Terahertz pulsed imaging of basal cell carcinoma ex vivo and in vivo.

BACKGROUND: Terahertz radiation lies between the infrared and microwave regions of the electromagnetic spectrum and can be used to excite large amplitude vibrational modes of molecules and probe the weak interactions between them. Terahertz pulsed imaging (TPI) is a noninvasive imaging technique that utilises this radiation. OBJECTIVES: To determine whether TPI could differentiate between basal cell carcinoma (BCC) and normal tissue and to test whether it can help facilitate delineation of tumour margins prior to surgery. METHODS: A portable TPI system was used in the clinic to image 18 BCCs ex vivo and five in vivo. RESULTS: The diseased tissue showed a change in terahertz properties compared with normal tissue, manifested through a broadening of the reflected terahertz pulse. Regions of disease identified in the terahertz image correlated well with histology. CONCLUSIONS: This study has confirmed the potential of TPI to identify the extent of BCC in vivo and to delineate tumour margins. Further clinical study of TPI as a surgical tool is now required.

Mechanism of THz emission from asymmetric double quantum wells.

Impulsive interband optical excitation of the lowest two conduction subbands of a suitably engineered GaAs/AlGaAs double quantum well can lead to coherent THz emission. We demonstrate that, contrary to previous expectations, the dominant emission mechanism can involve the beating of either continuum or exciton states, depending on excitation conditions. The coherence of the continuum beats persists for several picoseconds even for excitation an optical phonon energy above the band edge. We attribute this to the small energy difference between the component eigenstates, which substantially reduces the number of relevant scattering events.

Experimental allergic encephalomyelitis in non-human primates: MRI and MRS may predict the type of brain damage.

Volume-localized proton spectroscopy and T2-weighted MRI were performed on 23 monkeys with experimental allergic encephalomyelitis (EAE). The purpose of this study was to determine the relationships between temporal changes in lesion activity (measured on T2-weighted MRI), MRS [N-acetyl aspartate (NAA), creatine (CR), choline (CHO)], and the histologic definition of disease determined post-mortem. Animals were scanned in the same areas of the brain once a week before and after sensitization to myelin basic protein (BP). Histologic lesion types were predicted by a combination of preceding MRI and MRS measurements. Acutely fatal EAE lesions were large and monophasic as visualized by MRI, and increased CHO (p < 0.02, n = 16) and CHO/CR ratio (p < 0.001, n = 16) were detected by MRS at disease onset. Chronic EAE lesions were preceded by multiple inflammatory attacks as visualized by MRI and consistently low levels of NAA (p < 0.02, n = 13) and NAA/CR (p < 0.01, n = 13) which occurred after the initial attack. MRI negative brain regions (from animals that were sensitized to BP) were associated with low CHO/CR (p < 0.1, n = 5). The temporal correlation of MRI lesion activity and absolute MRS proton metabolites shows promise for predicting the subsequent duration and histologic type of lesions in EAE in non-human primates.