Joerg F. Debatin

MR-Guided Percutaneous Angioplasty: Assessment of Tracking Safety, Catheter Handling and Functionality

AbstractPurpose: Magnetic resonance (MR)-guided percutaneous vascular interventions have evolved to a practical possibility with the advent of open-configuration MR systems and real-time tracking techniques. The purpose of this study was to assess an MR-tracking percutaneous transluminal angioplasty (PTA) catheter with regard to its safety profile and functionality. Methods: Real-time, biplanar tracking of the PTA catheter was made possible by incorporating a small radiofrequency (RF) coil in the catheter tip and connecting it to a coaxial cable embedded in the catheter wall. To evaluate potentially hazardous thermal effects due to the incorporation of the coil, temperature measurements were performed within and around the coil under various canning and tracking conditions at 1.5 Tesla (T). Catheter force transmission and balloon-burst pressure of the MR-tracking PTA catheter were compared with those of a standard PTA catheter. The dilatative capability of the angioplasty balloon was assessed in vitro as well as in vivo, in an isolated femoral artery segment in a swine. Results: The degree of heating at the RF coil was directly proportional to the power of the RF pulses. Heating was negligible with MR tracking, conventional spin-echo and low-flip gradient-echo sequences. Sequences with higher duty cycles, such as fast spin echo, produced harmful heating effects. Force transmission of the MR-tracking PTA catheter was slightly inferior to that of the standard PTA catheter, while balloon-burst pressures were similar to those of conventional catheters. The MR-tracking PTA catheter functioned well both in vitro and in vivo. Conclusion: The in vivo use of an MR-tracking PTA catheter is safe under most scanning conditions.

MR colonography: How does air compare to water for colonic distention?

To prove the feasibility of air‐distended magnetic resonance colonography (MRC) and compare it with water‐based distention.

Inductively coupled stent antennas in MRI

The development of intimal hyperplasia following stent deployment can lead to narrowing or even occlusion of the stent lumen. The underlying mechanisms leading to neointimal proliferation within stents remain largely unknown. Long‐term evaluation of stent patency requires a noninvasive means for assessing the stent lumen. MR angiography (MRA) has shown potential to provide noninvasive assessment of the vascular system. However, a detailed assessment of the stent lumen with MRI is often hampered by material‐dependent susceptibility artifacts, as well as by radiofrequency (RF) eddy currents generated inside the electrically conducting stent mesh. In this study, stent prototypes were designed to act as active resonant structures at the Larmor frequency of the MR system. Employing the principle of inductive coupling, the B1 fields of the stents were coupled to that of an outside surface coil. The stents thus acted as local RF signal amplifiers. Various stent designs were investigated regarding their coupling to an external coil, signal homogeneity, and suitability for mechanical expansion for implantation purposes. The dependency of flip angle amplification on the quality factor Q of the stents was systematically investigated. Phantom experiments revealed signal amplification in all stent prototypes. Signal enhancement inside and close to the surface of the stents enabled their localization with high contrast in MR images. In vivo imaging experiments in the iliac, renal, and splenic arteries of two pigs confirmed the in vitro findings. Wireless active visualization of stents allows for detailed analysis of the stent lumen with high contrast and spatial resolution. The proposed method could thus provide a powerful diagnostic means for the noninvasive long‐term follow‐up of stent patency, thereby enhancing our understanding of the mechanisms of restenosis. Magn Reson Med 48:781–790, 2002.

Real-time MRI of joint movement with trueFISP

To develop a technique for dynamic magnetic resonance imaging (MRI) of joint motion based on a combination of real‐time TrueFISP (fast imaging with steady state precession) imaging with surface radiofrequency (RF) coils.

Real‐time high‐resolution MRI for the assessment of gastric motility: Pre‐ and postpharmacological stimuli

To determine the practicality of MRI using a new real‐time sequence for the assessment of gastric motion, and quantify the effects of motility‐modifying substances.

