Clinical utility of brain MRS imaging of patients with adult-onset non-cirrhotic hyperammonemia

Adult-onset non-cirrhotic hyperammonemia (NCH) is a rare, but often fatal condition that can result in both reversible and irreversible neurological defects. Here we present five cases of adult-onset non-cirrhotic hyperammonemia wherein brain magnetic resonance spectroscopy (MRS) scans for cerebral glutamine (Gln) and myo-inositol (mI) levels helped guide clinical management. Specifically, we demonstrate that when combined with traditional brain magnetic resonance imaging (MRI) scans, cerebral Gln and mI MRS can help disentangle the reversible from irreversible neurological defects associated with hyperammonemic crisis. Specifically, we demonstrate that whereas an elevated brain MRS Gln level is associated with reversible neurological defects, markedly low mI levels are associated with a risk for irreversible neurological defects such as central pontine myelinolysis. Overall, our findings indicate the utility of brain MRS in guiding clinical care and prognosis in patients with adult-onset non-cirrhotic hyperammonemia.

Brain MRS glutamine as a biomarker to guide therapy of hyperammonemic coma

Acute idiopathic hyperammonemia in an adult patient is a life-threatening condition often resulting in a rapid progression to irreversible cerebral edema and death. While ammonia-scavenging therapies lower blood ammonia levels, in comparison, clearance of waste nitrogen from the brain may be delayed. Therefore, we used magnetic resonance spectroscopy (MRS) to monitor cerebral glutamine levels, the major reservoir of ammonia, in a gastric bypass patient with hyperammonemic coma undergoing therapy with N-carbamoyl glutamate and the ammonia-scavenging agents, sodium phenylacetate and sodium benzoate. Improvement in mental status mirrored brain glutamine levels, as coma persisted for 48h after plasma ammonia normalized. We hypothesize that the slower clearance for brain glutamine levels accounts for the delay in improvement following initiation of treatment in cases of chronic hyperammonemia. We propose MRS to monitor brain glutamine as a noninvasive approach to be utilized for diagnostic and therapeutic monitoring purposes in adult patients presenting with idiopathic hyperammonemia.

Spectral improvement by fourier thresholding of in vivo dynamic spectroscopy data

PURPOSE

MR spectroscopy (MRS) typically requires averaging of multiple acquisitions to achieve adequate signal-to-noise ratio (SNR). In systems undergoing dynamic changes this can compromise the temporal resolution of the measurement. One such example is (31) P MRS of exercising skeletal muscle. Spectral improvement by Fourier thresholding (SIFT) offers a way of suppressing noise without averaging. In this study, we evaluate the performance of SIFT in healthy subjects and clinical cases.

METHODS

(31) P MRS of the calf or thigh muscle of subjects (n = 12) was measured continuously before, during, and after exercise. The data were processed conventionally and with the addition of SIFT before quantifying peak amplitudes and frequencies. The postexercise increase in the amplitude of phosphocreatine was also characterized by fitting with an exponential function to obtain the recovery time constant.

RESULTS

Substantial reductions in the uncertainty of peak fitting for phosphocreatine (73%) and inorganic phosphate (60%) were observed when using SIFT relative to conventional processing alone. SIFT also reduced the phosphocreatine recovery time constant uncertainty by 38%.

CONCLUSION

SIFT considerably improves SNR, which improved quantification and parameter estimation. It is suitable for any type of time varying MRS and is both straightforward and fast to apply. Magn Reson Med 76:978-985, 2016. © 2015 Wiley Periodicals, Inc.

Metabolic imaging of mild traumatic brain injury

Traumatic brain injury results in a metabolic cascade of changes that occur at the molecular level, invisible to conventional imaging methods such as computed tomography or magnetic resonance imaging. Non-invasive metabolic imaging tools such as single photon emission computed tomography (SPECT), positron emission tomography (PET), and magnetic resonance spectroscopy (MRS) are the ideal methods for providing insight to these changes by measuring regional cerebral blood flow, glucose metabolism, and brain metabolite concentrations, respectively, after mild traumatic brain injury (mTBI). The purpose of this review is to provide an overview of the different methodologies and provide an up-to-date summary of recent findings with SPECT, PET, and MRS technologies, specifically after mTBI, as defined by standardized criteria. Given that the different physiological and pathological responses are heterogeneous, efforts will be made to separate studies at different time points after injury (acute, subacute, and chronic stages) as well as to the different types of mTBI such sports-related head injury where repetitive head injuries are much more common and may present a unique signature.