The thoracic aorta studied by MR imaging

Vessel wall imaging for intracranial vascular disease evaluation

Accurate and timely diagnosis of intracranial vasculopathies is important owing to the significant risk of morbidity with delayed and/or incorrect diagnosis both from the disease process and inappropriate therapies. Conventional luminal imaging techniques for analysis of intracranial vasculopathies are limited to evaluation of changes in the vessel lumen. Vessel wall MRI techniques can allow direct characterization of pathologic changes of the vessel wall. These techniques may improve diagnostic accuracy and improve patient outcomes. Extracranial carotid vessel wall imaging has been extensively investigated in patients with atherosclerotic disease and has been shown to accurately assess plaque composition and identify vulnerable plaque characteristics that may predict stroke risk beyond luminal stenosis alone. This review provides a brief history of vessel wall MRI, an overview of the intracranial vessel wall MRI techniques, its applications, and imaging findings of various intracranial vasculopathies pertinent to the neurointerventionalist, neurologist, and neuroradiologist. We searched MEDLINE, PubMed, and Google for English publications containing any of the following terms: 'intracranial vessel wall imaging', 'intracranial vessel wall', and 'intracranial vessel wall MRI'.

Assessment of pulmonary hypertension what CT and MRI can provide

RATIONALES AND OBJECTIVES

Pulmonary hypertension (PH) is a life-threatening condition, characterized by elevated pulmonary arterial pressure, which is confirmed based on invasive right heart catheterization (RHC). Noninvasive examinations may support diagnosis of PH before proceeding to RHC and play an important role in management and treatment of the disease. Although echocardiography is considered a standard tool in diagnosis, recent advances have made computed tomography (CT) and magnetic resonance (MR) imaging promising tools, which may provide morphologic and functional information. In this article, we review image-based assessment of PH with a focus on CT and MR imaging.

CONCLUSIONS

CT may provide useful morphologic information for depicting PH and seeking for underlying diseases. With the accumulated technological advancement, CT and MRI may provide practical tools for not only morphologic but also functional assessment of patients with PH.

Marfan's syndrome: an overview

Marfan's syndrome is an autosomal dominant condition with an estimated prevalence of one in 10,000 to 20,000 individuals. This rare hereditary connective tissue disorder affects many parts of the body. The diagnosis of Marfan's syndrome is established in accordance with a review of the diagnostic criteria, known as the Ghent nosology, through a comprehensive assessment largely based on a combination of major and minor clinical manifestations in various organ systems and the family history. Aortic root dilation and mitral valve prolapse are the main presentations among the cardiovascular malformations of Marfan's syndrome. The pathogenesis of Marfan's syndrome has not been fully elucidated. However, fibrillin-1 gene mutations are believed to exert a dominant negative effect. Therefore, Marfan's syndrome is termed a fibrillinopathy, along with other connective tissue disorders with subtle differences in clinical manifestations. The treatment may include prophylactic β-blockers and angiotensin II-receptor blockers in order to slow down the dilation of the ascending aorta, and prophylactic aortic surgery. Importantly, β-blocker therapy may reduce TGF-β activation, which has been recognized as a contributory factor in Marfan's syndrome. The present article aims to provide an overview of this rare hereditary disorder.

MR Imaging of the Aorta

Recent advances in noninvasive imaging methods, such as CT and MR imaging, have replaced most of invasive angiographic procedures in the diagnosis of acquired aortic disease, decreasing the cost and morbidity of diagnosis. This article reviews and illustrates present MR imaging methods for evaluation of the aorta. Common diseases of the aorta also are discussed with a focus on their unique morphologic and functional features and characteristic MR imaging findings. Knowledge of pathologic conditions of common aortic diseases and proper MR imaging techniques enables accurate and time-efficient aortic evaluation.

Apport de l’IRM dans l’exploration des anomalies cardiaques congénitales et des gros vaisseaux

Management of congenital heart diseases (CHD) frequently is a diagnostic challenge. MRI, as a complement to echocardiography, plays an important role in the non-invasive evaluation of these anomalies. MRI allows high resolution anatomical evaluation of these structures in multiple planes as well as functional evaluation. These features are helpful to further characterize extra-cardiac anomalies that may be difficult to assess at US and even angiography. MRI is thus a valuable imaging tool in the evaluation of CHD.

