Breath-hold ultrafast three-dimensional gadolinium-enhanced MR angiography of the aorta and the renal and other visceral abdominal arteries

European guidelines on chronic mesenteric ischaemia - joint United European Gastroenterology, European Association for Gastroenterology, Endoscopy and Nutrition, European Society of Gastrointestinal and Abdominal Radiology, Netherlands Association of Hepatogastroenterologists, Hellenic Society of Gastroenterology, Cardiovascular and Interventional Radiological Society of Europe, and Dutch Mesenteric Ischemia Study group clinical guidelines on the diagnosis and treatment of patients with chronic mesenteric ischaemia

Chronic mesenteric ischaemia is a severe and incapacitating disease, causing complaints of post-prandial pain, fear of eating and weight loss. Even though chronic mesenteric ischaemia may progress to acute mesenteric ischaemia, chronic mesenteric ischaemia remains an underappreciated and undertreated disease entity. Probable explanations are the lack of knowledge and awareness among physicians and the lack of a gold standard diagnostic test. The underappreciation of this disease results in diagnostic delays, underdiagnosis and undertreating of patients with chronic mesenteric ischaemia, potentially resulting in fatal acute mesenteric ischaemia. This guideline provides a comprehensive overview and repository of the current evidence and multidisciplinary expert agreement on pertinent issues regarding diagnosis and treatment, and provides guidance in the multidisciplinary field of chronic mesenteric ischaemia.

Clinical utility of optimized three-dimensional T1-, T2-, and T2*-weighted sequences in spinal magnetic resonance imaging

This article reviews the clinical utility of 3D magnetic resonance imaging (MRI) sequences optimized for the evaluation of various intraspinal lesions. First, intraspinal tumors with hypervascular components and arteriovenous malformations (AVM) are clearly shown on contrast-enhanced (CE)-3D T1-weighted gradient-echo (GE) sequences with high spatial resolution. Second, dynamic CE-3D time-resolved magnetic resonance angiography (MRA) shows delineated feeding arteries of intraspinal AVM or arteriovenous fistula (AVF), greatly aiding subsequent digital subtraction angiography (DSA). Third, 3D multiecho T2*-weighted GE sequences are used to visualize intraspinal structures and spinal cord lesions and are sensitive to the magnetic susceptibility of intraspinal hemorrhages. Three-dimensional balanced steady-state free precession (SSFP) and multishot 3D balanced non-SSFP sequences produce contiguous thin images with high signal-to-noise ratio (SNR) in short scanning times. Intraspinal cystic lesions and small nerve-root tumors in subarachnoid space can be viewed using 3D balanced SSFP. Spinal cord myelomalacia and cord compression can be evaluated on fat-suppressed multishot 3D balanced non-SSFP. Finally, a 3D T2-weighted fast spin-echo (FSE) sequence with variable flip angle (FA) refocusing pulse improves through-plane spatial resolution over conventional 2D T2-weighted FSE sequences while matching image contrast.

Vascular imaging of the mesenteric vasculature

Imaging of the mesenteric vasculature is crucial in diagnosing vascular disease of the gastro-intestinal tract such as acute or chronic mesenteric ischemia caused by arterial stenosis, embolism or thrombosis, mesenteric vein thrombosis and mesenteric aneurysm or dissection. The reference standard for imaging of the mesenteric vasculature is digital subtraction angiography. However, modalities as duplex ultrasonography, computed tomography angiography and magnetic resonance angiography are developing rapidly and may provide accurate imaging non-invasively. This review provides an up-to-date overview of the anatomic resolution, clinical application, emerging techniques and future perspectives of these four radiological modalities for imaging of the mesenteric vasculature.

Cardiovascular Imaging: The Past and the Future, Perspectives in Computed Tomography and Magnetic Resonance Imaging

Today's noninvasive imaging of the cardiovascular system has revolutionized the approach to various diseases and has substantially affected prognostic information. Cardiovascular magnetic resonance (MR) and computed tomographic (CT) imaging are at center stage of these approaches, although 5 decades ago, these technologies were unheard of. Both modalities had their inception in the 1970s with a primary focus on noncardiovascular applications. The technical development of the various decades, however, substantially pushed the envelope for cardiovascular MR and CT applications. Within the past 10-15 years, MR and CT technologies have pushed each other in cardiac applications; and without the "rival" modality, neither one would likely not have reached its potential today. This view on the history of MR and CT in the field of cardiovascular applications provides insight into the story of success of applications that once have been ideas only but are at prime time today.

Anatomic and radiologic review of chronic mesenteric ischemia and its treatment

Chronic mesenteric ischemia (CMI) is a vascular occlusive disease process that generally affects the elderly population. Clinical presentation occurs when two of the three mesenteric arteries are affected and includes non-specific abdominal pain and weight loss. The most common cause of CMI is atherosclerotic arterial occlusion. The aim of this review is to present the vascular anatomy of the mesenteric arterial circulation including the different collateral pathways. The imaging findings and the different treatment options with a brief review of the literature is presented.

[Optimal Imaging Parameters and the Advantage of Renal Artery Image Using Time-spatial Labeling Inversion Pulse at 3 Tesla Magnetic Resonance Imaging: Comparison of Image Quality for 1.5 Tesla Magnetic Resonance Imaging]

With the recent spread of three tesla (3 T) magnetic resonance imaging (MRI), time-spatial labeling inversion pulse (Time-SLIP) technique at high magnetic field can be used. The purpose of this study was to determine appropriate renal artery imaging parameters and to compare with the 1.5 T MRI image quality of a renal artery using the Time-SLIP technique. The imaging sequence was 3D true steady-state free precession (True SSFP), and using respiratory gated by the voice instructions of breath interval 2, 4, 6 seconds. We measured the fat signals when changing the values of short TI inversion recovery (STIR TI), the renal artery and renal parenchyma signals when changing the values of black blood time interval (BBTI), and contrast-to-noise ratio (CNR) between renal artery and background in 11 healthy volunteers. Visual evaluation using a 4-stage score at renal artery in clinical cases was performed. 3 T MRI is compared with a 1.5 T MRI, and the null point of STIR TI value is 60 ms extension, null point of BBTI value in the renal parenchyma was an extension of 250 ms in any of the breath interval. In flow effect, there is no difference in the 1.5 T MRI and 3 T MRI, peaked at BBTI value 1500 ms. CNR and visual evaluation were better than 3 T MRI. 3 T MRI showed a better image quality by the background signal suppression effect of the extension of the T₁ value.

