noninvasive method of diagnosing pulmonary embolism without the need for ionizing radiation or iodinated contrast material.

Use of magnetic resonance angiography to select candidates with recently symptomatic carotid stenosis for surgery: systematic review

Abstract Objective: To determine if sufficient evidence exists to support the use of magnetic resonance angiography as a means of selecting patients with recently symptomatic high grade carotid stenosis for surgery. Design: Systematic review of published research on the diagnostic performance of magnetic resonance angiography, 1990-9. Main outcome measures: Performance characteristics of diagnostic test. Results: 126 potentially relevant articles were identified, but many articles failed to examine the performance of magnetic resonance angiography as a diagnostic test at the surgical decision thresholds used in major clinical trials on endarterectomy. 26 articles were included in a meta-analysis that showed a maximal joint sensitivity and specificity of 99% (95% confidence interval 98% to 100%) for identifying 70-99% stenosis and 90% (81% to 99%) for identifying 50-99% stenosis. Only four articles evaluated contrast enhanced magnetic resonance angiography. Conclusions: Magnetic resonance angiography is accurate for selecting patients for carotid endarterectomy at the surgical decision thresholds established in the major endarterectomy trials, but the evidence is not very robust because of the heterogeneity of the studies included. Research is needed to determine the diagnostic performance of the most recent developments in magnetic resonance angiography, including contrast enhanced techniques, as well as to assess the impact of magnetic resonance angiography on surgical decision making and outcomes. What is already known on this topic Carotid endarterectomy for recently symptomatic carotid stenosis is beneficial in patients with 70-99% stenosis as measured by conventional angiography It is not known whether the less invasive imaging technique of magnetic resonance angiography can accurately identify patients who will benefit from surgery What this study adds Magnetic resonance angiography is highly sensitive and specific in diagnosing 70-99% carotid stenosis However, the studies on which this conclusion is based are of low quality and high heterogeneity

Magnetic resonance angiography of the peripheral arteries: current status.

Abstract. Comprehensive imaging of the peripheral vasculature has traditionally only been possible with catheter angiography. With the introduction of time-of-flight magnetic resonance angiography (TOF MRA), non-invasive imaging of the peripheral arteries became a clinical reality; however, widespread adoption of TOF MRA did not occur due to long scan times and artefacts which precluded its use as a screening tool. Contrast-enhanced MRA, an extremely time-efficient technique with minimal associated artefacts, addresses most of the limitations of non-contrast techniques. Numerous technological advances, including bolus detection, optimized 3D volume placement, improved k-space filling mechanisms and the evolution from single-station to multi-location moving-table contrast-enhanced MRA, have facilitated the development of non-invasive evaluation of the peripheral vascular tree with contrast-enhanced techniques.

Pulmonary magnetic resonance angiography

Early attempts to image the pulmonary vasculature with spin‐echo magnetic resonance (MR) imaging were hampered by severe image degradation related to respiratory and cardiac pulsation artifact, susceptibility at interfaces between lung parenchyma and vessel wall, and poor contrast between flowing blood and intravascular filling defects of emboli. With the development of gradient‐echo MR angiographic techniques some of these limitations were overcome; however, the need for multiple breath‐holds and the frequent occurrence of flow‐related artifacts that could simulate pulmonary emboli diminished their clinical utility. With the development of contrast‐enhanced MR angiography, many of the limitations of earlier techniques were addressed. Images of both lungs with high signal‐to‐noise ratios and high contrast between flowing blood and pulmonary emboli could be acquired in a single breath‐hold, during “first‐pass” imaging with extracellular contrast agents in the coronal plane. However, subsegmental vessels could not be assessed with this approach. The technique has been refined further by imaging each lung separately in the sagittal plane; this offers higher resolution and total lung coverage and requires a shorter breath‐hold. Finally, several investigators have reported preliminary data on imaging of the pulmonary vasculature with blood pool agents, exploiting respiratory triggering or navigator echoes to eliminate the need for breath‐holding for the detection of pulmonary emboli. J. Magn. Reson. Imaging 10:326–338, 1999.

Non-invasive evaluation of the visceral arteries with magnetic resonance angiography.

Abstract. Traditionally, there have been only a few indications for imaging of the visceral arteries. With improvements in treatment of many mesenteric vascular disorders, it has become more important to establish a diagnosis early in the course of the disease. With the advent of ultrasound, computed tomography and magnetic resonance imaging non-invasive imaging of the visceral arteries became possible, although all these modalities were limited in scope for demonstration of mesenteric pathology. The advent of high-quality mesenteric MR arteriography and venography, which allows comprehensive evaluation of both visceral artery anatomy and function, has led to a huge increase in the number of studies directed at the mesenteric arteries in many departments.