With primitive approaches, the diagnosis and therapy were operated at the cellular, molecular, or even at the genetic level. As the diagnostic techniques are more concentrated towards molecular level, multi modal imaging becomes specifically essential. Multi-modal imaging has extensive applications in clinical as well as in pre-clinical studies. Positron Emission Tomography (PET) has flourished in the field of nuclear medicine, which has motivated it to fuse with Computed Tomography (CT) and Magnetic Resonance Imaging (MRI) for PET/CT and PET/MRI respectively. However, the challenges in PET/CT are due to the inability of simultaneous acquisition and reduced soft tissue contrast, which has led to the development of PET/MRI. Also, MRI offers the better soft tissue contrast over CT. Hence, fusion of PET and MRI results in combining structural information with functional image from PET. Yet, it has many technical challenges due to the interference between the modalities. Also, it must be resolved with various approaches for addressing the shortcomings of each system and improvise on the image quantification system. This review elaborates on the various challenges in the present PET/MRI system and the future directions of the hybrid modality. Also, the different data acquisition and analysis techniques of PET/MRI system are discussed with enhanced details on the software tools.
Liquid secondary ionization mass spectrometry (LSIMS) operating in the positive- and negative-ion modes was used to study fragmentation profiles and to obtain the amino acid sequences of a set of seven phosphoenkephalin peptides. The use of glycerol as the liquid matrix led to increase in fragmentation of phosphopeptides. The prominent amino acid sequence-determining ions in the positive-ion mode are y-type C-terminal ions; the N-terminal sequence-specific ions are observed sporadically. The most dominant ions in those mass spectra, however, are the immonium ions and a few low-mass side-chain cleavage products. The mass spectra in the negative-ion mode are more information-rich, and provide data complementary to that from the positive-ion mode. The phosphate group marker ions, m/z 79 (PO-3) and 97 (H2PO-4), are prominent and both N- and C-termini sequence ions are formed with equal facility in this mode of analysis. Both positive- and negative-ion mass spectral data are useful in determining the amino acid sequence of all the seven phosphoenkephalins. Thus, LSIMS alone can be a viable option to the tandem mass spectrometry approach when sufficient quantities (> 50 nmol) of phosphopeptides are available.
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