Society for Vascular Surgery practice guidelines for atherosclerotic occlusive disease of the lower extremities: management of asymptomatic disease and claudication

Peripheral arterial disease (PAD) continues to grow in global prevalence and consumes an increasing amount of resources in the United States health care system. Overall rates of intervention for PAD have been rising steadily in recent years. Changing demographics, evolution of technologies, and an expanding database of outcomes studies are primary forces influencing clinical decision making in PAD. The management of PAD is multidisciplinary, involving primary care physicians and vascular specialists with varying expertise in diagnostic and treatment modalities. PAD represents a broad spectrum of disease from asymptomatic through severe limb ischemia. The Society for Vascular Surgery Lower Extremity Practice Guidelines committee reviewed the evidence supporting clinical care in the treatment of asymptomatic PAD and intermittent claudication (IC). The committee made specific practice recommendations using the GRADE (Grades of Recommendation Assessment, Development and Evaluation) system. There are limited Level I data available for many of the critical questions in the field, demonstrating the urgent need for comparative effectiveness research in PAD. Emphasis is placed on risk factor modification, medical therapies, and broader use of exercise programs to improve cardiovascular health and functional performance. Screening for PAD appears of unproven benefit at present. Revascularization for IC is an appropriate therapy for selected patients with disabling symptoms, after a careful risk-benefit analysis. Treatment should be individualized based on comorbid conditions, degree of functional impairment, and anatomic factors. Invasive treatments for IC should provide predictable functional improvements with reasonable durability. A minimum threshold of a >50% likelihood of sustained efficacy for at least 2 years is suggested as a benchmark. Anatomic patency (freedom from restenosis) is considered a prerequisite for sustained efficacy of revascularization in IC. Endovascular approaches are favored for most candidates with aortoiliac disease and for selected patients with femoropopliteal disease in whom anatomic durability is expected to meet this minimum threshold. Conversely, caution is warranted in the use of interventions for IC in anatomic settings where durability is limited (extensive calcification, small-caliber arteries, diffuse infrainguinal disease, poor runoff). Surgical bypass may be a preferred strategy in good-risk patients with these disease patterns or in those with prior endovascular failures. Common femoral artery disease should be treated surgically, and saphenous vein is the preferred conduit for infrainguinal bypass grafting. Patients who undergo invasive treatments for IC should be monitored regularly in a surveillance program to record subjective improvements, assess risk factors, optimize compliance with cardioprotective medications, and monitor hemodynamic and patency status.

Renal artery stenosis: imaging options, pitfalls, and concerns

Renal artery stenosis can be diagnosed with multiple imaging modalities, each one having different risk vs accuracy tradeoffs. Catheter angiography with pressure gradient measurements is the definitive gold standard but also the most invasive and thus reserved primarily for imaging at the time of renal revascularization. Ultrasonography is the safest and least expensive but also the least accurate and most operator-dependent. Contrast-enhanced computed tomographic angiography and magnetic resonance angiography are intermediate (between ultrasound and catheter angiography) with respect to accuracy and expense. Exciting new advances in magnetic resonance that include new contrast agents, which eliminate nephrogenic systemic fibrosis risk, and techniques to characterize the hemodynamic significance of renal artery stenoses are now becoming available. In addition, magnetic resonance angiography without any contrast has become more accurate and rivals contrast-enhanced techniques in some patients. This review explores these techniques for renal artery stenosis imaging.

Contrast-enhanced MRA of the renal and aorto-iliac-femoral arteries: comparison of gadobenate dimeglumine and gadofosveset trisodium

RATIONALE AND OBJECTIVES

Dedicated contrast agents are now available for contrast-enhanced magnetic resonance angiography (CE-MRA). This study retrospectively compares the safety and diagnostic performance data from Phase III regulatory trials performed to evaluate gadobenate dimeglumine (MultiHance(®)) and gadofosveset trisodium (Vasovist®)) for renal and peripheral CE-MRA.

MATERIALS AND METHODS

Similar examination and blinded assessment methodology was utilized in all studies to determine the safety and diagnostic performance of the agents for detection of significant (>50%) steno-occlusive disease. Digital Subtraction Angiography (DSA) was used as the standard of truth. Diagnostic performance data (sensitivity, specificity, predictive values [PVs], and likelihood ratios [LRs]) were compared (Chi-square test).

RESULTS

CE-MRA with gadobenate dimeglumine was more specific (92.4% vs. 80.5%, p < 0.0001) and accurate (83.6% vs. 77.1%, p = 0.022) than CE-MRA with gadofosveset in the detection of significant renal artery stenosis. The average sensitivity was higher for gadofosveset (74.4% vs. 67.3%, p = 0.011) in peripheral vessels although gadobenate dimeglumine was more specific (93.0% vs. 88.2%, p < 0.0001) with no difference in accuracy (86.6% vs. 86.3%, p = 0.66). PPVs were higher (p < 0.0001) for gadobenate dimeglumine in both vascular territories. Pre- to post-test shifts in the probability of detecting significant disease were greater after gadobenate dimeglumine. Adverse events in the renal and peripheral studies were reported by 9.2% and 7.7% of patients after gadobenate dimeglumine compared with 30.3% and 22.1% of patients after gadofosveset.

CONCLUSION

The diagnostic performance of CE-MRA for the detection of significant steno-occlusive disease is similar with gadofosveset and gadobenate dimeglumine although the rate of adverse events appears higher with gadofosveset.

The role of noninvasive vascular imaging in splanchnic and mesenteric pathology

Traditionally, catheter angiography (CA) has been the mainstay of diagnosis for mesenteric arterial diseases. However, CA is invasive and is associated with complications that result from the procedure itself, depending on the experience of the operators, site of vascular access, ionized radiation that could be significant when combined with interventional procedures, and administered contrast material. During the past 2 decades, technical improvements in computed tomography (CT) and magnetic resonance hardware and methods have contributed new, noninvasive tools, specifically CT angiography (CTA) and 3-dimensional gadolinium-enhanced magnetic resonance angiography (3D Gd-MRA). This article outlines the current applications, strengths, and weaknesses of CTA and 3D Gd-MRA in imaging of the mesenteric vessels.

Diagnosis and management of splanchnic ischemia

Splanchnic or gastrointestinal ischemia is rare and randomized studies are absent. This review focuses on new developments in clinical presentation, diagnostic approaches, and treatments. Splanchnic ischemia can be caused by occlusions of arteries or veins and by physiological vasoconstriction during low-flow states. The prevalence of significant splanchnic arterial stenoses is high, but it remains mostly asymptomatic due to abundant collateral circulation. This is known as chronic splanchnic disease (CSD). Chronic splanchnic syndrome (CSS) occurs when ischemic symptoms develop. Ischemic symptoms are characterized by postprandial pain, fear of eating and weight loss. CSS is diagnosed by a test for actual ischemia. Recently, gastro-intestinal tonometry has been validated as a diagnostic test to detect splanchnic ischemia and to guide treatment. In single-vessel CSD, the complication rate is very low, but some patients have ischemic complaints, and can be treated successfully. In multi-vessel stenoses, the complication rate is considerable, while most have CSS and treatment should be strongly considered. CT and MR-based angiographic reconstruction techniques have emerged as alternatives for digital subtraction angiography for imaging of splanchnic vessels. Duplex ultrasound is still the first choice for screening purposes. The strengths and weaknesses of each modality will be discussed. CSS may be treated by minimally invasive endoscopic treatment of the celiac axis compression syndrome, endovascular antegrade stenting, or laparotomy-assisted retrograde endovascular recanalization and stenting. The treatment plan is highly individualized and is mainly based on precise vessel anatomy, body weight, co-morbidity and severity of ischemia.

