Utilizing different methods for visualizing susceptibility from a single multi-gradient echo dataset

Varma, Gopal; Pedersen, Steen; Taupitz, Matthias; Botnar, René M.; Dahnke, Hannes; Keevil, Stephen; Schaeffter, Tobias

doi:10.1007/s10334-009-0180-4

Cited by 11 publications

(11 citation statements)

References 23 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…As in other positive contrast techniques, SUMO cannot differentiate positive contrast generated by the devices from other unrelated sources of susceptibility (e.g., air‐to‐tissue interfaces). This ambiguity may be reduced by taking the direction, size, and shape of the susceptibility gradient generated from the devices into account (7).…”

Section: Discussionmentioning

confidence: 99%

“…Therefore, a more reliable MR-visualization of metallic devices is of interest.In MRI, the visualization of metallic devices such as endovascular stent grafts or prostate brachytherapy seeds (6) is traditionally based on signal voids due to local susceptibility gradients. It has been shown that for better visualization of devices, it is attractive to convert the signal loss into positive contrast (7). For this, a variety of positive contrast techniques have been proposed (8,9), but often require optimization based on the magnitude of the local field gradients and local off-resonance effects.…”

mentioning

confidence: 99%

See 1 more Smart Citation

Positive visualization of implanted devices with susceptibility gradient mapping using the original resolution

et al. 2010

Self Cite

View full text Add to dashboard Cite

In magnetic resonance imaging, implantable devices are usually visualized with a negative contrast. Recently, positive contrast techniques have been proposed, such as susceptibility gradient mapping (SGM). However, SGM reduces the spatial resolution making positive visualization of small structures difficult. Here, a development of SGM using the original resolution (SUMO) is presented. For this, a filter is applied in k-space and the signal amplitude is analyzed in the image domain to determine quantitatively the susceptibility gradient for each pixel. It is shown in simulations and experiments that SUMO results in a better visualization of small structures in comparison to SGM. SUMO is applied to patient datasets for visualization of stent and prostate brachytherapy seeds. In addition, SUMO also provides quantitative information about the number of prostate brachytherapy seeds. The method might be extended to application for visualization of other interventional devices, and, like SGM, it might also be used to visualize magnetically labelled cells. Computed tomography (CT) is currently the imaging modality of choice to assess the position of implantable devices such as endovascular stent grafts (1) or prostate brachytherapy seeds (2). Although CT allows relatively easy visualization of stents, their functional assessment (patency) by flow measurements is limited. Furthermore, CT is used to assess the dosimetry of prostate brachytherapy seeds post implant. However, due to the limited soft tissue contrast of CT, the prostate is often not adequately depicted, which can result in overestimation of its volume (3). Magnetic resonance imaging (MRI), which provides superior soft-tissue imaging and no known biologically harmful effects, is becoming an alternative modality to guide and assess interventional procedures. Combined X-ray radiography and MRI systems have been shown to provide an alternative method for combining the advantages of MRI with a more accurate device depiction from X-ray (4,5). However, coregistration of MR and X-ray data is subject to error from movement and/or misregistration. Therefore, a more reliable MR-visualization of metallic devices is of interest.In MRI, the visualization of metallic devices such as endovascular stent grafts or prostate brachytherapy seeds (6) is traditionally based on signal voids due to local susceptibility gradients. It has been shown that for better visualization of devices, it is attractive to convert the signal loss into positive contrast (7). For this, a variety of positive contrast techniques have been proposed (8,9), but often require optimization based on the magnitude of the local field gradients and local off-resonance effects. These are either applied during image acquisition or in a postprocessing step afterward. In particular, susceptibility gradient mapping (SGM) allows the production of a positive contrast image from the acquired complex image data (10). For this, a short-term Fourier transform (STFT) is applied for each pixel computed over a small number ...

show abstract

Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

Positive visualization of implanted devices with susceptibility gradient mapping using the original resolution

et al. 2010

Self Cite

View full text Add to dashboard Cite

show abstract

“…Even with the relatively low iron concentration of 29 mmol Fe kg À1 body weight, the in vivo CNR for SGM was still greater than 5, which is assumed to be the lower detection limit for molecular imaging (30). Recently, Varma et al (31) introduced a white marker post-processing approach with a three-dimensional (3D) acquisition, which might resolve these issues. White marker did not show positive contrast in tumor areas where contrast was observed with R 2 * mapping, GE or SGM (Fig.…”

Section: Comparison Of Different Mri Techniquesmentioning

confidence: 99%

“…Probably this contribution is too small to be detected in vivo. Recently, Varma et al (31) introduced a white marker post-processing approach with a three-dimensional (3D) acquisition, which might resolve these issues.…”