In vitro image characteristics of an abdominal aortic stent graft: CTA versus 3D MRA

Percutaneous stent-grafting is increasingly employed as a less invasive alternative to surgery for the treatment of infrarenal abdominal aortic aneurysms. It requires long-term imaging follow-up, to document the structural integrity of the device, to exculude perigraft channels and endograft leakages, as well as the shrinkage of the aneurysmal sac. The expectation of severe stent induced artifacts and safety concerns have prevented 3D MRA from being used. The purpose of this in vitro study was to investigate the imaging characteristics of a bifurcated stent graft with 3D MRA (3D Frourier transform fast spoiled GRE) at 1.5 T in comparison to those of CTA. Measurement of the stent wall thickness and luminal diameter were made on a agar gel embedded stent graft at five locations on both CTA and MRA images. The stent graft was depicted as a dark ring on MR images. Wall thickness measurments at the five locations of the stent graft overestimated the true stent thickness, while luminal diameters were slightly underestimated. Measurement differences between MR and CT were not statistically significant (P=0.67;P=0.85). Artifacts emanating from the platinum markers were considerably less severe on the MR-images. A wider area of signal loss was seen only at the insertion of the iliac stent leg into the aortic stent portion due to the overlap of two radio-opaque platinum markers. 3D MRA images should permit a comprehensive assessment of the arterial lumen, and of perivascular tissues.

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

Impact of Diet on Stool Signal in Dark Lumen Magnetic Resonance Colonography

To examine the magnetic resonance (MR) properties of different foods and their effect on the colonic stool signal to potentially support fecal tagging strategies for dark lumen MR colonography (MRC).

Pulmonary hemorrhage: Imaging with a new magnetic resonance blood pool agent in conjunction with breathheld three-dimensional magnetic resonance angiography

AbstractPurpose: To describe the three-dimensional magnetic resonance angiography (3D MRA) imaging appearance of the pulmonary arteries following administration of a superparamagnetic iron oxide blood pool agent to human volunteers, and to demonstrate in an animal model (pigs) how this technique can be used to detect pulmonary parenchymal hemorrhage. Methods: Two volunteers were examined following the intravenous administration of a superparamagnetic iron oxide blood pool agent (NC100150 Injection, Nycomed Amersham Imaging, Wayne, PA, USA). T1-weighted 3D gradient recalled echo (GRE) image sets (TR/TE 5.1/1.4 msec, flip angle 30°) were acquired breathheld over 24 sec. To assess the detectability of pulmonary bleeding with intravascular MR contrast, pulmonary parenchymal injuries were created in two animals under general anesthesia, and fast T1-weighted 3D GRE image sets collected before and after the injury. Results: Administration of the intravascular contrast in the two volunteers resulted in selective enhancement of the pulmonary vasculature permitting complete visualization and excellent delineation of central, segmental, and subsegmental arteries. Following iatrogenic injury in the two animals, pulmonary hemorrhage was readily detected on the 3D image sets. Conclusion: The data presented illustrate that ultrafast 3D GRE MR imaging in conjunction with an intravenously administered intravascular blood pool agent can be used to perform high-quality pulmonary MRA as well as to detect pulmonary hemorrhage.

Images in vascular medicine Diagnosis of giant cell arteritis with PET/CT

cA 62-year-old male patient presented with persisting weariness of the left arm. Apart from a coronary artery bypass procedure 3 years before, his clinical history was unremarkable. Blood tests revealed an increase of the erythrocyte sedimentation rate (ESR) to 60 in the second hour, while antibodies for rheumatic disease as well as antibodies for collagenous and vasculitic disorders were found to be negative. Fever and myalgic symptoms were not present. Angiography demonstrated multiple vascular stenoses in the right axillary arteries (Panel A), the brachiocephalic trunk (Panel B, arrow), and the left subclavian and axillary arteries (Panel C). Sonographic investigation showed no arteriosclerotic lesions, but irregular wall thickening with poor echogenicity was detected. Based on the patient’ s age, the increased ESR and the location of stenoses, giant cell arteritis was suspected. Clinically, the temporal arteries were not involved, and thus histological evaluation was not expected to be of diagnostic value. To prove the suspected diagnosis of giant cell arteritis, detection of ine ammatory alterations in the vascular lesions was desired. Positron emission tomography (PET) imaging provides functional data for detection of infectious foci and ine ammation. Accurate localization of focal tracer uptake is, however, often compromised due to the limited spatial resolution of the PET data (Panel D). For futher evaluation it was, therefore, decided to perform dual-modality positron emission tomography = computed tomography (PET =CT) with [ 18 F]-2e uoro-2-deoxy- D-glucose as a radioactive tracer. By combining anatomy and function, PET =CT was able to detect ine ammatory alterations shown as areas of focally increased glucose metabolism in accurate co-registration with the vascular segments previously described as being stenosed on angiography (arrows in Panel E). The corresponding CT data were found to be unremarkable (Panel F). Immunosuppressive therapy with a corticoid was recommended. Based on the e ndings in this patient, PET =CT imaging may serve as a non-invasive means to detect ine ammed vascular segments in patients suspected of, or diagnosed with giant cell arteritis.