We present a new algorithm, called marching cubes, that creates triangle models of constant density surfaces from 3D medical data. Using a divide-and-conquer approach to generate inter-slice connectivity, we create a case table that defines triangle topology. The algorithm processes the 3D medical data in scan-line order and calculates triangle vertices using linear interpolation. We find the gradient of the original data, normalize it, and use it as a basis for shading the models. The detail in images produced from the generated surface models is the result of maintaining the inter-slice connectivity, surface data, and gradient information present in the original 3D data. Results from computed tomography (CT), magnetic resonance (MR), and single-photon emission computed tomography (SPECT) illustrate the quality and functionality of marching cubes. We also discuss improvements that decrease processing time and add solid modeling capabilities.

/pdf/marching-cubes-a-high-resolution-3d-surface-construction-3ealswkmtb.pdf

Marching cubes: A high resolution 3D surface construction algorithm

A. Water Exchange 2326 B. Proton Exchange 2327 C. Electronic Relaxation 2327 D. Relaxivity 2331 E. Outerand Second-Sphere Relaxivity 2334 F. Methods of Improving Relaxivity 2336 V. Macromolecular Conjugates 2336 A. Introduction 2336 B. General Conjugation Methods 2336 C. Synthetic Linear Polymers 2336 D. Synthetic Dendrimer-Based Agents 2338 E. Naturally Occurring Polymers (Proteins, Polysaccharides, and Nucleic Acids) 2339

https://mriquestions.com/uploads/3/4/5/7/34572113/lauffer_1999_review.pdf

Gadolinium(III) Chelates as MRI Contrast Agents: Structure, Dynamics, and Applications

The type, frequency, and extent of MR signal abnormalities in Alzheimer9s disease and normal aging are a subject of controversy. With a 1.5-MR unit we studied 12 Alzheimer patients, four subjects suffering from multiinfarct dementia and nine age-matched controls. Punctate or early confluent high-signal abnormalities in the deep white matter, noted in 60% of both Alzheimer patients and controls, were unrelated to the presence of hypertension or other vascular risk factors. A significant number of Alzheimer patients exhibited a more extensive smooth “halo” of periventricular hyperintensity when compared with controls (p = .024). Widespread deep white-matter hyperintensity (two patients) and extensive, irregular periventricular hyperintensity (three patients) were seen in multiinfarct dementia. Areas of high signal intensity affecting hippocampal and sylvian cortex were also present in five Alzheimer and two multiinfarct dementia patients, but absent in controls. Discrete, small foci of deep white-matter hyperintensity are not characteristic of Alzheimer9s disease nor do they appear to imply a vascular cause for the dementing illness. The frequently observed “halo” of periventricular hyperintensity in Alzheimer9s disease may be of diagnostic importance. High-signal abnormalities in specific cortjcal regions are likely to reflect disease processes localized to those structures.

http://www.ajnr.org/content/ajnr/8/3/421.full.pdf

MR Signal Abnormalities at 1.5 T in Alzheimer's Dementia and Normal Aging

Shear wave elasticity imaging (SWEI) is a new approach to imaging and characterizing tissue structures based on the use of shear acoustic waves remotely induced by the radiation force of a focused ultrasonic beam. SWEI provides the physician with a virtual "finger" to probe the elasticity of the internal regions of the body. In SWEI, compared to other approaches in elasticity imaging, the induced strain in the tissue can be highly localized, because the remotely induced shear waves are attenuated fully within a very limited area of tissue in the vicinity of the focal point of a focused ultrasound beam. SWEI may add a new quality to conventional ultrasonic imaging or magnetic resonance imaging. Adding shear elasticity data ("palpation information") by superimposing color-coded elasticity data over ultrasonic or magnetic resonance images may enable better differentiation of tissues and further enhance diagnosis. This article presents a physical and mathematical basis of SWEI with some experimental results of pilot studies proving feasibility of this new ultrasonic technology. A theoretical model of shear oscillations in soft biological tissue remotely induced by the radiation force of focused ultrasound is described. Experimental studies based on optical and magnetic resonance imaging detection of these shear waves are presented. Recorded spatial and temporal profiles of propagating shear waves fully confirm the results of mathematical modeling. Finally, the safety of the SWEI method is discussed, and it is shown that typical ultrasonic exposure of SWEI is significantly below the threshold of damaging effects of focused ultrasound.

