Magnetic resonance imaging echo time

Human skin is the largest organ in the human body. It is fundamentally important to health as the semi-permeable barrier - the first line of defence - between the body and the external world. However, it remains relatively inaccessible to conventional magnetic resonance imaging, firstly because it is thin and therefore requires high spatial resolution, and secondly because it is characterized by relatively short T2 relaxation times, particularly in the outermost stratum comeum. Conventional studies have not usually achieved a resolution better than 70-150 pm, with an echo time of the order of a millisecond or so. As a planar sample, skin has proved amenable to GARField study where it has been possible to use both a shorter echo time and achieve a better spatial resolution, albeit in one direction only. Such studies have attracted the interest of the pharmaceutical and cosmetic industries that are interested in skin hydration and the transport of creams and lotions across the skin. 

As I look back at this experience, it was an awesome adventure to be alone, during and for an interval of time after this discovery, with the apparatus showing one new effect after another, when there was no one in the Illinois Physics Department experienced in NMR with whom I could talk. Little did the early NMR resonance community realize that the analogue of spin echo hidden memory contained in excited phases of all kinds of states of matter, including plasmas, would be obtained in the future by use of optical laser, electric, and acoustic pulses as well. And now today the use of spin echoes is a standard procedure for magnetic resonance imaging of the human body for medical diagnosis. 

Figure 4 A series of magnetic resonance imaging scans obtained through the left thigh of a New Zealand white rabbit bearing a V2 carcinoma before (A), immediately after (B), and 3jh after (C) the administration of 5 jimol/kg of PCI-0101 (complex 2 bisacetate counter anions). Noteworthy is the persistent, marked increase in contrast enhancement of the V2 carcinoma compared with surrounding muscle obtained under these conditions (1.5T T,-weighted pulsing sequence 300/15 repetition time/echo time). Reproduced from [26] by permission of Lippincott-Raven Publishers...

Figure 7 A P MRS spectrum from neonatal brain at 2.4T. A 125 ml VOI, localized using PRESS, was centered on the thalami. Acquisition parameters were TE 10 ms repetition time 12 s 160 averaged echoes. The numbered peaks are 1 PME 2 extracellular and intracellular Pi 3 glycerolphosphorylethanolamine and GPC 4 PCr 5, 6, and 8 y-, a-, and -NTP 7 nicotinamide dinucleotides and uridine diphosphosugars. (Reproduced with permission from Cady EB, Wylezinska M, Penrice J, Lorek A, and Amess P (1996) Quantitation of phosphorus metabolites in newborn human brain using internal water as a reference standard. Magnetic Resonance Imaging 14(3) 293-304 Elsevier.)...

Fig. 1.34. Basic Stejskal-Tanner pulsed gradient spin-echo (PGSE) pulse sequence n/2-g 8)-n-g(<5)-echo used for displacement spectroscopy. The echo time TE is 2r and the displacement time is A. After Hills [718]. Reprinted from B. Hills, Magnetic Resonance Imaging in Food Science, John Wiley Sons, Inc., New York, NY. Copyright (1998, John Wiley Sons, Inc.). This material is used by permission of John Wiley Sons, Inc.

Simister, R. J., Woermann, F. G., McLean, M. A. et al. A short-echo-time proton magnetic resonance spectroscopic imaging study of temporal lobe epilepsy. Epilepsia 43 1021-1031, 2002. 

Hwang JH, Graham GD, Behar KL, Alger JR, Prichard JW, et al. 1996. Short echo time proton magnetic resonance spectroscopic imaging of macromolecule and metabolite signal intensities in the human brain. Magn Reson Med 35 633-639. 

Figure 5 Two images (256 pixels of (10 pm), slice thickness 500 pm) obtained with the spin-echo pulse sequence of Figure 2 from a geranium stem in which different read gradients and echo times are employed (A) 20 kHz with = 13.5 ms (B) 100 kHz with Te = 3.2 ms. Reprinted with permission from Rofe CJ, Van Noort J, Back PJ and Callaghan PT (1995) Journal of Magnetic Resonance 6108 125-136.

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