Daniel A. Leung

Acute mesenteric ischemia caused by spontaneous isolated dissection of the superior mesenteric artery: treatment by percutaneous stent placement

Abstract. Spontaneous and isolated dissection of the superior mesenteric artery is a rare and often fatal event which has been successfully treated by surgery in several reported cases. We present a patient with acute mesenteric ischemia due to superior mesenteric artery dissection who was successfully treated by percutaneous endovascular placement of a Wallstent.

Magnetic Resonance Angiography Versus Duplex Sonography for Diagnosing Renovascular Disease

Noninvasive testing for renovascular disease is required to identify patients who may benefit from revascularization procedures without exposing an unnecessary amount of patients to the risks of catheter angiography. All available methods of diagnosing renal artery stenosis have significant limitations. We compared a new technique, contrast-enhanced magnetic resonance angiography, with an established technique, duplex ultrasonography, for the detection of renal artery stenosis using catheter angiography as the standard of reference. Eighty-nine patients with clinically suspected renovascular disease underwent duplex renal scanning and contrast-enhanced magnetic resonance angiography. Sixty of these also underwent catheter angiography. All studies were interpreted for the presence of renal artery stenosis blinded to the results of the other imaging modalities. For detection of hemodynamically significant (>/=60% diameter reduction) main renal artery stenosis, sensitivity and specificity were 90% and 86%, respectively, for magnetic resonance angiography and 81% and 87% for duplex sonography. Most false readings involved differential grading of stenoses detected with all 3 techniques. When patients with fibromuscular dysplasia were excluded from the analysis, the sensitivity of magnetic resonance angiography increased to 97%, with a negative predictive value of 98%. Magnetic resonance angiography detected 96% and duplex 5% of accessory renal arteries seen at catheter angiography. Contrast-enhanced magnetic resonance angiography is a useful technique for diagnosing atherosclerotic renovascular disease. It overcomes the major limitations of duplex renal scanning. However, duplex has the advantage of providing hemodynamic information and appears better suited for the assessment of patients with suspected fibromuscular dysplasia.

CONTRAST-ENHANCED MAGNETIC RESONANCE ANGIOGRAPHY OF THE RENAL ARTERIES : ORIGINAL INVESTIGATION

RATIONALE AND OBJECTIVES The authors determine the value of contrast-enhanced, three-dimensional (3D) magnetic resonance angiography (MRA) in the assessment of the renal arteries in comparison with conventional arteriography (CA). METHODS One hundred three patients (71 m, 32 f) were evaluated with both CA and 3D MRA. The 3D MRA data set consisted of 44 contiguous sections, acquired in apnea (23-28 seconds) using the following parameters: TR/TE 3.9/1.5 milliseconds, flip angle 40 degrees to 50 degrees, 3/4 k-space acquisition. A bolus of 0.3 mmol/kg BW gadolinium-DTPA was administered intravenously, using an automated injector. A test bolus method was used for timing of the bolus relative to the beginning of the data acquisition. Intra-arterial CA was used as the standard of reference in all patients. Separate interpretations of the CA and MRA results were made by two different pairs of radiologists, who were each blinded to the results of the other exam. RESULTS In all, 31 of 33 accessory renal arteries were correctly identified. All 205 main renal arteries were seen with MRA. Of 65 significant stenoses identified on CA, 61 were correctly identified and graded by MRA. Sensitivity and specificity values for the assessment of significant renal arterial lesions were 93% and 90%, respectively. CONCLUSIONS Breath-hold, contrast-enhanced 3D MRA allows for the reliable assessment of renal arterial morphology and pathologic states.

Three-Dimensional Contrast-Enhanced Magnetic Resonance Angiography of the Abdominal Arterial System

Magnetic resonance angiography (MRA) is increasingly being used as a noninvasive imaging modality for the evaluation of vascular disease. The vascular system of the head and neck are particularly amenable to MRA owing to the characteristic laminar blood flow of carotid and intracerebral arteries [1–3]. In contrast, MRA of the body faces many technical challenges such as large imaging volumes, respiratory motion, and pulsatile flow. As a result, MR imaging (MRI) of abdominal vasculature has, to date, mainly been restricted to evaluation of the venous system [4, 5] and the abdominal aorta [6–10]. With advances allowing the additional assessment of aortic branch vessels, MRA has also been advocated as a possible screening method for renovascular disease [11–13]. However, technical difficulties and limited accuracy have prevented its widespread application. Limitations to conventional MRA of the abdomen include saturation effects which complicate differentiation of slow flow from thrombus, turbulence-induced signal loss resulting in overestimation of stenoses, and long imaging times. Recently, a new strategy in MRA has been developed [14, 15] which overcomes many of the problems that degrade conventional MR angiograms. This technique utilizes the T1-shortening effect of a dynamic paramagnetic contrast infusion to achieve vessel contrast. Hence blood signal is no longer flowdependent and images can be acquired in the plane of the vessels of interest. This allows the acquisition of large three-dimensional (3D) volumes in short imaging times and generates images which are similar in appearance to conventional contrast angiography. Though in principle similar to helical computed tomography (CT) angiography, gadolinium-enhanced

Advances in vascular echoplanar imaging

Magnetic resonance (MR) angiography is emerging as an increasingly useful tool for the noninvasive evaluation of the cardiovascular system. Ultrafast echoplanar imaging (EPI) data acquisition strategies are becoming more widely available. When applied to MR angiography, the associated reduction in data collection time allows breathheld acquisitions of entire vascular territories, as well as the exploitation of short-lived flow-enhancing measures. This paper describes technical aspects of EPI, its implementation into vascular imaging sequences, and associated artifacts. This is followed by a discussion of potential EPI MRA applications in the carotid and renal arteries, the portal venous system, and arteries and veins of the lower leg.