Shear wave elasticity imaging: a new ultrasonic technology of medical diagnostics

PURPOSE: To design a segmented inversion-recovery turbo fast low-angle shot (turboFLASH) magnetic resonance (MR) imaging pulse sequence for the visualization of myocardial infarction, compare this technique with other MR imaging approaches in a canine model of ischemic injury, and evaluate its utility in patients with coronary artery disease. MATERIALS AND METHODS: Six dogs and 18 patients were examined. In dogs, infarction was produced and images were acquired by using 10 different pulse sequences. In patients, the segmented turboFLASH technique was used to acquire contrast material–enhanced images 19 days ± 7 (SD) after myocardial infarction. RESULTS: Myocardial regions of increased signal intensity were observed in all animals and patients at imaging. With the postcontrast segmented turboFLASH sequence, the signal intensity of the infarcted myocardium was 1,080% ± 214 higher than that of the normal myocardium in dogs—nearly twice that of the next best sequence tested and approximately 10-fold greater t...

An Improved MR Imaging Technique for the Visualization of Myocardial Infarction

Nuclear magnetic resonance (NMR) imaging was used to study 24-hour-old acute myocardial infarctions in 8 dogs. Images and measurements of excised hearts were obtained in a 6.5 ml bore-resistive NMR imager (0.35 Tesla). Spin echo NMR imaging in each instance demonstrated the area of infarction as a region of increased signal intensity compared with that in normal myocardium. The T1 and T2 values of the area of infarction were greater than those of normal myocardium in all dogs. For each dog the T1 value was greater for the infarct region; however, the group mean value for T1 (ms) of the infarct region (728 ± 94) was not significantly greater than that for the normal region (650 ± 87). The T2 value (ms) was discriminate for all dogs, and the mean value for the infarct region (48 ± 2) was significantly different (p NMR imaging detects acute myocardial infarction as a positive image without contrast media. Increased signal intensity of the infarct is related to increased hydrogen density and increased T2 relaxation time.

Nuclear Magnetic Resonance Imaging of Acute Myocardial Infarction in Dogs: Alterations in Magnetic Relaxation Times

The signal-to-noise ratio (S/N) in magnetic resonance imagining is one of the variables that must be measured when comparing the relative performance of different techniques Although various investigators and official groups have proposed different methods for measuring S/N, these are generally not practical for use by a physician working in a clinical situation The authors present a simple method that should serve for estimating S/N in most cases

Measuring signal-to-noise ratios in MR imaging.

This paper represents a preliminary study of the effects of regional temperature distribution in two-dimensional nuclear magnetic resonance (NMR) T1 imaging. It is found, as expected, that variations in local temperature appear as variations in the corresponding T1 image. The potential use of NMR T1 imaging in temperature measurements is evaluated in the case of water and blood samples. Using containers where the temperature could be either known or directly controlled with reasonable accuracy, images are obtained with samples having at least two regions at different temperatures. As expected, T1 is found to vary linearly with 1/T over the range of 0 degrees C to about 40 degrees C for blood. The potential use of T1 imaging in hyperthermia applications is also discussed.

Temperature distribution measurements in two-dimensional NMR imaging.

The theoretical advantages of nuclear magnetic resonance imaging at higher field strengths are discussed. Examples of images created at 3.5 KGauss (0.35 T) are demonstrated. The authors present a method of collecting several tomographic images sequentially during the time required for a single image.

Nuclear magnetic resonance whole-body imager operating at 3. 5 Kgauss

Although cross-sectional magnetic resonance examination of the head and body is useful for screening large regions of tissue, subsectional regions of the head and body often need to be examined. Orthogonally directed, selectively irradiated planes with different flip angles produce a spatially limited signal region from which two- or three-dimensional volume images can be reconstructed. Images with limited fields-of-view can be acquired in reduced imaging time. We present a general description of this technique. These subsectional or "inner volume" images eliminate respiratory motion artifacts by excluding moving tissues from the imaged volume. A result of this technique is a high signal from rapid pulsatile blood flow, produced without cardiac gating the pulse sequence.

Lawrence E. Crooks

Papers

Nuclear Magnetic Resonance Imaging of Acute Myocardial Infarction in Dogs: Alterations in Magnetic Relaxation Times

Measuring signal-to-noise ratios in MR imaging.

Temperature distribution measurements in two-dimensional NMR imaging.

Nuclear magnetic resonance whole-body imager operating at 3. 5 Kgauss

Inner volume MR imaging: technical concepts and their application.