Principles of nuclear magnetic resonance imaging.

Pykett, I L; Newhouse, J H; Buonanno, Ferdinando S.; Brady, Thomas J.; Goldman, M.; Kistler, J P; Pohost, Gerald M.

doi:10.1148/radiology.143.1.7038763

Cited by 255 publications

(43 citation statements)

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“…[3][4][5] Although these studies have clearly demonstrated that relaxation times change in the presence of ischemia, the relationship between these changes and the degree of ischemia has not been defined. The purposes of the present study were (1) to examine the effects of a 3 hr occlusion time on myocardial T1 and T2 relaxation times, (2) to measure the additional effect of reperfusion on these relaxation parameters, (3) to determine the relationship between relaxation times and regional myocardial blood flow, and (4) to qualitatively assess the relationship between spectroscopically measured relaxation times and T1-and T2-weighted magnetic resonance images.…”

mentioning

confidence: 99%

Assessment of myocardial ischemia with proton magnetic resonance: effects of a three hour coronary occlusion with and without reperfusion.

Johnston¹,

Brady²,

Ratner³

et al. 1985

Circulation

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Proton (hydrogen-1) magnetic resonance imaging techniques have potential for the detection and characterization of changes associated with myocardial ischemia. Since image contrast is dependent on TI and T2 relaxation times, we examined these parameters in a canine preparation of occlusion of the left anterior descending coronary artery. Of 16 dogs studied, seven underwent 3 hr of coronary artery occlusion and nine underwent 3 hr of occlusion followed by 1 hr of reperfusion. After the dogs were killed, the hearts of four from each group were imaged in a small bore, 1.4 tesla magnet. From all hearts myocardial segments were obtained from the normal zone and the central ischemic zone (CZ). These segments were divided into epicardial and endocardial sections and studied in a spectrometer (20 MHz). After 3 hr of occlusion, CZ endocardial Ti and T2 increased significantly (p < .01 and p < .05, respectively). Changes in CZ epicardial relaxation times were not as marked. Although Tl and T2 tended to be higher in the reperfused group compared with the nonreperfused group, the differences did not reach statistical significance. In keeping with the spectrometric findings, Ti-dependent inversion recovery images and T2-dependent spin-echo images of the excised hearts demonstrated excellent contrast between normal and ischemic myocardium. Modest correlations were noted for both groups between blood flows during occlusion measured by the microsphere technique and TI and T2 relaxation times. In summary, relaxation times Tl and T2 increase regionally after 3 hr of coronary artery occlusion and tend to be accentuated by reperfusion. These changes are associated with high-resolution magnetic resonance image contrast, suggesting that such imaging may be useful for the characterization of early myocardial ischemia.Circulation 71, No. 3, 595-601, 1985. MAGNETIC resonance imaging provides a potentially useful method for noninvasive detection and characterization of early myocardial ischemia. Since signal intensity is dependent in part on T1 and T2 relaxation times,' delineation of these parameters after an ischemic insult is of importance in predicting image con-

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mentioning

confidence: 99%

Assessment of myocardial ischemia with proton magnetic resonance: effects of a three hour coronary occlusion with and without reperfusion.

Johnston¹,

Brady²,

Ratner³

et al. 1985

Circulation

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“…In Magnetic Resonance Imaging (MRI) system, gradient coils are used to generate linear gradient magnetic fields that are superimposed on a strong uniform magnetic field [1]. The performance of the gradient coils can significantly affect the imaging quality and enable new sequences and, consequently, gradient coil designs continue to evolve.…”

Section: Introductionmentioning

confidence: 99%

Design of transverse head gradient coils using a layer-sharing scheme

Wang

Zhou

et al. 2017

Journal of Magnetic Resonance

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In this paper, a new design for transverse asymmetric head gradient coils is proposed for magnetic resonance imaging (MRI). Unlike the conventional coil designs where the x and y coils are placed onto separate radial layers, the new design has windings for both the x and y coils in each transverse coil layer. The coil performance using the new design was compared with the conventional coils with the same dimensions and constraints. The results showed that the new design can improve coil performance in terms of a lower inductance, lower resistance and a higher figure of merit.

