Positive contrast myeloencephalography for visualization of cerebrospinal fluid fistula

Summary Head injurries are sometimes complicated by cerebrospinal fluid rhinorrhoea. The exact localisation of the fistula is indispensable in cases requiring surgery. This may be achieved by visualization of the fistula with radiopaque substance introduced via the lumbar route and brought into the cranial cavity. This method was successfully used in the case reported here.

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Myeloencephalographie mit positiven Kontrastmitteln für den Nachweis von Liquor-Fisteln

Zusammenfassung Nach lumbaler Injektion von 3 ml Pantopaque wurde das Kontrastmittel unter Röntgenkontrolle in den Schädelinnenraum und zu der Region der vermuteten Liquor-Fistel geleitet. Es gelang ein eindeutiger Nachweis der Frakturstelle.

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Myelo-encephalographie a contraste positif pour la visualisation de fistule liquidienne

Résumé Les traumatismes crâniens se compliquent parfois de rhinorrhée céphalo-rachidienne. Il est indispensable de connaître la localisation exacte de la fistule dans les cas nécessitant une intervention chirurgicale. Ceci peut être réalisé par la mise en évidence de la fistule grâce à un produit radio-opaque introduit par voie lombaire et dirigé dans la cavité crânienne. Cette méthode a été utilisée avec succès dans le cas rapporté.

     

Positive contrast ventriculography in cats with experimental obstructive hydrocephalus.

Cerebrospinal fluid pathways were studied in both normal and experimental obstructed hydrocephalic cats by positive contrast ventriculography. Either water soluble or insoluble contrast material was injected into the lateral cerebral ventricles, and radiographs were taken of the head and spinal cord. In the normal cat, the contrast material freely flowed throughout the spinal fluid spaces. The contrast material accumulated in the cisterna magna, and from there extended into the cranial and spinal subarachnoid spaces. In the kaolin-induced hydrocephalic cat, the outlets from the fourth ventricle were obstructed, and direct communication between the ventricular system and the subarachnoid spaces no longer existed. In these cats, the contrast material passed directly down the central canal of spinal cord and its movement was followed throughout the entire length of the canal. At the lower lumbar-sacral regions, the material perforated the cord and flowed into the subarachnoid space. At all levels, the central canal was enlarged and local dilatations were seen extending dorsally.     

Positive contrast visualization of nitinol devices using susceptibility gradient mapping

MRI visualization of devices is traditionally based on signal loss due to T₂* effects originating from local susceptibility differences. To visualize nitinol devices with positive contrast, a recently introduced postprocessing method is adapted to map the induced susceptibility gradients. This method operates on regular gradient‐echo MR images and maps the shift in k‐space in a (small) neighborhood of every voxel by Fourier analysis followed by a center‐of‐mass calculation. The quantitative map of the local shifts generates the positive contrast image of the devices, while areas without susceptibility gradients render a background with noise only. The positive signal response of this method depends only on the choice of the voxel neighborhood size. The properties of the method are explained and the visualizations of a nitinol wire and two stents are shown for illustration. Magn Reson Med 60:588–594, 2008. © 2008 Wiley‐Liss, Inc.     

Positive contrast visualization of SPIO-labeled pancreatic islets using echo-dephased steady-state free precession

Objective  

MRI has recently been introduced as a promising method of monitoring the transplanted pancreatic islets labelled with superparamagnetic iron oxide (SPIO). However, the traditional T₂^* {\hbox{T}}_2^* -weighted approach frequently yields ambiguous results because of the negative contrast of the SPIO particles on the background of other body components. This obstacle could be overcome with the use of a novel method known as echo-dephased steady state free precession (SSFP), generating positive contrast in the presence of paramagnetic material.     

Positive contrast magnetic resonance imaging of cells labeled with magnetic nanoparticles.

Contrast agents incorporating superparamagnetic iron-oxide nanoparticles have shown promise as a means to visualize labeled cells using MRI. Labeled cells cause significant signal dephasing due to the magnetic field inhomogeneity induced in water molecules near the cell. With the resulting signal void as the means for detection, the particles behave as a negative contrast agent, which can suffer from partial-volume effects. In this paper, a new method is described for imaging labeled cells with positive contrast. Spectrally selective RF pulses are used to excite and refocus the off-resonance water surrounding the labeled cells so that only the fluid and tissue immediately adjacent to the labeled cells are visible in the image. Phantom, in vitro, and in vivo experiments show the feasibility of the new method. A significant linear correlation (r = 0.87, P < 0.005) between the estimated number of cells and the signal was observed.     

