Purpose: To design and compare an eight-channel phased array (PA) coil for carotid imaging to an established fourchannel PA design at 3T. Materials and Methods:An eight-channel PA (8PA) coil was designed specifically for imaging the carotid bifurcation and compared with the existing four-channel (4PA) design using a phantom and by in vivo black-blood magnetic resonance imaging (MRI). The 8PA and 4PA were compared in terms of coverage, signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR). Results:The 8PA showed up to 1.7-fold improvement in SNR at a depth of 3.5 cm and greater longitudinal coverage at a given SNR on a phantom. The 8PA showed improved vessel wall SNR for high spatial resolution (0.63 mm 2 ) PD, T1, and T2 (1.7, 1.7, 1.6 times, respectively; P Յ 0.002) and improved CNR (1.7, 1.6, 1.5 times, respectively; P Յ 0.002). Ultrahigh-resolution (0.27 mm 2 ) T1-weighted images showed better SNR and CNR (1.4 times, P Յ 0.0001) on 8PA compared to 4PA. Conclusion:Carotid imaging studies may benefit from the improved SNR and larger coverage provided by use of the 8PA.

Approximately 1% of the Xenopus laevis genome consists of highly repetitive DNA known alternatively as OAX (for Oocyte Activation in Xenopus), Satellite I, or Repetitive HindIII Monomer 2. Present as tandemly repeated units of approximately 750 base pairs, OAX encodes a family of small RNA species transcribed by RNA polymerase III. Although the subject of many of the classic studies on early embryonic gene regulation, reports on OAX expression remain contradictory and incomplete. Using whole-mount in situ hybridization and RNase protection assays, we have therefore examined in detail the expression pattern of OAX in Xenopus embryos of various stages. OAX is initially expressed during gastrula stages; by tailbud stages embryos display discrete zones of expression at the dorsal boundary of the cement gland, in the developing somites and differentiating skeletal muscle, as well as in the dorsal aspect of the neural tube. These data demonstrate that OAX is expressed in a dynamic pattern under tight spatial and temporal regulation.

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