Atlas-based automated positioning of outer volume suppression slices in short-echo time 3D MR spectroscopic imaging of the human brain.

Spatial suppression of peripheral lipid-containing regions in volumetric MR spectroscopic imaging of the human brain requires placing large numbers of outer volume suppression (OVS) slices, which is time-consuming, prone to operator error and may introduce subject-dependent variability in volume coverage. We developed a novel, computationally efficient atlas-based approach for automated positioning of up to 16 OVS slices and the MR spectroscopic imaging slab. Standardized positions in Montreal Neurological Institute atlas space were established offline using a recently developed iterative optimization procedure. During the scanning session, positions in subject space were computed using affine transformation of standardized positions in Montreal Neurological Institute space. Offline analysis using magnetization prepared rapid gradient echo scans from 11 subjects demonstrated reliable OVS placement, comparable with but faster than iterative placement in subject space. This atlas-based method was further validated in 14 subjects using 3D short-echo time proton-echo-planar-spectroscopic-imaging at 3 T. Comparison of manual and automatic placement using 8 OVS slices demonstrated consistent MR spectroscopic imaging volume selection and comparable spectral quality with similar degree of lipid suppression and number of usable voxels. Automated positioning of 16 OVS slices enabled larger volume coverage, while maintaining similar spectral quality and lipid suppression. Atlas-based automatic prescription of short echo time MR spectroscopic imaging is expected to be advantageous for longitudinal and cross-sectional studies.

Automatic placement of outer volume suppression slices in MR spectroscopic imaging of the human brain.

Spatial suppression of peripheral regions (outer volume suppression) is used in MR spectroscopic imaging to reduce contamination from strong lipid and water signals. The manual placement of outer volume suppression slices requires significant operator interaction, which is time consuming and introduces variability in volume coverage. Placing a large number of outer volume saturation bands for volumetric MR spectroscopic imaging studies is particularly challenging and time consuming and becomes unmanageable as the number of suppression bands increases. In this study, a method is presented that automatically segments a high-resolution MR image in order to identify the peripheral lipid-containing regions. This method computes an optimized placement of suppression bands in three dimensions and is based on the maximization of a criterion function. This criterion function maximizes coverage of peripheral lipid-containing areas and minimizes suppression of cortical brain regions and regions outside of the head. Computer simulation demonstrates automatic placement of 16 suppression slices to form a convex hull that covers peripheral lipid-containing regions above the base of the brain. In vivo metabolite mapping obtained with short echo time proton-echo-planar spectroscopic imaging shows that the automatic method yields a placement of suppression slices that is very similar to that of a skilled human operator in terms of lipid suppression and usable brain voxels.

A birdcage model for the Chinese meridian system: Part V: Applications to animals and plants.

Since we all belong to the Kingdom Animalia, it is not surprising that animals in general benefit from the healing art of acupuncture that helps humans. Consequently, any proposed mechanism of Qi and acupuncture for humans based on animal physiology is probably applicable to animals as well, yet none is capable of explaining most of the complicated physiological effects observed. Not much attention was paid to the effects of Qi and acupuncture on plants (Kingdom Plantae) and on enoki mushrooms (Kingdom Fungi) by the TCM community, probably because they cannot be explained in terms of neurochemistry or connective tissue structures. However, our transmission and birdcage model is in principle applicable across Kingdom boundaries, because it is based on physical properties underlying the biological structure, thus its explanatory power is not restricted by categories of biology. We estimate several possible parameters of the birdcage model for animals and plants and give a possible interpretation for the sound fertilization phenomenon.

Birdcage model for the Chinese meridian system: part VI. meridians as the primary regulatory system.

It is imperative to define the fundamental concepts of Qi, channels, and the meridian system of Chinese medicine in terms of scientific terminology before any meaningful and mutually beneficial dialog can begin between Chinese and Western medicine. In the Chinese theory, the meridian system as a whole is the system of the body. We propose the existence of a meridian regulatory system that governs interactions between and adjusts functions of internal organs, connects them to the body surface through a network of pathways (channels) and displays their status on the skin. The meridian systems is analyzed as a 28-leg, uniform, low pass birdcage coil, where each leg represents a channel. The channel is analyzed as a transmission line and Qi is the standing wave riding on it. Each segment in the channel is represented as a section of the transmission line and it is in natural oscillation, with its second lowest resonant frequency being the 50-round circulation frequency f50, 0.578 x 10(-3) Hz.

A birdcage model for the Chinese meridian system: part III. Possible mechanism of magnetic therapy.

Based on the electromagnetic model of the transmission line for the channel and the birdcage resonator for the meridian network, we interpret two effects, seemingly incomprehensible in terms of current Western physiology, the lasting effect and the remote effect. For the lasting effect, acupuncture enhances the amplitude of the Qi standing wave, and this increased amplitude is retained and thus is able to sustain a gradual remodeling of the extracellular matrix in interstitial connective tissues, resulting in a lasting therapeutic effect. For the remote effect (acupuncture effect far from the site of needle insertion), our model puts the mechanism of magnetic therapy on an equal footing with that of acupuncture. It may not be a coincidence that accounts of investigators in both acupuncture and magnetotherapy about the depth of the effective site--along cleavage planes between muscles, or between muscle and bone or tendon--are in accord with that of the Huang Di Nei Jing about the course of channels: "they are embedded and travel between interstitial muscles, deep and invisible." A possible magnetic field generated outside the birdcage may be manipulated to produce local areas of higher temperature or very strong fields.