Bolus shaping of contrast medium to adapt k-space sampling: adjusting injection protocol of magnetic resonance angiography for optimal images in a 3-T system

PURPOSE

To explore the possibility of shaping bolus of contrast medium to adapt k-space sampling to improve image quality in a 3-T system.

MATERIALS AND METHODS

Eighty patients suspected of having renal arterial disease or atherosclerosis were divided into four groups and underwent imaging with different high-spatial-resolution three-dimensional contrast-enhanced magnetic resonance angiography (MRA) scanning and injection protocol combinations. A group of 20 patients were injected single-dose contrast medium with a centric view ordering for k-space filling. Another group of 20 patients underwent MRA with double-dose and centric-view ordering. The bolus of contrast medium was shaped by adjusting injection protocol to adapt centric and sequential view ordering of sampling k-space, respectively, for other two groups. Then, the quality of image got with different protocols combination was compared, and the dose of contrast medium used in latter two groups was compared with single- and double-dose prescription basing on body weight.

RESULT

Bolus shaped adapting to centric view ordering and sequential view ordering brings more homogeneous vessel signal. Individualized dose is lower than the double dose but higher than the single dose. Dose does not necessarily correlate with body weight.

CONCLUSION

Under certain scanning protocol, appropriate shape of contrast medium passing through target vessel leads to higher-quality image and save contrast medium.

Renal artery stenosis evaluation: diagnostic performance of gadobenate dimeglumine-enhanced MR angiography--comparison with DSA

PURPOSE

To prospectively determine diagnostic performance and safety of contrast material-enhanced (CE) magnetic resonance (MR) angiography with 0.1 mmol per kilogram of body weight gadobenate dimeglumine for depiction of significant steno-occlusive disease (> or =51% stenosis) of renal arteries, with digital subtraction angiography (DSA) as reference standard.

MATERIALS AND METHODS

This multicenter study was approved by local institutional review boards; all patients provided written informed consent. Patient enrollment and examination at centers in the United States complied with HIPAA. Two hundred ninety-three patients (154 men, 139 women; mean age, 61.0 years) with severe hypertension (82.2%), progressive renal failure (11.3%), and suspected renal artery stenosis (6.5%) underwent CE MR angiography with three-dimensional spoiled gradient-echo sequences after administration of 0.1 mmol/kg gadobenate dimeglumine at 2 mL/sec. Anteroposterior and oblique DSA was performed in 268 (91.5%) patients. Three independent blinded reviewers evaluated CE MR angiographic images. Sensitivity, specificity, and accuracy of CE MR angiography for detection of significant steno-occlusive disease (> or =51% vessel lumen narrowing) were determined at segment (main renal artery) and patient levels. Positive and negative predictive values and positive and negative likelihood ratios were determined. Interobserver agreement was analyzed with generalized kappa statistics. A safety evaluation (clinical examination, electrocardiogram, blood and urine analysis, monitoring for adverse events) was performed.

RESULTS

Of 268 patients, 178 who were evaluated with MR angiography and DSA had significant steno-occlusive disease of renal arteries at DSA. Sensitivity, specificity, and accuracy of CE MR angiography for detection of 51% or greater stenosis or occlusion were 60.1%-84.1%, 89.4%-94.7%, and 80.4%-86.9%, respectively, at segment level. Similar values were obtained for predictive values and for patient-level analyses. Few CE MR angiographic examinations (1.9%-2.8%) were technically inadequate. Interobserver agreement for detection of significant steno-occlusive disease was good (79.9% agreement; kappa = 0.69). No safety concerns were noted.

CONCLUSION

CE MR angiography performed with 0.1 mmol/kg gadobenate dimeglumine, compared with DSA, is safe and provides good sensitivity, specificity, and accuracy for detection of significant renal artery steno-occlusive disease.

Efficacy and safety of gadodiamide (Gd-DTPA-BMA) in renal 3D-magnetic resonance angiography (MRA): a phase II study

PURPOSE

To determine the most efficacious dose of gadodiamide for three-dimensional (3D) contrast-enhanced (CE) magnetic resonance angiography (MRA) of the renal arteries on a patient level based on the sensitivity in detecting the main hemodynamically relevant (> or =50% or occlusion) renal artery stenosis (RAS) using intra-arterial digital subtraction angiography (IA DSA) as the gold standard.

MATERIALS AND METHODS

This prospective, randomized, double-blind, parallel-group, multicenter study included 273 patients referred to IA DSA for suspected RAS. Patients underwent 3D CE MRA after injection of 0.01, 0.05, 0.1, or 0.2mmol/kg of body weight gadodiamide (0.5mmol/ml). The images were assessed for location and degree of RAS by independent blinded readers (MRA: three readers, IA DSA: one reader). Hypothesis testing for a significant trend in sensitivity across dose groups was based on the one-sided Cochran-Armitage style trend test for each independent MRA reader.

RESULTS

The lowest dose group (0.01mmol/kg) proved non-efficacious in detecting hemodynamically relevant (i.e., > or =50% or occlusion) RAS. A statistically significant dose trend (p<0.001) was shown for each of the three independent readers. Depending on reader, the sensitivity obtained with 0.05, 0.1, and 0.2mmol/kg was 63.9-86.1%, 75.8-91.4% and 80.6-90.6%, the specificity was 66.7-73.9%, 59.3-75.0%, and 59.3-75.0% and accuracy was 67.8-78.9%, 75.4-77.4%, and 76.3-81.0%, for the three dose groups, respectively. There were eight non-severe adverse events (AEs). Three serious AEs occurring in one patient were judged not related to gadodiamide by the on-site investigator.

CONCLUSION

A significant dose trend between the four doses examined was observed. The lowest dose (0.01mmol/kg) differed significantly from those of the other three doses. Based on the analysis of the primary and secondary endpoints, 0.1mmol/kg gadodiamide appears to be the most suitable dose in diagnosing hemodynamically relevant RAS. The present study also demonstrated gadodiamide to be safe and well tolerated.

Time-Efficient Breath-Hold Abdominal MRI at 3.0 T

OBJECTIVE

The purpose of this study was to increase the allowed number of acquired slices per unit time (i.e., time efficiency) for high-power deposition breath-hold abdominal acquisitions at 3.0 T.