MRA of the thoracic vessels

Magnetic resonance imaging (MRI) is well suited for the noninvasive evaluation of the thoracic vasculature, and with improvements in scanner technology, the ability of MR to illustrate the thoracic vessels has significantly improved. Dedicated vascular software and pulse sequences have become commercially available, and fast imaging, in particular, has facilitated the time-efficient and comprehensive MR evaluation of most thoracic vascular lesions. Over the years, a host of black and bright blood MRI methods have evolved into practical tools for illustration of the thoracic vessels. As with other MR applications, successful vascular depiction relies significantly on the proper selection and prescription of imaging pulse sequences. In this article, these methods with their specific technical and practical pitfalls for thoracic magnetic resonance angiography (MRA) will be discussed. Current clinical indications for thoracic MRA will also be illustrated.

Magnetic resonance imaging features of aortic diseases

The usefulness of magnetic resonance imaging (MRI) for aortic diseases is discussed, with special attention given to the MRI features of aortic dissection and Takayasu arteritis. Computed tomography (CT) and MRI provide excellent visualization of vessels and their relationship to surrounding structures; however, CT depicts the vessel lumen optimally only when contrast enhancement is used. MRI, with its inherent multiplanar imaging capability, is well suited for evaluation of the thoracic and abdominal aorta and can be used with or without contrast enhancement. Basic technical considerations in cardiac imaging, which include conventional spin-echo, fast spin-echo, cine gradient, and echo-planar imaging, with time-of-flight and phase-contrast methods, are discussed and applied to aortic aneurysm, aortic dissection, and Takayasu arteritis. The diagnostic capacity of spin-echo MRI in patients with suspected aortic dissection is enhanced when it is combined with cine MRI. Despite the ability of CT and MRI to demonstrate luminal and mural changes of aortic abnormalities, conventional angiography still may be necessary at first admission for selected patients in the late occlusive phase to provide additional information on the degree and extent of the arteritis. CT angiography and MR angiography are promising imaging techniques that will overcome difficulties in visualizing distal branch vessel lesions and obviate the need for conventional angiography in the near future.

Phase-contrast cine MR angiography detection of thoracic aortic dissection

PURPOSE

To assess prospectively the accuracy of phase-contrast cine MR angiography in the detection of thoracic aortic dissection with operative correlation.

MATERIALS AND METHODS

One hundred and ninety-seven symptomatic patients suspected of having thoracic aortic dissection or aneurysm as well as 13 patients suspected of having thoracic aortic coarctation and 20 asymptomatic normals (as controls) were examined prospectively with phase-contrast cine MR angiography on a 1.5-T MR imager. Seventy-eight of these patients had operative correlation, and only these 78 patients were included in the statistical analysis.

RESULTS

There were 51 true positive and 27 true negative findings of thoracic aortic dissection in this study for an accuracy of 100%.

CONCLUSION

Phase-contrast cine MR angiography is an accurate non-invasive imaging technique for evaluating patients suspected of having thoracic aortic dissection.

MR imaging of coarctation of the aorta and its postoperative complications in adults: assessment with spin-echo and cine-MR imaging

To evaluate the ability of ECG-gated spin-echo (SE)-MR imaging vs. cine-MR imaging to assess coarctation of the aorta, 11 patients aged 15-45 years, with known or suspected coarctation of the aorta, and five patients suspected of re-stenosis or postoperative false-aneurysms after coarctation repair were examined by multisection SE-MR imaging and single-section multiphase cine-MR imaging on a 1.0 Tesla device. Aortography was performed in 15, and surgery in 14 of these 16 patients. Qualitatively, the location, severity, and length of the coarctation were shown in all cases with MR imaging, as well as the relationship with the arteries arising from the aortic arch. The respective sensitivities and specificities in the assessment of severity of stenoses were 86% and 100% for SE MR images, and 100% and 100% for cine-MR images. Cine-MR imaging was superior to SE imaging in stenosis diameter assessment with contrast angiography as reference, as well as to identify the site of leakage in cases of postoperative pseudoaneurysm. Pre-stenotic dilation or post-stenotic aneurysm, collateral channels, and associated malformations were better identified on SE images. Quantitatively, a better stenosis diameter correlation was found between cine-MR images and angiography than between SE-MR images and angiography (r=0.99 vs. r=0.78; p=0.001 vs. p=0.004), related to overestimation of stenoses with SE-MR imaging. The use of a combination of spin-echo and cine-MR imaging correlates well with conventional angiographic findings in this small series of patients with coarctation of aorta or postoperative pseudoaneurysmal complications. Cine-MRI can provide anatomic information that is equivalent to angiography for surgical planning.