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“…(3-1) and Eqs. (3-3)- (3)(4)(5) were calculated by the sum of the finite difference grids. The current density at the centre of the grid was used to represent the discrete value of the whole grid.…”

Section: Finite Difference Methods For Gradient Coil Designmentioning

confidence: 99%

“…The expression of such a quasi-elliptic curve is given in Eq. (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13), where Y 0 and Z 0 are the semi-major axis and semi-minor axis lengths, respectively, with the power p being usually equal to or larger than 1. To make a spiral connection between the coil loops, a quasi-conical base was imagined, and the coil curve was first wound around the surface of the base, and then a mathematical transform was applied to map the curve to the coil cylinder.…”

Section: Discrete Wire Methods For Gradient Coil Designmentioning

confidence: 99%

“…The superimposed gradient magnetic field slightly changes the proton precession frequency or phase, thus encoding the spatial information of an imaged object in the frequency associated with a position in space [4]. In general, the magnetic field gradient produced by the gradient coils is required to be as linear as possible, and a well-designed gradient coil should also have low inductance, low resistance, high efficiency, etc.…”

Section: From Gradient Coil Design To Acoustic Noise Controlmentioning

confidence: 99%

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Gradient coil design and acoustic noise control in magnetic resonance imaging systems

Wang¹

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In magnetic resonance imaging (MRI), three-dimensional linearly varied magnetic field gradients are required in the imaging volume, for the encoding of the spatial information of the imaged object.The gradient magnetic field is generated by gradient coils, whose performance directly affects the final MR image quality. Modern MRI applications demand gradient coils to be designed with higher performance such as a faster slew rate for rapid imaging, and fewer system interactions to ensure distortion-free images.During MR imaging, the gradient coil current switches quickly and the alternating current under a strong magnetic field generates a large Lorentz force, thus increasing the vibrations and noise in the gradient assembly, and the vibrations can also transmit to other components in the system. Moreover, the gradient magnetic field induces eddy currents on the surrounding conductive materials, resulting in further mechanical vibration. The sound pressure level (SPL) of an MRI scanner very commonly exceeds 100 dB, which may be discomforting to patients. Therefore, an effective acoustic noise control is necessary for the MRI operation.This thesis attempts to design a novel gradient coil system in an MRI scanner with a particular focus on the investigation of an acoustic noise control scheme. A brief summary of the thesis work is as follows.(1) Gradient coil design A conventional cylindrical MRI scanner has a long patient bore, which may make some patients uneasy due to claustrophobia. In order to alleviate this, an asymmetric gradient coil was proposed to accommodate an asymmetric MRI magnet. The coil was designed with a number of features, for example, to enable the installation of the shim tray, the coil was configured with one end connected and the other end separated. The electromagnetic and acoustic performances were also improved compared with a conventional non-connected coil system.The stream function approach is commonly used in gradient coil design, but an issue with this design is a connection problem between coil loops. To eliminate the field errors due to the coil connections, this thesis proposed a novel spiral coil design scheme, including both transverse coils and a longitudinal coil. The proposed coil design method was not only able to improve the magnetic II performance of the coil, but also could integrate the cooling system into the coil design using hollow wires in the discrete wire space.Wire spacing is a major engineering problem in gradient coil design. Conventional gradient coils are designed with three primary layers and three shielding layers, and in general, primary transverse coils are located in two layers separated by a very dense wire structure. In this thesis, a novel gradient coil design strategy using a layer-sharing scheme was proposed. This design scheme mutually combined the x and y gradient coil layers, effectively utilizing the unoccupied or sparse coil-layer space. The new method was modelled in the case of an asymmetric head coil design, and enhanced coil performan...

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Principles of nuclear magnetic resonance imaging.

Cited by 255 publications

References 0 publications

Assessment of myocardial ischemia with proton magnetic resonance: effects of a three hour coronary occlusion with and without reperfusion.

Assessment of myocardial ischemia with proton magnetic resonance: effects of a three hour coronary occlusion with and without reperfusion.

Design of transverse head gradient coils using a layer-sharing scheme

Gradient coil design and acoustic noise control in magnetic resonance imaging systems

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