MATERIALS AND METHODS

Abdominal MRI protocols include various T1-weighted, T2-weighted, and contrast-enhanced acquisitions that require extended spatial coverage and resolution. Ideally, each acquisition is completed within one breath-hold. At 3.0 T, power deposition (i.e., specific absorption rate [SAR]) concerns can limit achieving these conflicting needs because conventional sequences are based on 6-minute time-average SAR requirements. We optimized abdominal-specific sequences based on an approved short-term 10-second time-average SAR criterion and added a delay time after breath-holding to fulfill the long-term 6-minute time-average power deposition regulation.

RESULTS

Using our strategy, image acquisition time efficiency at 3.0 T was increased approximately twofold compared with conventional abdominal breath-hold pulse sequences for 2D dual-echo gradient-recalled echo, single-shot fast spin-echo, and 3D steady-state free precession sequences. Volunteers experienced a slight sensation of warmth for the single-shot fast spin-echo implementation, the most SAR-intensive sequence.

CONCLUSION

Our optimization strategy is not vendor-specific, is easily implemented for all conventional scanners (provided one can access and modify the pulse sequences directly, or the vendors can make the necessary changes), yields a higher slice-per-unit-time imaging efficiency, and still satisfies all the regulatory power deposition requirements.

Angiografia por ressonância magnética na avaliação das artérias renais: achados de imagem

OBJETIVO: Descrever as indicações, os principais diagnósticos e os achados de imagem nas angiografias por ressonância magnética das artérias renais. MATERIAIS E MÉTODOS: Estudo retrospectivo, no período de 6/12/2001 a 11/3/2004, num total de 56 exames, totalizando 111 artérias renais estudadas. Os exames foram realizados em um equipamento de 1,5 tesla, segundo o protocolo do Serviço. RESULTADOS: Foi demonstrado que 55,4% (n = 31) pacientes eram masculinos e 44,6% (n = 25), femininos. O paciente mais novo tinha 12 anos e o mais velho, 88 anos. De um total de 25 diferentes indicações, a hipertensão arterial sistêmica com 26,7% (n = 15) foi a principal, seguida de dor abdominal e/ou lombar com 12,5% (n = 7), aneurisma da aorta abdominal com 10,7% (n = 6), estenose da artéria renal com 8,9% (n = 5), e outros. No que se refere às imagens, 43 (76,7%) exames tiveram algum tipo de alteração e 13 (23,2%) foram normais. Dentre os que tinham alterações, a maioria se deu no calibre, e dentre elas, as irregularidades parietais, aneurismas e estenoses foram as mais comuns. Na artéria renal direita as alterações mais comuns foram as irregularidades parietais com 17,87% (n = 10), e na artéria renal esquerda foram as estenoses com 25,45% (n = 14). CONCLUSÃO: A angio-RM mostrou-se excelente método no estudo das artérias renais, devido à sua sensibilidade e capacidade multiplanar para avaliar as estruturas vasculares.

Angiographie par résonance magnétique dans les anévrismes et pseudoanévrismes des artères splanchniques

PURPOSE

To correlate Magnetic resonance angiography (MRA) with computed tomography for the diagnosis of splanchnic artery aneurysms.

MATERIALS-METHODS

We retrospectively reviewed the MRA findings of splanchnic arteries performed in 16 patients with known splanchnic aneurysms. Sixteen patients underwent computed tomography (CT), and MRA. Conventional angiogram was performed to confirm the diagnosis in six cases. This study was conducted on a 1.5T MR Symphony system (Siemens, Erlangen, Germany). CE-MRA was performed by using a 3D RF-spoiled FLASH sequence. Acquisition of source images was performed in the coronal plane and reconstructed by means of maximum-intensity projection (MIP) post-processing.

RESULTS

Patient population included 7 men and 9 women aged from 31 to 85 years old (mean age 59.5 years old). Splanchnic aneurysms were located as follows: splenic (n=5), hepatic (n=6), celiac trunk (n=4) and gastroduodenal (n=1). In 9 cases, MRA provided results similar to CT. In 3 cases, MRA provided more accurate information on the location of the aneurysm or detected additional aneurysms. In 4 patients, a diagnosis of aneurysm was made first or only made on MRA.

CONCLUSION

This small series showed a good correlation between CT and MRA for detection and characterization of splanchnic aneurysms.

Role of magnetic resonance imaging in the early diagnosis of Takayasu arteritis

Takayasu arteritis is a non-specific inflammatory process of unknown aetiology affecting the aorta and its major branches. It may lead to stenosis or occlusion. We have examined eight patients with clinically diagnosed Takayasu arteritis using contrast-enhanced MRI and also 3-D MR angiography. All patients were female and their ages varied between 22 and 48 years. We were able to show subtle arteritic changes and stenotic lesions in branch vessels in the early phase of the disease by using this imaging modality. Thus, we can state that contrast-enhanced MRI with 3-D MR angiography can be used for the initial diagnosis of Takayasu arteritis. It provides a means to evaluate the vascular tree non-invasively and may replace conventional angiography.

Contrast-enhanced MR Angiography of the renal arteries: blinded multicenter crossover comparison of gadobenate dimeglumine and gadopentetate dimeglumine

PURPOSE

To prospectively and intraindividually compare 0.1 mmol/kg gadobenate dimeglumine with 0.2 mmol/kg gadopentetate dimeglumine for contrast material-enhanced magnetic resonance (MR) angiography of the renal arteries.

MATERIALS AND METHODS

Institutional review board approval was granted by each of three participating centers. The study accorded with international standards for good clinical practice and Declaration of Helsinki and subsequent amendments. Patients gave written informed consent before enrollment. Patients (n = 34) underwent two MR angiographic examinations more than 48 hours but less than 12 days apart. Gadobenate dimeglumine followed by gadopentetate dimeglumine was administered in 18 patients; the order of administration was reversed in 16 patients. A 1.5-T MR imager was used with a phase-encoded three-dimensional spoiled breath-hold pulse sequence. Two blinded independent readers qualitatively assessed randomized subtracted maximum intensity projection images. A three-point scale for diagnostic quality (0, poor; 1a or 1p, moderate; and 2a or 2p, adequate [a and p refer, respectively, to absence and presence of vascular lesions]) was used to score each of nine segments of the abdominal aorta and both renal arteries (possible overall score, 18). Quantitative assessment (vessel signal-to-noise ratio [SNR], vessel-muscle contrast-to-noise ratio [CNR]) of source images was performed for regions of interest in supra-, juxta-, and infrarenal aorta segments and psoas muscle. Data were tested with analysis of variance for two-period crossover design. Interreader agreement was evaluated with Cohen kappa statistics.

