Brain N-acetylaspartate is elevated in Pelizaeus-Merzbacher disease with PLP1 duplication.

OBJECTIVE: To assess alterations in brain metabolites of patients with Pelizaeus-Merzbacher disease (PMD) with the proteolipid protein gene 1 (PLP1) duplications using quantitative proton MRS. METHODS: Five unrelated male Japanese patients with PMD with PLP1 duplications were analyzed using automated proton brain examination with the point resolved spectroscopy technique (repetition and echo time of 5,000 and 30 msec). Localized spectra in the posterior portion of the centrum semiovale were acquired, and absolute metabolite concentrations were calculated using the LCModel. RESULTS: Absolute concentrations of N-acetylaspartate (NAA), creatine (Cr), and myoinositol (MI) were increased by 16% (p < 0.01), 43% (p < 0.001), and 31% (p < 0.01) in patients with PMD as compared with age-matched controls. There was no statistical difference in choline concentration. CONCLUSION: The increased concentration of NAA, which could not be detected by previous relative quantitation methods, suggests two possibilities: axonal involvement secondary to dysmyelination, or increased cell population of oligodendrocyte progenitors. Elevated Cr and MI concentrations may reflect the reactive astrocytic gliosis. Our study thus emphasizes the importance of absolute quantitation of metabolites to investigate the disease mechanism of the dysmyelinating disorders of the CNS.

An asymmetric slice profile: spatial alteration of flow signal response in 3D time-of-flight NMR angiography.

We introduce an asymmetric slice profile technique, which alters the spatial response of the flow signal in 3D time-of-flight NMR angiography. By gradually increasing the flip angle from the inflow to the outflow portions of the slab, the inflow refreshment effect is distributed over a wide slab thickness. The asymmetric slice profile is simply produced by using a Gaussian RF excitation with an overlapping presaturation. The spatial distribution of steady flow signal in a phantom study demonstrated an essential agreement with a numerical simulation. 3D time-of-flight NMR angiography of volunteers' heads using this technique provided a smooth vascular depiction over a wide slab thickness.

Influence of matrix size, vessel shape, vascular diameter, flow velocity, course of vessels on MR angiography.

Basic experiments were done to examine the influence of the extent of curve, direction of flow, vascular diameter, velocity of flow, and course of vessels on MR angiography. In the first experiment, two phantoms were constructed of vinyl tubing, a hairpin type and one with tubes bent to varying degrees. These phantoms were imaged in two matrices, different FOV, and of various velocities with a 1.5 Tesla system. Images of a normal volunteer were also obtained. In studies of the hairpin phantoms, a low intensity artifact appeared at the curve position, and the edge became fuzzy when the flow was perpendicular to the phase encoding direction. These phenomena were more apparent with a smaller matrix, smaller FOV, more gentle angle, larger diameter, and faster flow; in other words the component along the direction was dominant. In the phantom that used bent tubes, another low intensity artifact appeared on the medial side of the outflow portion. The results obtained from the volunteer corresponded well to those from the basic experiments. It was thought that the profile of flow was not well demonstrated due to the coarse matrix. In the second experiment, water flowed at various speeds through three-dimensional phantoms that were made of vinyl tubes of various diameters and directions. The phantoms were imaged with two- and three-dimensional time of flight and phase contrast angiography. The lower limits of detection of the phase contrast method were almost the same. In the coronal plane, the lower limit decreased to 2.5 mm for arteries and 9.5 mm for veins.(ABSTRACT TRUNCATED AT 250 WORDS)

[Dynamic motion study of the cervical spine using ultra-fast gradient echo with RF-spoiled GRASS--evaluation of cervical instability].

In order to assess the instability of the cervical spine, ten patients with cervical spondylosis were studied by dynamic MRI using Ultra-Fast RF-Spoiled GRASS which is capable of subsecond imaging. Dynamic MRI has proved to be useful in the evaluation of cervical instability, especially in detecting the transient abnormal mobility of cervical spines which cannot be identified on conventional radiography.

Multiple echo SSFP sequences.

We report a new type of SSFP imaging sequences for acquiring higher-order echoes. Spins excited during a cycle have, in a sense, a phase memory such that they can be refocused several cycles down the line, and since the spins are pulsed under a steady-state condition, the resulting echoes have very complicated T1 and T2 dependencies. A steady-state equation, which describes the T1 and T2 dependencies for the higher-order echoes, is presented, and the intensity of each echo is calculated and compared with the experimental results. Although the signal intensity of the higher-order echoes are weaker than the FID or the CE-FAST echo, these echoes may be used to obtain images with different contrast dependencies previously unobtainable with either of the two signals.

Time-resolved magnetic resonance angiography.

A time-resolved phase contrast magnetic resonance angiography technique is described. This technique provides a series of angiograms obtained at different phases of the cardiac cycle. Such a series of angiograms can be used to evaluate blood flow dynamics. For example, turbulent flow in the regions of vessel bifurcations is easily demonstrated and followed during systole and diastole. Retrograde flow can also be observed. Dynamic angiography can be particularly useful in distinguishing transient image features, such as signal voids due to turbulent flow, from static features arising from vessel morphology.