@misc{9248507,
  abstract     = {{BACKGROUND AND PURPOSE
The amino acid glutamate (Glu) is the primary excitatory neurotransmitter in human brain and is
involved in both synaptic transmission as well as metabolic pathways. Dysfunction of glutamate
concentration in the brain has been implicated in neurological diseases, such as epilepsy, Alzheimer’s
disease, schizophrenia and essential tremor. Non-invasive detection of glutamate concentration using
the novel MRI technique named chemical exchange saturation transfer (CEST) was demonstrated in
2012 and it displays a superior spatial resolution and signal-to-noise ratio (SNR) compared to standard
proton magnetic resonance spectroscopy (1H MRS). Glutamate-weighted CEST imaging require
ultra-high magnetic field strength (≥ 7 T) and results have shown a high degree of reproducibility in
healthy volunteers at 7 T.
The aim of this master’s project is to implement GluCEST imaging at the National 7 T facility in Lund
and to detect glutamate concentration in phantoms as well as in healthy volunteers.

THEORY AND METHODS
Glutamate is indirectly detected by saturating protons in the glutamate amino group with a frequency
selective radiofrequency (RF) pulse, which then transfers to surrounding water through so called
chemical exchange. The resulting decrease in water signal, the so called CEST effect, has a strong pH
and RF pulse shape dependency.
A sequence designed for CEST imaging was modified under a research agreement on the Philips 7 T
Achieva magnetic resonance imaging (MRI) system in Lund. The CEST effect detected by the
sequence was investigated using three phantoms with different pH-values and Glu concentrations, as
well as varying RF amplitudes and durations for each phantom.
Subsequently, three healthy volunteers were scanned using the RF pulse parameters that maximised
CEST effect without exceeding specific absorption rate (SAR) restrictions, as determined from the
phantom experiments.

RESULTS AND DISCUSSION
Phantom measurements displayed higher CEST effect at the resonance frequency of the glutamate amine
(3 parts-per million (ppm) downfield from bulk water) for lower pH-values and a proportionality to RF
amplitude and duration. These results concur with previous studies and indicate that Philips CEST
sequence is able to perform GluCEST imaging on a 7 T MRI system.
Noticeable effect from radiofrequency magnetic field (B1) inhomogeneity was observed in GluCEST
images, both in phantoms and healthy volunteers, highlighting the need for post-process B1 correction.
A strong contribution from nuclear Overhauser enhancement (nOe) was observed in healthy volunteers,
resulting in images with negative values which was not expected. However, a CEST effect was observed
at frequency 3 ppm downfield from bulk water and expected contrast between brain tissues were visible.

CONCLUSIONS
Measurements of Glu in phantoms and healthy volunteers were possible using Philips CEST sequence,
but required robust post-processing for B0 and B1 inhomogeneities. For further work, developing a
method for B1 correction is suggested and investigating the possibility of expanding single-slice into
volumetric imaging is recommended for future applications.}},
  author       = {{Pettersson, Emma}},
  language     = {{eng}},
  note         = {{Student Paper}},
  title        = {{Detection of the Excitatory Neurotransmitter Glutamate in the Human Brain Using Glutamate-CEST at Ultra-High Magnetic Field Strength (7 T)}},
  year         = {{2026}},
}