RESULTS

No difference in mean image quality between the two contrast agents was observed; scores for gadobenate dimeglumine and gadopentetate dimeglumine were 15.15 and 15.23 for reader 1 and 16.77 and 17.01 for reader 2. The order of contrast material administration likewise produced no quality differences: readers 1 and 2 reported scores of 14.4 +/- 4.2 (standard deviation) and 16.7 +/- 2.3, respectively, when gadobenate dimeglumine was given first, and 15.2 +/- 1.8 and 16.6 +/- 1.6, respectively, when gadopentetate dimeglumine was given first. Results of quantitative evaluation showed increasing SNR and CNR with gadobenate dimeglumine in segments at progressively lower levels of the aorta, but increases in SNR and CNR at the infrarenal aorta (48.3 vs 40.6 and 44.2 vs 36.4, respectively) were not significant (P = .05 for both).

CONCLUSION

Gadobenate dimeglumine at a dose of 0.1 mmol/kg is comparable to gadopentetate dimeglumine at 0.2 mmol/kg for contrast-enhanced renal MR angiography.

Renal MR angiography

The high accuracy of renal MR angiography makes it well suited for diagnosing renal vascular disease. A comprehensive examination includes three-dimensional gadolinium MR angiography to assess lumenal anatomy and functional techniques to assess the hemodynamic significance of any stenosis identified. Postprocessing is critical to provide reformations, maximum intensity projections, and optional volume-rendered images to display arteries in an angiographic format for optimal demonstration of any vascular lesions. It is important to review source images to avoid missing pathologic findings. As MR imaging continues to develop, the renal MR angiography examination will likely expand to include extensive functional information about creatinine clearance, flow, and response to pharmacologic agents as well as spectroscopy, diffusion, perfusion, phase contrast, and other techniques.

MRA versus DSA in the assessment of occlusive disease in the aortic arch vessels: accuracy in detecting the severity, number, and length of stenoses

PURPOSE

To compare the diagnostic accuracy of contrast-enhanced magnetic resonance angiography (MRA) to that of digital subtraction angiography (DSA) in the detection, grading, and measurement of atherosclerotic stenoses involving the aortic arch arteries.

METHODS

The MRA and DSA studies from 28 patients (16 women; mean age 61.6 years, range 24-83) being evaluated for possible aortic arch vessel disease were examined. The aortic arch vasculature was divided into 9 segments; within each segment, the presence and severity of stenotic or occlusive disease was determined based on a 5-point scale. In addition, stenosis length and distance to the branch were measured in 5-mm increments. Image quality was assessed using a 5-point scale. The accuracy, sensitivity, and specificity values, as well as the positive and negative predictive values in MRA's identification of lesions, were evaluated in comparison to DSA.

RESULTS

In 28 patients, 189 segments were assessed by both methods. Of these, 173 were correctly rated by MRA, resulting in an accuracy of 91.5%. The accuracy dropped slightly to 86.5% when 11 "not assessable" lesions were included. Sensitivity and specificity for severity measurement were 88.5% and 95.6%, respectively. In 39 of 45 lesions, stenosis length measurements were identical by both methods, but there was a difference of 0.5 cm each in 6 lesions.

CONCLUSIONS

MRA as compared to DSA shows high accuracy in the detection and grading of lesions involving the aortic arch vessels. The noninvasive nature of this method recommends its use for screening, treatment planning, and follow-up in known or suspected arterial disease in aortic arch arteries.

Role of MRI in clinical cardiology

Rapid progress has been made in cardiac MRI (CMRI) over the past decade, which has firmly established it as a reliable and clinically important technique for assessment of cardiac structure, function, perfusion, and myocardial viability. Its versatility and accuracy is unmatched by any other individual imaging modality. CMRI is non-invasive and has high spatial resolution and avoids use of potentially nephrotoxic contrast agent or radiation. It has been extensively studied against other established non-invasive imaging modalities and has been shown to be superior in many scenarios, particularly with respect to assessment of cardiac and great vessel morphology and left ventricular function. Furthermore, its clinical use continues to expand with increasing experience and proliferation of CMRI centres. As worldwide prevalence of cardiovascular disease continues to rise, CMRI provides opportunity for improved and cost-effective non-invasive assessment. Continued progress in CMRI technology promises to further widen its clinical application in coronary imaging, myocardial perfusion, comprehensive assessment of valves, and plaque characterisation.

Quand, comment et pourquoi réaliser une exploration des artères rénales ?

The objectives of this course are both: to describe acquisition, injection and reconstruction parameters of volumic images for renal arteries examination and specific signs; to discuss the role of the different images in the diagnosis and in the therapeutic management. Ultrasound is one of the best imaging for the analysis of renal arteries in the detection of stenosis even if the sensitivity is less (around 85%)compared to CT Angiography (95%) and MR Angiography (90%). Because of this advantage and of 3D evaluation, CTA and MRA are sometimes in the first line for renal artery evaluation and can assess morphology before angioplasty. Renal scintigraphy with Captopril test and renin dosage are only used for small kidney evaluation. Arteriogram is systematically followed by angioplasty if possible. With the new endovascular materials, complications decrease (less than 5% with a major reduction in cholesterol emboli) and indications of endoprosthesis increase (71% of stenting with half of it in direct stenting technique). This course will give practical tools for imaging acquisition, specifically 3D imaging, for indications and management of lesion in accordance to symptoms and morphology.

Congenital familial vascular anomalies: a study of patients with an anomalous inferior vena cava, and of their first-degree relatives

With magnetic resonance angiography and computed tomography, congenital anomalies of the inferior vena cava are diagnosed more frequently than they used to be. Accessory renal arteries identified by magnetic resonance angiography in a patient with an anomalous inferior vena cava indicated a combination of arterial and venous abnormalities. The study was initiated to screen consecutive patients with an anomalous inferior vena cava for concomitant abdominal and pelvic arterial abnormalities, and their first-degree relatives for congenital vascular anomalies. Magnetic resonance angiography identified in 2 of 5 patients with an anomalous inferior vena cava concomitant accessory renal arteries and in 5 of 11 first-degree relatives major abdominal vascular anomalies including accessory renal arteries, accessory renal veins, and anomalies of the hepatic artery. None of the relatives showed abnormalities of the inferior vena cava. The familial occurrence of vascular anomalies strongly suggests an underlying pathogenetic component in affected family members. In patients with a congenital anomaly of the inferior vena cava, concomitant arterial abnormalities should be considered. First-degree relatives may be at risk for congenital vascular anomalies.