A birdcage model for the Chinese meridian system: part II. The meridian system as a birdcage resonator.

We propose that the meridian system as a whole is one grand transmission line, excited periodically at a frequency of f50, the frequency of the 50-round circulation (0.578 x 10(-3) Hz). This grand transmission line is analyzed as a 28-leg, uniform, low pass (LP) electromagnetic (EM) birdcage coil, consisting of capacitors and inductors. The second lowest resonant frequency (mode 1) of the birdcage is f50. Each leg represents one channel and is analyzed as a lossless transmission line itself. The amplitude of the Qi standing wave on each channel is periodically amplified at f50. The average number of acupoints on the 28 channels involved in the 50-round circulation and the speed of Qi were used to calculate the resonant frequencies. A mechanical birdcage consisting of mass and spring may co-exist and exchange energy with the EM birdcage. Magnetic resonance imaging (MRI) may be used to map the diffusion coefficient, elastic modulus and electric conductivity of tissues in vivo, as an indirect evidence of the existence of the proposed EM and mechanical standing waves.

A birdcage model for the Chinese Meridian System: part I. A channel as a transmission line.

The concept of Qi and the concept of channel are so closely related that they must be defined and comprehended simultaneously in a coordinated fashion. Once the nature of Qi is established in terms of physics, we may be able to explain the functional role that the channels play, as well as explain other Chinese medical terminology with a language of modem science. Based on the low electrical impedance characteristics of acupoints, we propose that the meridian channel is equivalent to an electromagnetic transmission line and the Qi is the electromagnetic (EM) standing wave riding on the line, with acupoints as its nodes. The standing wave within each segment of the channel separated by acupoints is in natural oscillation thus the segment may be analyzed as a lambda/4 open circuit that behaves like a series RLC resonator. Acupuncture until De Qi is effectively equivalent to charging the capacitor Ceq of the RLC resonator in the transmission line. The mechanism of bu and xie are charging or discharging the capacitor to bring the capacititive (or inductive) behavior of the segment back to that of the resonant state. Kirlian photograph may serve as a visual observation of the EM waves on channels.

Empirical models of transverse relaxation for spherical magnetic perturbers.

Ferromagnetic or superparamagnetic particles as MRI contrast agent present many advantages for bringing about soft tissue contrast as compared to single-ion complexes. The classic microscopic outersphere theory that works successfully for small molecules in understanding the transverse relaxation rate 1/T(2) is not valid for these larger and stronger magnetic spheres. We categorize the relaxation behavior of the tissue-sphere system for ferromagnetic spherical perturbers in five diffusion regimes. Over the entire range of perturber size a general understanding of the relaxation mechanisms is described in terms of basic physical features of the system, and, through empiric models, the imaging sequences of spin echo and gradient echo. The models are verified with results of our spectroscopic measurements as well as simulations and experiments in the literature. Normalized models, obtained through proper scaling of the sphere radius and the relaxation rate, can be used to quantitatively estimate 1/T(2) for various combinations of the variables. Effects of diffusion upon image contrast and effects of sphere size change upon relaxation with their possible applications in microvascular dilatation and other areas are then discussed.

Mri measurements of T1, T2 and D for gels undergoing volume phase transition.

Gels consist of crosslinked polymer network swollen in solvent. The network of flexible long-chain molecules traps the liquid medium they are immersed in. Some gels undergo abrupt volume change, a phase transition process, by swelling-shrinking in response to external stimuli changes in solvent composition, temperature, pH, electric field, etc. We report that during volume phase transition changes of NMR longitudinal relaxation time T(1), NMR transverse relaxation time T(2), and diffusion coefficient D of the PMMA gel, and D of the NIPA gel. We describe how the gels were synthesized and the reason of using the snapshot FLASH imaging sequence to measure T(1), T(2), and D. Since T(1), T(2) and D maps have identical field of view and data are extracted from identical areas from their respective maps, these values can be correlated quantitatively on a pixel-by-pixel basis. Thus a complete set of NMR parameters is measured in-situ: the gels are in their natural state, immersed in the liquid, during the phase transition. The results of spectroscopic method agree with that of snapshot FLASH imaging method. For the PMMA gel T(1), T(2) and D decrease when gels undergo volume phase transition between deuterated acetone concentration of 30% and 40%. At its contracted state, T(1) is reduced to a little less than one order of magnitude, T(2) over two orders of magnitude, and D over one order of magnitude, smaller from values of PMMA gel at the swollen state. At an elevated temperature of 54 degrees C the thermosensitive NIPA gel is at a contracted state, with its D reduced to almost one order of magnitude smaller from that of the swollen NIPA at room temperature.