Effects of morphologic restenosis, defined by MRI after coarctation repair, on blood pressure and arm-leg and Doppler gradients

Ten years after coarctation repair, 36 adolescents and young adults were studied in order to evaluate the relationship of anatomy at the resection site to blood pressure and arm-leg and Doppler gradients. The patients underwent magnetic resonance imaging (MRI), exercise testing, and continuous wave (CW) Doppler echocardiography. On MRI, residual narrowing at the resection site was measured as 1-(phi anastomosis/ phi descending aorta) and expressed as percent stenosis. Residual stenosis on MRI was negatively correlated with the leg pressure at rest (P = 0.0003) and during exercise (P = 0.002). Residual stenosis correlated positively with the arm-leg gradient at rest (P < 0.0001) and during exercise (P < 0.0001) and with the peak CW Doppler gradient across the anastomosis (P < 0.0001). However, residual stenosis was not related to the systolic blood pressure of the arm at rest or during exercise. The systolic arm pressures did not differ between patients with residual stenosis of less than 30% (group I), patients with residual stenosis of equal to or greater than 30% but less than 45% (group II), and patients with residual stenosis of equal to or greater than 45% (group III). In conclusion residual anatomic stenosis influences blood pressure in the legs, the arm-leg gradient, and the Doppler gradient across the anastomosis. Arm hypertension late after coarctation repair seems not to be related to residual stenosis, and the benefit of reintervention in these patients remains questionable.

Evaluation of thoracic aortic dissection using breath-holding cine MRI

OBJECTIVE

Our goal was to determine if breath-hold cine MRI in transaxial planes can be used for the evaluation of thoracic aortic dissection instead of conventional cine MRI since rapid imaging is required in this clinical setting.

MATERIALS AND METHODS

Twelve patients with thoracic aortic dissection were imaged using a 1.5 T imager. Breath-hold images were acquired with fast cine MR sequence (TR/TE = 9/2.8, 20 degrees flip angle) using segmented k-space data acquisition. Conventional non-breath-hold cine MR images (TR/TE = 22/7.5, 35 degrees flip angle, 2 averages) were taken with flow and respiratory compensation.

RESULTS

Sharpness of edges of the vessels on fast cine MR images was better than that on conventional cine MR images in 34 (57%) of 60 images. Inhomogeneous blood signal in aortic lumen due to motion artifacts was found in 2 (3%) of fast cine MR images and in 15 (25%) of conventional cine MR images. The contrast-to-noise ratios of fast cine MR images were significantly better than those of conventional cine MR images (26.4 +/- 9.1 vs. 18.5 +/- 10.1; p < 0.05) when the region of interest for noise was placed to include ghosting artifacts.

CONCLUSION

Breath-hold cine MRI is a rapid technique that gives high quality images of thoracic aortic dissection and can provide a diagnosis in < 10 min of imaging time.

Magnetic resonance imaging of the pediatric thoracic aorta

Magnetic resonance imaging (MRI) is an ideal imaging modality for investigating anomalies of the pediatric thoracic aorta. Its multiplanar capabilities allow imaging along anatomic or perpendicular planes, and clearly show the relationship between the great vessels and the airway structures. The most common pediatric aortic lesions investigated by MRI include vascular rings and coarctation of the descending aorta and its surgical complications. Other obstructive, aneurysmal, and positional anomalies of the aorta are readily demonstrated and quantified. However, precise image prescription is necessary to obtain optimal information. This review discusses and illustrates the common pediatric anomalies and current appropriate choices of imaging techniques.