Cardiovascular shunts: MR imaging evaluation

Magnetic resonance (MR) imaging has become an important tool for the accurate and noninvasive assessment of congenital heart disease. Because more precise delineation of anatomy and evaluation of function can be obtained with MR imaging than with either echocardiography or angiography, MR imaging is frequently used to evaluate cardiovascular shunt lesions. It is essential that imaging specialists be able to recognize the MR imaging features of various kinds of shunts, including supracristal ventricular septal defect, atrioventricular septal defect, and partial anomalous pulmonary venous connection. MR imaging is particularly useful for evaluating shunt severity, which can be expressed quantitatively as the ratio of pulmonary flow to systemic flow. This ratio can be estimated accurately with the use of either volumetric cine MR imaging or velocity-encoded cine MR imaging.

[Duration of enhancement and scan timing in three-dimensional contrast-enhanced MR angiography using the elliptical centric phase-encoding technique]

In the present study, we quantitatively investigated the relationship between the signal intensity in a vessel and the duration of contrast enhancement as well as scan timing in 3D contrast-enhanced MR angiography using an elliptical centric phase-encoding technique. A tube phantom filled with Gd-DTPA, acting as a vessel, was taken out from the field of view during data acquisition, by using the "pause" function of our MR scanner (GE Signa, 1.5 Tesla), thereby simulating the presence and absence of a vessel. The shortening of the duration of enhancement corresponds to the delay of scan timing from the optimal point in the phase-encoding of the centric-ordering system. The signal intensity in a vessel (1-5 mm in diameter) decreased as the duration of enhancement became shorter and the diameter of the vessel decreased. When the number of partitions was 16 or 32 in a 128-mm-thick slab, the signal intensity obtained by the elliptical centric phase-encoding technique was almost the same as that obtained by the conventional centric phase-encoding technique. However, when the number of partitions was increased (64-124), and if the duration of enhancement was short, the signal intensity obtained by the elliptical centric phase-encoding technique was higher than that obtained by the conventional centric phase-encoding technique. In conclusion, in terms of the duration of enhancement and the delay of scan timing, the elliptical centric phase-encoding technique is superior to the conventional centric phase-encoding technique when the number of partitions in a slab for 3D MR angiography is increased.

Safety of contrast-enhanced MR angiography employing gadobutrol 1.0 M as contrast material

Our objectives were to evaluate the safety of intravenous 1.0-M gadobutrol injections in patients with an indication for contrast-enhanced magnetic resonance angiography (CE MRA) of supra-aortal, pelvic, or peripheral arteries by examining and assessing adverse events, laboratory values, vital signs and ECG findings for clinical significance. In 435 patients, recruited in three multicenter trials for safety evaluations of the new contrast agent 1.0-M gadobutrol, CE MRA was performed with 1.0- to 1.5-T scanners using three-dimensional gradient-echo sequences and phased-array coils. The study population comprised 312 men and 123 women with a mean age of 60.9 years. Two hundred seven patients had an indication for imaging of body arteries and 228 had an indication for imaging of peripheral arteries. Blood laboratory values and urinalysis results of 124 patients as well as heart rate, blood pressure, and 12-lead-electrocardiogram readings of 93 patients obtained during a follow-up period of up to 72 h after the injection of contrast media were available for safety analysis. Contrast media application was performed as intravenous bolus injection of 1.0-M gadobutrol in fixed doses according to the patients' body weight (b.w.) and indication for CE MRA and was followed by a 20- to 40-ml saline flush. Mean dose actually applied was 0.1 0.27 mmol/kg b.w. Flow rate ranged between 0.2 and 2.0 ml/s. Safety evaluations found a good tolerability with only 4.6% of at least "possibly related" adverse reactions and no clinically relevant changes in blood and urine samples including no transmetallation effect on serum zinc values. Analysis of renal tolerance showed no influence on renal function irrespective of preexisting renal impairment. The ECG analysis (rhythm analysis, pace-setting disturbances, conduction disturbances, and time interval measurements, including uncorrected and corrected QT) showed no clinically relevant effect of the injection of 1.0-M gadobutrol on the cardiac conduction system. Intravenous injection of 1.0-M gadobutrol at a dose of up to 0.1 0.27 mmol/kg b.w. in the indication CE MRA is safe and causes no clinically relevant changes in safety parameters such as heart rate, blood pressure, blood and urine laboratory values, and cardiac conduction system.

Simultaneous magnetic resonance gadolinium-enhanced 2D perfusion and 3D angiographic imaging

A method was implemented and tested that allows the simultaneous acquisition of magnetic resonance 2D slice selective perfusion and 3D angiographic data during a single bolus injection of a contrast agent. High quality contrast-enhanced perfusion images and angiograms of the lung, kidney and heart were obtained in healthy volunteers. Combined perfusion and angiography provided additional information with an acceptable increase in acquisition time. No image artifacts were attributed to the technique. The combined information may be useful in detecting, as well as characterizing, vascular abnormalities.

Comparison of high-resolution contrast-enhanced 3D MRA with digital subtraction angiography in the evaluation of hepatic arterial anatomy

AIM

To evaluate the validity of high-resolution contrast-enhanced three-dimensional magnetic resonance angiography (MRA) in defining hepatic arterial anatomy and to compare this with digital subtraction angiography (DSA).

MATERIALS AND METHODS

MRA and DSA were performed in 30 patients. MRA was performed with breath-hold, gadolinium-enhanced, three-dimensional, fast low-angle shot sequence with a 512 pixel matrix. MRA was compared with DSA in terms of image quality and depiction of hepatic arterial anatomy. The agreement in image quality between MRA and DSA was determined with the kappa statistic.

RESULTS

With respect to image quality, there was excellent or good correlation between MRA and DSA for the common hepatic artery (kappa=0.85), proper hepatic artery (kappa=0.72), gastroduodenal artery (kappa=0.70), left hepatic artery (kappa=0.49), left gastric artery (kappa=0.50), splenic artery (kappa=0.84), and superior mesenteric artery (kappa=0.88). Poor correlation was found for the right hepatic artery (kappa=0.18) and right gastric artery (kappa=0.38). With regard to hepatic arterial anatomy, MRA correlated correctly with DSA in 28 of the 29 cases, i.e. 97% of patients.

CONCLUSION

MRA is a useful technique for the evaluation of the hepatic artery, and for the vast majority of patients, MRA can replace intra-arterial DSA.

The diagnosis and management of renovascular disease: a primary care perspective. Part I. Making the diagnosis

Renovascular disease is a complex disorder, the most common causes of which are fibromuscular dysplasia and atherosclerotic disease. It usually presents in one of three forms: asymptomatic renal artery stenosis, renovascular hypertension, or ischemic nephropathy. This complexity often makes diagnostic and management decisions difficult. This review will be presented in two parts. In Part I, the authors will discuss when to consider and how to go about making the diagnosis. In Part II (in a future issue of The JCH), the authors discuss the management of renovascular disease. The clinical index of suspicion remains paramount in setting the diagnostic strategy. Although it is subject to certain limitations, conventional contrast angiography is usually considered the gold standard in confirming the diagnosis. In addition, there are a number of available noninvasive tests that can aid in decision making. These tests can be divided into those that detect the anatomic presence of a stenosis and those that identify the functional consequences of the renal artery obstruction. No one study is appropriate for every patient. A diagnostic algorithm is proposed at the conclusion of this review.

