Magnetic resonance imaging apparatus

Optical spectroscopy, imaging, and therapy tissue phantoms must have the scattering and absorption properties that are characteristic of human tissues, and over the past few decades, many useful models have been created. In this work, an overview of their composition and properties is outlined, by separating matrix, scattering, and absorbing materials, and discussing the benefits and weaknesses in each category. Matrix materials typically are water, gelatin, agar, polyester or epoxy and polyurethane resin, room-temperature vulcanizing (RTV) silicone, or polyvinyl alcohol gels. The water and hydrogel materials provide a soft medium that is biologically and biochemically compatible with addition of organic molecules, and are optimal for scientific laboratory studies. Polyester, polyurethane, and silicone phantoms are essentially permanent matrix compositions that are suitable for routine calibration and testing of established systems. The most common three choices for scatters have been: (1.) lipid based emulsions, (2.) titanium or aluminum oxide powders, and (3.) polymer microspheres. The choice of absorbers varies widely from hemoglobin and cells for biological simulation, to molecular dyes and ink as less biological but more stable absorbers. This review is an attempt to indicate which sets of phantoms are optimal for specific applications, and provide links to studies that characterize main phantom material properties and recipes.

https://www.spiedigitallibrary.org/journals/journal-of-biomedical-optics/volume-11/issue-4/041102/Review-of-tissue-simulating-phantoms-for-optical-spectroscopy-imaging-and/10.1117/1.2335429.pdf

Review of tissue simulating phantoms for optical spectroscopy, imaging and dosimetry

A shielded medical device implanted in a biological organism. The device has a magnetic shield, and the magnetic shield contains a layer of nanomagnetic material; such layer has a morphological density of at least 98 percent; and it is bonded to the medical device by means of an interlayer with a thickness of less than about 10 microns. The nanomagnetic material in such layer has a saturation magnetization of from about 1 to about 36,000 Gauss, a coercive force of from about 0.01 to about 5,000 Oersteds, a relative magnetic permeability of from about 1 to about 500,000, and an average particle size of less than about 100 nanometers.

Magnetically shielded assembly

The characterization and calibration of ultrasound imaging systems requires tissue-mimicking phantoms with known acoustic properties, dimensions and internal features. Tissue phantoms are available commercially for a range of medical applications. However, commercial phantoms may not be suitable in ultrasound system design or for evaluation of novel imaging techniques. It is often desirable to have the ability to tailor acoustic properties and phantom configurations for specific applications. A multitude of tissue-mimicking materials and phantoms are described in the literature that have been created using a variety of materials and preparation techniques and that have modeled a range of biological systems. This paper reviews ultrasound tissue-mimicking materials and phantom fabrication techniques that have been developed over the past four decades, and describes the benefits and disadvantages of the processes. Both soft tissue and hard tissue substitutes are explored.

A review of tissue substitutes for ultrasound imaging.

McDonaldʼs Blood Flow in Arteries

A new, fast, 2D MR imaging technique allowing passive catheter visualization adequate for use as a tool for guiding the movement of a catheter during endovascular procedures is described. This imaging technique samples low spatial frequencies more often than high spatial frequencies; it also uses both k-space view sharing and temporal interpolation. Unlike other techniques for passive visualization that exploit magnetic-susceptibility-induced artifacts, we have adopted a strategy that takes advantage of the T1-shortening effect of paramagnetic contrast agents, such as Gd-DTPA and a projection dephaser. This not only permits visualization of the entire catheter length but also minimizes the risk of intravascular heating. Using this method, a temporal frame rate of up to eight images per second and a tip localization accuracy of +/- 1mm (root mean square difference) can be achieved.

A rapid 2D time-resolved variable-rate k-space sampling MR technique for passive catheter tracking during endovascular procedures

Real-Time MR Imaging-guided Passive Catheter Tracking with Use of Gadolinium-filled Catheters

Materials that simultaneously mimic soft tissue in vivo for magnetic resonance imaging (MRI), ultrasound (US), and computed tomography (CT) for use in a prostate phantom have been developed. Prostate and muscle mimicking materials contain water, agarose, lipid particles, protein, Cu++, EDTA, glass beads, and thimerosal (preservative). Fat was mimicked with safflower oil suffusing a random mesh (network) of polyurethane. Phantom material properties were measured at 22 degrees C. (22 degrees C is a typical room temperature at which phantoms are used.) The values of material properties should match, as well as possible, the values for tissues at body temperature, 37 degrees C. For MRI, the primary properties of interest are T1 and T2 relaxations times, for US they are the attenuation coefficient, propagation speed, and backscatter, and for CT, the x-ray attenuation. Considering the large number of parameters to be mimicked, rather good agreement was found with actual tissue values obtained from the literature. Using published values for prostate parenchyma, T1 and T2 at 37 degrees C and 40 MHz are estimated to be about 1,100 and 98 ms, respectively. The CT number for in vivo prostate is estimated to be 45 HU (Hounsfield units). The prostate mimicking material has a T1 of 937 ms and a T2 of 88 ms at 22 degrees C and 40 MHz; the propagation speed and attenuation coefficient slope are 1,540 m/s and 0.36 dB/cm/MHz, respectively, and the CT number of tissue mimicking prostate is 43 HU. Tissue mimicking (TM) muscle differs from TM prostate in the amount of dry weight agarose, Cu++, EDTA, and the quality and quantity of glass beads. The 18 microm glass beads used in TM muscle increase US backscatter and US attenuation; the presence of the beads also has some effect on T1 but no effect on T2. The composition of tissue-mimicking materials developed is such that different versions can be placed in direct contact with one another in a phantom with no long term change in US, MRI, or CT properties. Thus, anthropomorphic phantoms can be constructed.

/pdf/tissue-mimicking-materials-for-a-multi-imaging-modality-187frdnfd1.pdf

Tissue mimicking materials for a multi-imaging modality prostate phantom.

The present invention provides a coating that emits magnetic resonance signals and a method for coating medical devices therewith. The coating includes a paramagnetic metal ion-containing polymer complex that facilitates diagnostic and therapeutic techniques by readily visualizing medical devices coated with the complex.

Orhan Unal

Papers

A rapid 2D time-resolved variable-rate k-space sampling MR technique for passive catheter tracking during endovascular procedures

Real-Time MR Imaging-guided Passive Catheter Tracking with Use of Gadolinium-filled Catheters

Tissue mimicking materials for a multi-imaging modality prostate phantom.

MR signal-emitting coatings

MR-guided angioplasty of renal artery stenosis in a pig model: a feasibility study.