Magnetic resonance imaging of peripheral vascular disease. The state of the artery

Peripheral vascular disease is a term often used to describe the manifestation of atherosclerosis below the bifurcation of the abdominal aorta. Peripheral atherosclerosis is a major cause of morbidity in the developed countries and 2% of adults in late middle age have intermittent claudication, which is severe enough in some patients to warrant hospital admission. The disease produces problems either by reducing blood flow or by the release of emboli from ulcerated plaques. The morphology and composition of arterial segments containing atheroma is of considerable importance. Plaques of different morphology have different effects on the arterial wall, such as the potential for thrombosis and the effect of arterial spasm. The lipid content may also affect the propensity for fissuring, ulceration, and thrombosis. In addition to discrete atherotic lesions, a localized and generalized sclerosis occurs. Sclerosis, or stiffness, can be demonstrated in experimental disease in animals and in man, and regression leads to reduced stiffness. Magnetic resonance imaging promises a comprehensive assessment of peripheral atherosclerosis noninvasively and without the use of ionizing radiation. Atheroma can be imaged directly, its size can be measured, its shape can be described, its lipid content can be assessed, and its effects upon vascular hemodynamics can be studied. In addition, arterial compliance, pulse wave velocity, and the pattern of flow within the vessel can be studied. It is thus a potential tool not only for the detection of disease but also for studying its natural history, risk factors, and the effects of pharmacological or surgical interventions.

Magnetic resonance imaging detection of aortic and pulmonary artery wall thickening in the acute stage of takayasu arteritis. Improvement of clinical and radiologic findings after steroid therapy

OBJECTIVE

Early diagnosis of Takayasu arteritis in the acute stage (prepulseless stage) is extremely difficult. Identification of a useful approach to detecting the initial changes of arteritis is therefore desirable.

METHODS

Careful clinical examination of a young woman with persistent fever and dry cough revealed faintly audible bruits at the cervical, supraclavicular, and abdominal regions. Aortographic features suggested thickening of the wall of the descending thoracic aorta. Magnetic resonance imaging (MRI) of this area was diagnostic.

RESULTS

MRI demonstrated involvement of the ascending aorta and right main pulmonary artery. Steroid therapy (prednisolone 60 mg/day) induced dramatic clinical and radiologic improvement in 2 months.

CONCLUSION

This is the first report of MRI-documented reduction in the thickness of the walls of both the aorta and the pulmonary artery following steroid therapy.

Magnetic resonance morphological, chemical shift and flow imaging in peripheral vascular disease

We have used magnetic resonance imaging to study the aorto-iliac region in 13 patients with peripheral disease. Five healthy volunteers were studied for comparison. Magnetic resonance spin-echo imaging, chemical shift imaging to determine lipid content of atheroma, phase-shift velocity mapping and quantitative flow studies were obtained and the findings compared with radiological angiograms. The velocity profiles study showed an increased velocity at the site of a stenosis in eight patients who had iliac artery disease. Quantitative flow measurements made in both iliac arteries and the aorta in five patients and five volunteers showed a flow ratio in both iliac arteries less than 0.85 in patients with a stenosis of one iliac artery and a ratio greater than 0.85 in the volunteers. In one patient studied before and after angioplasty, flow improved post-angioplasty. The flow curve showed a characteristic distortion in diseased vessels compared with healthy vessels. In the chemical shift images of aortic atheroma five were classified as fibrous and three were lipid rich. This preliminary study showed the potential of magnetic resonance to assess non-invasively the morphology, composition and the haemodynamic significance of atheroma. This could be important in the study of the progression of peripheral vascular disease and its response to pharmacological and surgical intervention and in the planning treatment of lesions.