Section: Comparison Of Different Mri Techniquesmentioning

confidence: 99%

Efficacy of positive contrast imaging techniques for molecular MRI of tumor angiogenesis

Wolters

Oostendorp

Coolen

et al. 2012

Contrast Media & Molecular

View full text Add to dashboard Cite

Superparamagnetic iron oxide particles (SPIOs) are promising contrast agents for molecular MRI. To improve the in vivo detection of iron-based contrast media, positive contrast imaging techniques have been developed. Here, the efficacy of two positive contrast techniques, white marker and susceptibility gradient mapping (SGM), were evaluated for molecular MRI of tumor angiogenesis and compared with conventional negative contrast gradient echo (GE) imaging. In vitro, cylindrical phantoms containing varying iron oxide concentrations were used to measure the response of positive contrast techniques. In vivo, tumor bearing mice were used as a model for tumor angiogenesis. Mice were injected with unlabeled SPIOs (n = 5) or SPIOs labeled with cyclic NGR peptide (cNGR) (n = 5), which homes specifically to angiogenic microvessels. Pre- and post-contrast GE and white marker images were acquired. Subsequently, SGM images and R(2)(*) maps were calculated. For image analysis, the contrast-to-noise ratio (CNR) and the percentage of enhanced voxels (EVs) in the tumor rim and core were calculated. In vitro, the linear increases in MRI signal response for increasing iron oxide concentration were much stronger for SGM than white marker. In vivo, the CNR of GE, white marker and SGM imaging was 5.7, 1.2 and 6.2, respectively, with equal acquisition times. Significant differences in the percentage of EVs between the tumor rim and core were found using R(2)(*) mapping, GE and SGM (p < 0.05). The two contrast agents had significantly different percentages of EVs by R(2)(*) mapping and SGM in the rim (p < 0.001). The in vivo efficacy of white marker and SGM was evaluated for molecular MRI relative to GE imaging and R(2)(*) mapping. Only SGM, and not white marker, can be used to transfer the negative contrast from targeted SPIOs in a positive contrast signal without loss of CNR.

show abstract

“…MR imaging of cells in vivo is commonly performed using gradient-or spin-echo sequences for T 2 -or T 2 *weighted negative-contrast imaging of cells labeled with ultra-small superparamagnetic iron-oxide (USPIO) nanoparticles (8)(9)(10). Negative-contrast methods image the accumulation of USPIO nanoparticles through loss of signal due to the strong T 2 * dephasing induced locally by the presence of the superparamagnetic nanoparticles.…”

mentioning

confidence: 99%

Combined off‐resonance imaging and T2 relaxation in the rotating frame for positive contrast MR imaging of infection in a murine burn model

Andronesi

Mintzopoulos

Psychogios

et al. 2010

Magnetic Resonance Imaging

View full text Add to dashboard Cite

Purpose: To develop novel magnetic resonance (MR) imaging methods to monitor accumulation of macrophages in inflammation and infection. Positive-contrast MR imaging provides an alternative to negative-contrast MRI, exploiting the chemical shift induced by ultra-small superparamagnetic iron-oxide (USPIO) nanoparticles to nearby water molecules. We introduce a novel combination of off-resonance (ORI) positive-contrast MRI and T 2r relaxation in the rotating frame (ORI-T 2r ) for positive-contrast MR imaging of USPIO.Materials and Methods: We tested ORI-T 2r in phantoms and imaged in vivo the accumulation of USPIO-labeled macrophages at the infection site in a mouse model of burn trauma and infection with Pseudomonas aeruginosa (PA). PA infection is clinically important. The USPIO nanoparticles were injected directly in the animals in solution, and macrophage labeling occurred in vivo in the animal model. Results:We observed a significant difference between ORI-T 2r and ORI, which leads us to suggest that ORI-T 2r is more sensitive in detecting USPIO signal. To this end, the ORI-T 2r positive contrast method may prove to be of higher utility in future research. Conclusion:Our results may have direct implications in the longitudinal monitoring of infection, and open perspectives for testing novel anti-infective compounds.

show abstract

Utilizing different methods for visualizing susceptibility from a single multi-gradient echo dataset

Abstract: Combined T*2-weighted imaging and SGM using the same complex image data was found to provide complementary information and high sensitivity to detect distortion inducing agents.

Cited by 11 publications

References 23 publications

Positive visualization of implanted devices with susceptibility gradient mapping using the original resolution

Positive visualization of implanted devices with susceptibility gradient mapping using the original resolution

Efficacy of positive contrast imaging techniques for molecular MRI of tumor angiogenesis

Combined off‐resonance imaging and T2 relaxation in the rotating frame for positive contrast MR imaging of infection in a murine burn model

Contact Info

Product

Resources

About