超顺磁性氧化铁标记的胰岛在回波去相位稳态自由进动序列中的阳性强化成像

目的近期研究认为MRI是一种可以用于监测超顺磁性氧化铁(SPIO)标记移植胰岛的有效检查方法。然而由于背景中SPIO微粒在体部其他部分形成的阴性对比,常规     

Positive and negative contrast agents in CT evaluation of the abdomen and pelvis

The oral administration of a dilute positive iodinated contrast agent such as 2% Gastrografin is usually necessary to achieve optimal delineation of abdominal and pelvic organs. The amount of contrast agent administered and the timing of its administration depends on the site of suspected disease within the body. The simultaneous administration of antiperistaltic agents intravenously is generally unnecessary when utilizing the modern fast CT scanners. However, contrast agent-induced artifact may at times be troublesome, and we therefore suggest that lesions in the left lobe of the liver be scanned without positive contrast in the stomach. Negative contrast may also be useful in delineating disease: gas (carbon dioxide) has been shown to be useful in evaluating bladder tumors. We have also used air insufflation to facilitate the evaluation of small rectal tumors. Intravenous administration of contrast agent aids characterization of various disease entities and also facilitates the recognition of vascular structures (such as veins and arteries in the peripancreatic region). In our opinion both the infusion and bolus modes of contrast material administration have their place in the evaluation of abdominal and pelvic lesions by computed tomography. Newer techniques such as dynamic CT scanning will probably prove to be valuable both in delineating and characterizing disease.     

Positive contrast imaging of iron oxide nanoparticles with susceptibility‐weighted imaging

Superparamagnetic iron oxide particles can be utilized to label cells for immune cell and stem cell therapy. The labeled cells cause significant field distortions induced in their vicinity, which can be detected with magnetic resonance imaging (MRI). In conventional imaging, the signal voids arising from the field distortions lead to negative contrast, which is not desirable, as detection of the cells can be masked by native low signal tissue. In this work, a new method for visualizing magnetically labeled cells with positive contrast is proposed and described. The technique presented is based on the susceptibility‐weighted imaging (SWI) post‐processing algorithm. Phase images from gradient‐echo sequences are evaluated pixel by pixel, and a mask is created with values ranging from 0 to 1, depending on the phase value of the pixel. The magnitude image is then multiplied by the mask. With an appropriate mask function, positive contrast in the vicinity of the labeled cells is created. The feasibility of this technique is proved using an agar phantom containing superparamagnetic iron oxide particles–labeled cells and an ex vivo bovine liver. The results show high potential for detecting even small labeled cell concentrations in structurally inhomogeneous tissue types. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.     

Positive contrast MR-lymphography using inversion recovery with ON-resonant water suppression (IRON)

PURPOSE: To investigate the utility of inversion recovery with ON-resonant water suppression (IRON) to create positive signal in normal lymph nodes after injection of superparamagnetic nanoparticles. MATERIALS AND METHODS: Experiments were conducted on six rabbits, which received a single bolus injection of 80 mumol Fe/kg monocrystalline iron oxide nanoparticle (MION-47). Magnetic resonance imaging (MRI) was performed at baseline, 1 day, and 3 days after MION-47 injection using conventional T(1)- and T(2)*-weighted sequences and IRON. Contrast-to-noise ratios (CNR) were measured in blood and in paraaortic lymph nodes. RESULTS: On T(2)*-weighted images, as expected, signal attenuation was observed in areas of paraaortic lymph nodes after MION-47 injection. However, using IRON the paraaortic lymph nodes exhibited very high contrast enhancement, which remained 3 days after injection. CNR with IRON was 2.2 +/- 0.8 at baseline, increased markedly 1 day after injection (23.5 +/- 5.4, P < 0.01 vs. baseline), and remained high after 3 days (21.8 +/- 5.7, *P < 0.01 vs. baseline). CNR was also high in blood 1 day after injection (42.7 +/- 7.2 vs. 1.8 +/- 0.7 at baseline, P < 0.01) but approached baseline after 3 days (1.9 +/- 1.4, P = NS vs. baseline). CONCLUSION: IRON in conjunction with superparamagnetic nanoparticles can be used to perform 'positive contrast' MR-lymphography, particularly 3 days after injection of the contrast agent, when signal is no longer visible within blood vessels. The proposed method may have potential as an adjunct for nodal staging in cancer screening.