Noninvasive assessment of coarctation of the aorta: comparative measurements by two-dimensional echocardiography, magnetic resonance, and angiography

Fifteen patients, aged between 9 and 21 years (mean, 15.1), with native coarctation of the aorta (CoA) or suspected recoarctation after surgical repair, underwent three different diagnostic procedures. Two-dimensional echocardiography (2D echo) and magnetic resonance imaging (MRI) of the thoracic aorta were performed in all patients; 14 patients underwent aortography, and digital subtraction angiography of the aorta was performed in one (after injection via a central venous catheter). Conventional electrocardiographic (ECG) gated MRI was performed, using the sagittal plane, a 256 x 256 acquisition matrix, multi-slice technique and a slice thickness of 10 mm. Diameters at the coarctation site were determined by all methods. Additional diameters of the descending aorta and the aortic arch were measured by MRI and echocardiography, respectively. All noninvasively obtained diameters were compared with angiographic data. Ultrasound imaging of the aortic isthmus was achieved in seven of 15 patients and of the aortic arch in nine of 15. The mean difference compared with angiographically determined diameters was 1.7 (0-7) mm, being greater for the coarctation site [mean, 2.2 (0-4)]. MRI images of the aortic isthmus were obtained in all patients, but the difference to angiographically determined diameters was slightly higher [mean, 3.2 mm (0-8)] than the ultrasound results. This deviation was presumably due to technical conditions, such as slice thickness and orthogonal imaging planes. Including all diameters, the correlation to invasive measurements was r = 0.82 (SEM = 3.1) for MRI and r = 0.89 (SEM = 2.3) for echo recordings.(ABSTRACT TRUNCATED AT 250 WORDS)

Postoperative evaluation of ascending aortic prosthetic conduits by magnetic resonance imaging

Operative repair of ascending thoracic aortic dissection and aneurysm often involves the placement of prosthetic aortic conduits and stents with wrapping of the native aorta around the prosthetic device. Postoperative assessment has been clinical because of the absence of an adequate noninvasive imaging modality and a reluctance to perform invasive contrast aortography. Magnetic resonance imaging was performed on ten patients after operative placement of a prosthetic ascending aortic graft. The MR images were reviewed and a grading system was devised based on appearance of the operative site. An increase in MR signal was noted in some patients between the graft and wrapped native vessel. In 20 percent of patients vascular lumen compromise was noted. Magnetic resonance imaging offers a noninvasive technique to assess postoperative complications and offers a viable alternative to invasive contrast aortography.

Magnetic resonance imaging of the heart: current status

The favorable technical capabilities of magnetic resonance imaging (MRI) make it well suited for delineating the heart and great vessels. The clinical applications of cardiac MRI have gradually expanded in the past several years. Currently, the most important applications use the modality to provide detailed morphologic information, especially about surgical lesions of the heart. Particularly noteworthy have been applications of MRI in preoperative assessment of patients with certain types of congenital heart disease, cardiac masses, and lesions of the great vessels. Other roles for the modality such as in functional cardiac imaging and nuclear magnetic resonance spectroscopy remain attractive, but these have not yet entered the domain of routine clinical practice.

Magnetic resonance imaging of isolated abdominal aortic dissection

In the absence of trauma or descending thoracic aortic dissection, abdominal aortic dissection is rare. This report presents a case of "isolated" abdominal aortic dissection. Magnetic resonance imaging may reliably diagnose and characterize these dissections without the use of contrast material.

Magnetic resonance imaging of aneurysms and chronic dissections of the thoracic aorta

Magnetic resonance imaging (MRI) was performed in 30 patients having an aneurysm or chronic dissection of the thoracic aorta. Using a magnetic field of 0.5 Tesla, multislice image acquisition was obtained by the ECG gated spin-echo imaging technique with dual-echoes. These results were retrospectively compared with those obtained in the same patients by angiography and computerized tomography (CT). In 10 cases of aneurysm, MRI measured their diameters and residual lumina and assessed the extension of the aneurysm with the same precision as CT scan and angiography. In 17 other cases, the diagnosis of chronic dissection was made by documenting an intimal flap and double channel filling of the aorta, and MRI compared favorably with CT scan. In three dissections in which the false lumen was thrombosed, MRI was unable to distinguish between dissection and partially thrombosed aneurysm. We believe MRI constitutes a useful noninvasive method for the study of aneurysms and chronic dissections of the thoracic aorta.

