Vascular stents as RF antennas for intravascular MR guidance and imaging

Quick, Harald H.; Ladd, Mark E.; Nanz, Daniel; Mikołajczyk, Krzysztof; Debatin, Jörg F.

doi:10.1002/(sici)1522-2594(199910)42:4<738::aid-mrm16>3.0.co;2-y

Cited by 46 publications

(30 citation statements)

References 36 publications

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“…38,39 For clinical use, however, the capacitor design must be minimized, and the potential for visualization of in-stent restenosis and plaque close to the stent, despite locally variable signal intensities, remains to be investigated and may depend on the sequence used. MRI stents with a completely invisible metallic alloy allow sequence-independent and easier visualization of in-stent lumen visualization.…”

Section: Discussionmentioning

confidence: 99%

Artifact-Free Coronary Magnetic Resonance Angiography and Coronary Vessel Wall Imaging in the Presence of a New, Metallic, Coronary Magnetic Resonance Imaging Stent

et al. 2005

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Background-Coronary in-stent restenosis cannot be directly assessed by magnetic resonance angiography (MRA) because of the local signal void of currently used stainless steel stents. The aim of this study was to investigate the potential of a new, dedicated, coronary MR imaging (MRI) stent for artifact-free, coronary MRA and in-stent lumen and vessel wall visualization. Methods and Results-Fifteen prototype stents were deployed in coronary arteries of 15 healthy swine and investigated with a double-oblique, navigator-gated, free-breathing, T2-prepared, 3D cartesian gradient-echo sequence; a T2-prepared, 3D spiral gradient-echo sequence; and a T2-prepared, 3D steady-state, free-precession coronary MRA sequence. Furthermore, black-blood vessel wall imaging by a dual-inversion-recovery, turbo spin-echo sequence was performed. Artifacts of the stented vessel segment and signal intensities of the coronary vessel lumen inside and outside the stent were assessed. With all investigated sequences, the vessel lumen and wall could be visualized without artifacts, including the stented vessel segment. No signal intensity alterations inside the stent when compared with the vessel lumen outside the stent were found. Conclusions-The new, coronary MRI stent allows for completely artifact-free coronary MRA and vessel wall imaging.

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Section: Discussionmentioning

confidence: 99%

Artifact-Free Coronary Magnetic Resonance Angiography and Coronary Vessel Wall Imaging in the Presence of a New, Metallic, Coronary Magnetic Resonance Imaging Stent

et al. 2005

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“…where m n (x, y)is a resultant image, A n (x, y) is an averaged image generated by using equation (4), and f n (x, y) is the original ith image. Note that this subtraction technique employs nonlinear processing similar to that used in the CST and that process could improve the SNR for this technique.…”

Section: Averaged Image Subtraction Techniquementioning

confidence: 99%

Microcatheter Tip Enhancement in Fluoroscopy: A Comparison of Techniques

et al. 2006

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We compared three techniques for enhancement of microcatheter tips in fluoroscopic images: conventional subtraction technique (CST); averaged image subtraction technique (AIST), which we have developed; and double average filtering (DAF) technique, which uses nonlinear background estimates. A pulsed fluoroscopic image sequence was obtained as a microcatheter was passed through a carotid phantom that was on top of a head phantom. The carotid phantom was a silicone cylinder containing a simulated vessel with the shape and curvatures of the internal carotid artery. The three techniques were applied to the images of the sequence, then the catheter tip was manually identified in each image, and 100 x 100 pixel images, centered at the indicated microcatheter tip positions, were extracted for the evaluations. The signal-to-noise ratio (SNR) was calculated in each of the extracted images from which the mean value of the SNR and its standard deviation (SD) were calculated for each technique. The mean values and the standard deviations were 4.36 (SD 3.40) for CST, 6.34 (SD 3.62) for AIST, and 3.55 (SD 1.27) for DAF. AIST had a higher SNR compared to CST in almost all frames. Although DAF yielded the smallest mean SNR value, it yielded the best SNR in those frames in which the microcatheter tip did not move between frames. We conclude that AIST provides the best SNR for a moving microcatheter tip and that DAF is optimal for a temporarily stationary microcatheter tip.

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“…[8] and [9], and respecting the additional factors for pulsed MR sequences, this yields For a given homogenous magnetic field strength B 1 and a specific MR sequence, the total power dissipated by the resonator depends only on its quality factor and volume and is proportional to both (P loss ϳ QV Stent ). For a given resonator, the total power loss is dependent only on the sequence and is proportional to the SAR of that sequence because of the common factors c dc , c pwm and (B 1 ) 2 in Eqs.…”

Section: Power Loss Of the Resonatormentioning

confidence: 99%

“…Instead of increasing excitation or preventing eddy currents, stents can be designed as receive coils (9,10) or as tuned and inductively coupled resonators that function as transmit and receive coils (11)(12)(13)(14)(15)(16) to compensate for the Faraday cage effect (Fig. 1).…”

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confidence: 99%

On the heating of inductively coupled resonators (stents) during MRI examinations

Busch

Vollmann²,

Bertsch³

et al. 2005

Magnetic Resonance in Med

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Stents that have been implanted to preserve the results of vascular dilatation are frequently affected by in-stent restenosis, which ideally should be followed up by a noninvasive diagnostic modality. Active MRI stents can enable this kind of follow-up, while normal metallic stents can not. The prototype stents investigated in this study were designed as electric resonating circuits without a direct connection to the MR imager, and function as inductively coupled transmit coils. The model of a long solenoid coil is used to describe the additional power loss caused by such resonators. The theoretically estimated temperature increase is verified by measurements for different resonators and discussed for worstcase conditions. The RF power absorption of an active resonator is negligible compared to the total power absorbed during MRI. The local temperature increase observed for prototypes embedded in phantoms is in a range that excludes direct tissue damage. However, ruptures in the conducting structure of a resonator can cause hot spots, which may establish a high local temperature. This hazard can be reduced by designing resonators with a low quality (Q) factor or by setting the circuit slightly off resonance; however, this would lower the nominal amplification for which the resonator was designed. Magn Reson Med 54:775-782, 2005.

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Vascular stents as RF antennas for intravascular MR guidance and imaging

Cited by 46 publications

References 36 publications

Artifact-Free Coronary Magnetic Resonance Angiography and Coronary Vessel Wall Imaging in the Presence of a New, Metallic, Coronary Magnetic Resonance Imaging Stent

Artifact-Free Coronary Magnetic Resonance Angiography and Coronary Vessel Wall Imaging in the Presence of a New, Metallic, Coronary Magnetic Resonance Imaging Stent

Microcatheter Tip Enhancement in Fluoroscopy: A Comparison of Techniques

On the heating of inductively coupled resonators (stents) during MRI examinations

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