3d phase contrast epi mr angiography of the carotid arteries

Objective Our goal was to compare 3D phase contrast (PC) echo planar imaging (EPI) MRA of the carotid and vertebral arteries with conventional 3D PC in volunteers and patients. Materials and Methods The carotid arteries of 12 volunteers were imaged with conventional and EPI 3D PC sequences. The visibility for each of seven carotid and four vertebral segments was qualitatively assessed. Signal intensity and homogeneity determinations were performed on the source images. Three patients with known carotid artery disease were also imaged with the same protocol. Results EPI reduced 3D PC data acquisition time from 459 to 32 s (factor of 15). Both techniques permitted full assessment of the common carotid artery, the bifurcation, as well as the proximal internal carotid artery (ICA), external carotid artery (ECA), and vertebral arteries. Visualization of the distal ICA/ECA and vertebral arteries was inferior with EPI compared with the conventional acquisition. In all patients, lesions as established by X-ray angiography were seen to equal advantage with both techniques. Conclusion EPI 3D PC MRA renders diagnostic images of the proximal carotid system. The considerable reduction in data acquisition time must be weighed against poorer image quality.

Value of contrast-enhanced 3D MR angiography of the renal arteries

SummaryPurpose: To determine the value of gadolinium-enhanced, three-dimensional breathhold Magnetic Resonance Angiography (MRA) in the assessment of the aorta and renal arteries in comparison to conventional arteriography (CA). Patients and methods: 49 patients were evaluated with both CA and 3D MRA. 0.3 mmol/kg BW gadolinium-DTPA was administered intravenously in a bolus, using an automated injector. A test bolus method was used for timing of the bolus and beginning of the data acquisition. The intraarterial CA was used as the gold standard. Results: MRA-based assessment of renal artery stenosis was identical with CA in 31 of 45 stenoses (68.8 %). Sensitivity and specificity for assessment of renal arterial disease by MRA were 84 % and 96 %; for clinically relevant lesions they amounted to 90 % and 98 %. Conclusion: The presented contrast-enhanced 3D MRA technique allows for the reliable assessment of renal arterial morphology and pathology.ZusammenfassungEinleitung: Nierenarterienstenosen unterschiedlicher Genese können zu arterieller Hypertonie sowie im weiteren Verlauf auch zu einem Nierenversagen führen. Es stehen verschiede invasive wie auch nicht-invasive diagnostische Methoden zur Verfügung. Material und Methode: Für die Bestimmung der Wertigkeit der gadoliniumverstärkten 3D-Magnetresonanz-(MR-)Angiographie (3D MRA) wurde in 49 Patienten die 3D-MRA-Technik mit der konventionellen Katheterangiographie (KA) der Nierenarterien (NA) als Standarduntersuchung verglichen. Für die atemangehaltene (23–28 s), kontrastverstärkte 3D MRA wurde paramagnetisches Kontrastmittel (0,3 mmol/kg KG Gd-DTPA) mit einem automatisierten Injektor intravenös im Bolus appliziert. Die zeitliche Abfolge von Kontrastmittelgabe und Datenakquisition wurde mit einem Testbolus bestimmt. Ergebnisse: Die Einteilung der NA-Stenosen in der MRA und KA war bei 31 von 45 Stenosen (68,8 %) konkordant. Für den Nachweis der NA-Läsionen im allgemeinen lag die Sensitivität sowie Spezifität der MRA bei 84 und 96 %, für klinisch relevante Läsionen bei 90 % bzw. 98 %. Schlußbemerkung: Die 3D MRA-Untersuchungstechnik erlaubt eine zuverlässige Beurteilung von Morphologie und Pathologie der Nierenarterien.

Diagnostic Imaging in Liver Transplantation

The advances in solid organ transplantation achieved in the last 2 decades have seen liver transplantation become a realistic treatment option for patients with hepatic failure. Technical improvements, careful patient selection and particularly the use of cyclosporin have elevated survival rates to 83% at 1 year and 75% at 4 years (Starzl et al. 1989a,b). A wide range of acute and chronic hepatic diseases are presently treated by transplantation. Excellent results have been reported in patients with cryptogenic cirrhosis, chronic active autoimmune or viral (hepatitis C virus) hepatitis, alcoholic cirrhosis, inborn metabolic disorders such as hemochromatosis and Wilson’s disease, as well as cholestatic diseases such as primary biliary cirrhosis, sclerosing cholangitis and biliary atresia. Other common indications include postnecrotic cirrhosis, acute liver failure due to viral hepatitis and drugs, as well as Budd-Chiari syndrome.