We used PET scans with the tracers [18F]fluorodeoxyglucose (FDG) and [11C]raclopride (RACLO) to study glucose metabolism and dopamine D2 receptor binding in the caudate nucleus and putamen of 18 carriers of the Huntington's disease gene mutation (10 asymptomatic subjects and eight untreated symptomatic Huntington's disease patients in an early disease stage). We also performed MRI scans and measured the bicaudate ratio (BCR) in the same subjects. Data were compared with those from nine mutation-negative members of Huntington's disease families and separate groups of age matched controls. The PET scans were repeated 1.5-3 years later in six of the asymptomatic gene carriers. Symptomatic Huntington's disease patients showed a marked reduction of FDG and RACLO uptake in the caudate nucleus and putamen and a significant increase of BCR. Asymptomatic mutation carriers revealed significant hypometabolism in the caudate nucleus and putamen. The RACLO binding was significantly decreased in the putamen. Decrements of caudate nucleus tracer uptake, particularly RACLO, correlated significantly with BCR increases in both symptomatic and asymptomatic gene carriers. In asymptomatic carriers, metabolic and receptor binding decreases were also significantly associated with the CAG repeat number but not with the individual's age. Discriminant function analysis correctly classified clinical and genetic status in 24 of 27 subjects on the basis of their striatal PET values (83% sensitivity and 100% specificity). Three asymptomatic mutation carriers were classified/grouped together with mutation-negative subjects, indicating that these individuals had normal striatal RACLO and FDG uptake. Follow-up PET data from gene-positive subjects showed a significant reduction in the mean striatal RACLO binding of 6.3% per year. Striatal glucose metabolism revealed an overall non significant 2.3% decrease per year. These data indicate that asymptomatic Huntington's disease mutation carriers may show normal neuronal function for a long period of life. These findings also suggest that it may be possible to predict when an asymptomatic gene carrier will develop clinical symptoms from serial PET measurements of striatal function.

Sensitivity encoding (SENSE) offers a new, highly effective approach to reducing the acquisition time in spectroscopic imaging (SI). In contrast to conventional fast SI techniques, which accelerate k-space sampling, this method permits reducing the number of phase encoding steps in each phase encoding dimension of conventional SI. Using a coil array for data acquisition, the missing encoding information is recovered exploiting knowledge of the distinct spatial sensitivities of the individual coil elements. In this work, SENSE is applied to 2D spectroscopic imaging. In recent years, studies on the metabolism of the healthy and pathologic human brain are increasingly performed using proton magnetic resonance spectroscopic imaging (SI) (1-6). For the investigation of local metabolite concentrations, the advantage of SI over single voxel spectroscopy lies in the spatial resolution obtained by acquiring a whole grid of spectra. These spectra show only a slight reduction in the signal-to-noise ratio (SNR) per unit volume and unit time with respect to single voxel spectroscopy (7). Furthermore, displaying the resulting metabolite levels as images permits an easy comparison of local metabolism changes with other data, e.g., anatomical images and functional activation maps. The major disadvantage of standard SI techniques (8,9) is the long acquisition time of high-resolution measurements, which considerably complicates clinical application.The long acquisition time of SI measurements with two spatial dimensions arises from the large number of samples to be collected, i.e., K x ϫ K y ϫ N t samples in the two spatial dimensions and one time/spectral dimension. In conventional spectroscopic imaging k-space is sampled by acquiring N t data points in the time dimension per excitation, thus requiring K x ϫ K y excitations for a complete 2D spatial image. In the past decade, several fast SI methods have been proposed in response to this problem, which rely on sampling k-space in a more time efficient way.One fast SI technique, proposed by Duyn and Moonen (10), exploits the fact that at lower field strengths T 2 is much longer than T* 2 for the metabolites of interest, allowing one to acquire several spin-echoes per excitation, which are separately phase-encoded. The time savings achievable with this technique depend on the length of the spin-echo train, which typically ranges from 2 to 4. However, measurements with short echo spacing are not feasible with this technique, as the acquisition interval and thus the spectral resolution are limited by the echo spacing. Furthermore, acquiring multiple spin-echoes results in uneven T 2 -weighting of k-space, which adversely affects the point-spread function of the technique. Another type of fast SI technique uses readout gradients for spatial encoding. Based on an SI method originally proposed by Mansfield (11), proton echo-planar spectroscopic imaging (PEPSI) by Posse et al. (12) saves time by acquiring K x ϫ N t data points per excitation using echoplanar trajectories. A third option...

The isotope Th is the only nucleus known to possess an excited stateTh in the energy range of a few electronvolts-a transition energy typical for electrons in the valence shell of atoms, but about four orders of magnitude lower than typical nuclear excitation energies. Of the many applications that have been proposed for this nuclear system, which is accessible by optical methods, the most promising is a highly precise nuclear clock that outperforms existing atomic timekeepers. Here we present the laser spectroscopic investigation of the hyperfine structure of the doubly charged Th ion and the determination of the fundamental nuclear properties of the isomer, namely, its magnetic dipole and electric quadrupole moments, as well as its nuclear charge radius. Following the recent direct detection of this long-sought isomer, we provide detailed insight into its nuclear structure and present a method for its non-destructive optical detection.