Preoperative evaluation of the entire hepatic vasculature in living liver donors with use of contrast-enhanced MR angiography and true fast imaging with steady-state precession

PURPOSE

To preoperatively assess the entire hepatic vasculature in living related liver donors with use of a combination of contrast material-enhanced magnetic resonance (MR) angiography and true fast imaging with steady-state precession (FISP).

MATERIALS AND METHODS

Twenty-five living potential liver donors were examined preoperatively on a 1.5T Siemens Sonata system. Twenty-four underwent surgery and two had catheter angiography performed to delineate complex anatomy. Contiguous 5-mm-thick, sub-second true FISP images of the liver were initially obtained during breath-holding in axial and coronal planes (repetition time [TR]/echo time [TE], 3.2/1.6; flip angle, 70 degrees ). MR angiography was performed with use of a three-dimensional (3D) gradient-echo fast low-angle shot (FLASH) pulse sequence (TR/TE, 3.0/1.2; flip angle, 25 degrees ), with 40 mL of Gadolinium DTPA injected at a rate of 2 mL/sec. One precontrast and two postcontrast coronal 3D volumes were acquired, each in a 20-second breath-hold, and two subtracted 3D sets were calculated. Arterial anatomy was assessed with use of maximum-intensity projection, volume rendering, and multiplanar reformatting algorithms. Hepatic and portal venous anatomy was evaluated with use of the true FISP images and the venous phase of the MR angiogram. Visualization of hepatic arterial branches was noted. Visualization of portal vein branches was scored on a scale of 0-5. The presence of anatomic variants was noted. Vascular anatomy was confirmed at the time of surgery and at catheter angiography.

RESULTS

Segmental branch vessels were visualized on MR angiography in the majority of cases. The segment four branch was identified in 96% patients. Variant arterial anatomy was seen in 50% of patients. MR angiography detected 10 of 11 arterial variants found at surgery and angiography. Visualization of portal vein branches was generally higher with true FISP compared to MR angiography. Twenty-four percent of patients had variant portal venous anatomy. Caudal hepatic veins were identified in 60% of patients, of which eight were significant (>5 mm). Hepatic and portal venous anatomy was accurately predicted by true FISP and MR angiography in all patients who went on to undergo surgery.

CONCLUSION

Preoperative imaging with use of a combination of contrast-enhanced MR angiography and true FISP provides a comprehensive assessment of the entire hepatic vasculature in living liver donors.

Bolus-chasing contrast-enhanced 3D MRA of the lower extremity. Comparison with intraarterial DSA

PURPOSE

To evaluate step-table 3D contrast-enhanced (CE) MRA with bolus chasing for the detection and grading of stenoses in patients with peripheral vascular disease (PVD) of the lower extremities.

MATERIAL AND METHODS

Fifty patients were studied by step-table bolus-chasing 3D-CE-MRA and i.a. DSA within 24 h. After determination of the individual circulation time, CE-MRA was performed during power injection of 40 ml of Gd-DTPA. To cover the whole range between the renal arteries and the feet with three slab locations, the scanner table was manually advanced twice for 350 mm. Total imaging time was 1 min 23 s. The degree of stenosis and image quality of the images were evaluated by 2 observers. In addition, a treatment plan was established based on the 3D-CE-MRA and DSA investigations.

RESULTS

In 44 of 50 patients (88%), the visualization of the arterial tree from the renal arteries to the foot was possible. Forty-six of 50 patients (92%) had good or very good image quality. In the calf, 3D-CE-MRA was superior to DSA in 6 patients. For the detection of stenosis >50%, sensitivity was 99.5%, specificity 98.8%, positive predictive value 95.6% and the negative predictive value 99.8%. Cohen's kappa for 3D-CE-MRA vs. DSA was 0.926; for interobserver agreement it was 0.96.

CONCLUSION

Bolus-chasing 3D-CE-MRA with manual table movement is a simple, robust and easy to perform technique which provides high quality angiograms of the lower extremity arterial system and is comparable to, i.a., DSA for the diagnosis of PVD.

Splanchnic blood flow determination in patients with suspected chronic intestinal ischaemia

Chronic intestinal ischaemia is characterized by postprandial abdominal pain and prominent weight loss, often leading to the first clinical suspicion of malignancy. After ruling out various gastrointestinal disorders, chronic intestinal ischaemia should be considered as a potential diagnosis. Besides the clinical picture, various non-invasive procedures are helpful in establishing the diagnosis. Whereas a plain abdominal radiography may show arterial calcifications, duplex ultrasonography is nowadays the leading diagnostic procedure for ruling out significant disease. Another promising and increasingly used technology is magnetic resonance angiography. Suspicious findings must be followed by the gold standard in diagnosis, namely splanchnic angiography. Since all these technologies provide only anatomical evidence of disease, functional imaging techniques assessing splanchnic blood flow after meal challenge using the invasive indocyanine green method may be helpful. However, further studies are needed in the use of this experimental technique in the workup of these patients.

Mesenteric arterial occlusive and aneurysmal disease

Mesenteric arterial diseases are a heterogeneic group of clinically significant illnesses that have become recognized with increasing frequency because of the more common imaging of the intestinal circulation when studying both vascular and nonvascular diseases of the abdomen. Considerable knowledge exists regarding some of these diseases, whereas the understanding of others is anecdotal. It is important for clinicians to recognize differences among common ischemic diseases and common splanchnic aneurysms.

Value of MR angiography before percutaneous transluminal renal artery angioplasty and stent placement

PURPOSE

To determine the benefit of preprocedural three-dimensional gadolinium (Gd)-enhanced magnetic resonance (MR) angiography before percutaneous transluminal renal artery angioplasty and stent placement (PTRA/S) in terms of procedural success, iodinated contrast material load, and procedure duration.

MATERIALS AND METHODS

Over an 18-month period, 39 patients underwent attempted percutaneous renal angioplasty with or without stent placement. A total of 48 renal arteries were treated (40 cases of atherosclerosis, one of stent restenosis, five of fibromuscular dysplasia, and two of transplant stenosis). Preprocedural Gd-enhanced MR angiography was available in 16 procedures (41%). Procedural outcome, complications, iodinated contrast material load, number of diagnostic angiographic runs, and total procedure duration were each compared between two subgroups: patients who had preprocedural Gd-enhanced MR angiography ("prior MR angiography group") and those who did not ("no MR angiography" group).