Preoperative evaluation of the thoracic aorta using MRI and angiography

The ability of ECG-gated magnetic resonance imaging (MRI) to evaluate disease of the thoracic aorta compared with angiography was prospectively assessed in 28 patients. MRI identified abnormalities in all patients, with confirmation at operation in 22 (79%) and by angiography alone in all 28. In 20 of the patients, MRI correctly diagnosed 20 of 21 aneurysms of the thoracic aorta (6 dissecting, 4 saccular, 10 fusiform), but 1 surgically proven fusiform aneurysm was categorized as an enlarged aortic dissection based on both MRI and angiographic findings. One dissection and 1 fusiform aneurysm were shown by MRI only. Coarctation of the aorta was identified in 4 patients. Ascending aortic enlargement and left ventricular hypertrophy were identified by MRI in 4 patients with aortic stenosis. In 7 patients (25%), MRI provided additional important information not shown by angiography and in 1 patient, the MRI findings resulted in a change in the surgical approach. In 14 of 28 patients (50%), angiography was necessary for definitive preoperative evaluation of the aortic valve, the coronary arteries, or the brachiocephalic vessels. MRI was a useful noninvasive supplement to angiography for the preoperative assessment of thoracic aortic disease.

Evaluation of balloon angioplasty of coarctation restenosis by magnetic resonance imaging

Eight patients treated by balloon angioplasty for coarctation restenosis have been followed for 4 to 54 months (mean 40) by physical examination using Doppler pressures and by magnetic resonance imaging in a superconducting magnet operating at 0.6 tesla. Image analysis was performed by inspection and by measurement of the aorta, with particular attention to the angioplasty site and its relation to the ascending aorta at the same axial level. Similar measurements were made from immediate postangioplasty angiograms. Residual pressure gradients were 0 to 12 mm (mean 2), reflecting persistent absence of a gradient in 1 patient and further gradient reduction in 7. Images showed no aneurysm formation, mild residual or recurrent stenosis in 4 patients, minimal focal periaortic soft tissue thickening in 1 patient and an interval increase in the ratio of ballooned segment diameter to ascending aortic diameter in the 7 patients in whom it could be measured. Thus, intermediate-term results of balloon dilatation of coarctation restenosis are excellent and magnetic resonance imaging is well suited to the serial studies required in these patients.

Magnetic resonance imaging of the thoracic aorta

Forty-one patients with a variety of suspected aortic lesions underwent magnetic resonance imaging (MRI) of the thoracic aorta. Patients were separated into 2 groups: Group A included 19 patients who underwent MRI after arteriography for comparison purposes and were evaluated retrospectively. Surgical confirmation was obtained in 9 of these patients. Group B included 22 patients who were studied prospectively because of abnormal chest x-ray, ultrasound or computerized tomographic findings and did not undergo arteriography before MRI. Two patients from this group had surgery. In group A, MRI correlated with the surgical or angiographic findings in 18 of 19 patients (95%). In group B, MRI was considered of diagnostic quality in all patients and no other invasive or noninvasive imaging modalities were needed for diagnosis and treatment. Thus, MRI will replace arteriography in a large proportion of patients with suspected thoracic aortic lesions.

Evaluation of an aortic annular pseudoaneurysm by MRI: comparison with echocardiography, angiography and surgery

Nuclear magnetic resonance imaging (MRI) was clinically useful in a case of aortic annular pseudoaneurysm complicating bacterial endocarditis. The MRI findings were proven by angiography and surgery. Although surgical correction was attempted, the aneurysm recurred and has been followed by MRI and two-dimensional echocardiography. In addition to two-dimensional echocardiography, MRI represents a useful noninvasive imaging method for diagnosis and follow up of aortic annular pseudoaneurysm.

Segmental absence of the aortic wall: magnetic resonance imaging sign of aneurysm

A thin-walled, posttraumatic false aneurysm of the descending aorta in a 32-year-old man was obvious on chest radiography, computed tomography, and aortography. The wall of the aneurysm was not visualized on a magnetic resonance imaging study. However, a segmental absence of the lateral wall of the descending aorta indicated the level of the abnormality. This finding was not observed on 100 consecutive normal aortas studied with gated magnetic resonance imaging. It was observed in 2 of 50 normal aortas on nongated thoracic magnetic resonance imaging.