RESULTS

All procedures were technically successful. The two groups were equivalent in terms of age and disease pattern. However, technical complexity of the procedure was judged to be high in five of 16 procedures in the prior MR angiography group compared to three of 23 procedures in the no MR angiography group (P =.16). Bilateral or dual interventions were performed in six of 16 procedures in the prior MR angiography group compared to three of 23 in the no MR angiography group (P =.075). Iodinated contrast material load was significantly lower in the prior MR angiography group than in the no MR angiography group (68.7 mL +/- 28.4 vs 119.1 mL +/- 49.2 mL;P <.0008). The number of diagnostic angiographic runs before interventions were also significantly lower in the prior MR angiography group (1.2 +/- 0.4 vs 2.6 +/- 0.7; P <.0001). Overall procedure duration was comparable between the two groups (91.9 +/- 47.8 vs 112.2 +/- 49.4;P =.2).

CONCLUSION

Preprocedural planning with use of Gd-enhanced MR angiography significantly reduces the iodinated contrast material requirement during percutaneous renal artery interventions. It can also significantly shorten procedure duration.

MR angiography of the renal arteries

During, the past decade. MRA has evolved from an cxperimental technique into the modality of choice for the noninvasive evaluation of renovascular disease. The recent widespread application of MRA for these indications has been driven primarily by the advent of 3D contrast-enhanced MRA. which provides a fast, reliable technique for imaging large vascular territories and generates images, after postprocessing, similar in appearance to digital subtraction angiography. The cross-sectional volumetric nature of contrast-enhanced MRA affords some advantages over conventional catheter angiography. Although 3D contrast-enhanced MRA forms the backbone of vascular MR studies, several adjunctive sequences are employed to maximize the diagnostic yield of the examination. For example. flow-dependant imaging is used to complement the morphologic images of contrast-enhanced MRA by providing hemodynamic information. As such, MRA is unique among noninvasive imaging modalities in that it offers a comprehensive evaluation of anatomy and function. The availability and reliability of MRA extend renal artery screening to a wider spectrum of patients. Current applications of renal MRA range from detection of renal artery stenosis to evaluation for renal transplant donors.

Magnetic resonance angiography for the diagnosis of renal artery stenosis: a meta-analysis

AIM

To review the published literature comparing the diagnostic accuracy of magnetic resonance angiography (MRA) with and without gadolinium in diagnosing renal artery stenosis, using catheter angiography as reference.

MATERIALS AND METHODS

A meta-analysis was performed of English language articles identified by computer search using PubMed/MEDLINE, followed by extensive bibliography review from 1985 to May 2001. Inclusion criteria were: (1) blinded comparison with catheter angiography; (2)indication for MRA stated; (3) clear descriptions of imaging techniques; and (4) interval between MRA and catheter angiography < 3 months and only the largest of all studies from one centre was selected in the analysis.

RESULTS

A total of 39 studies were identified, of which 25 met the inclusion criteria. The number of patients included in the meta-analysis was 998: 499 with non-enhanced MRA and 499 with gadolinium-enhanced MRA. The sensitivity and specificity of non-enhanced MRA were 94% (95% CI: 90-97%) and 85% (95% CI: 82-87%), respectively. For gadolinium-enhanced MRA sensitivity was 97% (95% CI: 93-98%) and specificity was 93% (95% CI: 91-95%). Thus, specificity and positive predictive value were significantly better for gadolinium-enhanced MRA (P < 0.001). Accessory renal arteries were depicted better by gadolinium-enhanced MRA (82%; 95% CI: 75-87%) than non-gadolinium MRA (49%; 95% CI: 42-60%) (P < 0.001).

CONCLUSIONS

Gadolinium-enhanced MRA may replace arteriography in most patients with suspected renal artery stenosis, and has major advantages in that it is non-invasive, avoids ionizing radiation and uses a non-nephrotoxic contrast agent.

Noninvasive assessment of portomesenteric venous thrombosis: current concepts and imaging strategies

Rapid, noninvasive imaging strategies, especially multidetector spiral CT and CT angiography (CTA) as well as gadolinium-enhanced MR angiography (MRA), have facilitated early diagnosis of splanchnic venous thrombosis, a potentially lethal cause of intestinal ischemia. Single breath-hold volumetric acquisitions permit superior temporal and contrast resolution while eliminating motion artifact and suppressing respiratory misregistration. Increased spatial resolution is aided by thinner slice collimation. These cross-sectional imaging techniques are becoming a preferred noninvasive alternative to conventional selective mesenteric angiography with delayed imaging for venous evaluation and should be considered the primary diagnostic modalities for evaluating patients with high clinical suspicion of nonsurgical mesenteric ischemia.

[Simulation study of scan timing in three-dimensional contrast-enhanced MR angiography]

In our study of three-dimensional contrast-enhanced MR angiography, we performed a computer simulation to quantitatively investigate vessel visibility according to scan timing. To construct the simulated MR images, we varied the position (scan timing) and range (enhancement-duration) of k-space data assumed to be acquired during contrast enhancement. In the present study, either the sequential or centric phase-encoding order in k(y) and k(z) on k-space was assumed to be used. When scan timing was shifted from the optimal timing, the visibility of thick vessels decreased, and the signal intensity in thin vessels was higher than that in thick vessels. We found that the appropriate setting of scan timing was an important factor in the visibility of thick vessels. Meanwhile, we also noted that extending the enhancement-duration (or shortening the scan time) could increase the visibility of thin vessels. Our results and the simple technique used for simulation are considered to be useful for the study of three-dimensional contrast-enhanced MR angiography.

Mesenteric venous thrombosis: diagnosis and noninvasive imaging

Mesenteric venous thrombosis is an uncommon but potentially lethal cause of bowel ischemia. Several imaging methods are available for diagnosis, each of which has advantages and disadvantages. Doppler ultrasonography allows direct evaluation of the mesenteric and portal veins, provides semiquantitative flow information, and allows Doppler waveform analysis of the visceral vessels; however, it is operator dependent and is often limited by overlying bowel gas. Conventional contrast material-enhanced computed tomography (CT) allows sensitive detection of venous thrombosis within the central large vessels of the portomesenteric circulation and any associated secondary findings; however, it is limited by respiratory misregistration, motion artifact, and substantially decreased longitudinal spatial resolution. Helical CT and CT angiography, especially when performed with multi-detector row scanners, and magnetic resonance (MR) imaging, particularly gadolinium-enhanced MR angiography, enable volumetric acquisitions in a single breath hold, eliminating motion artifact and suppressing respiratory misregistration. Helical CT angiography and three-dimensional gadolinium-enhanced MR angiography should be considered the primary diagnostic modalities for patients with a high clinical suspicion of mesenteric ischemia. Conventional angiography is reserved for equivocal cases at noninvasive imaging and is also used in conjunction with transcatheter therapeutic techniques in management of symptomatic portal and mesenteric venous thrombosis.