Task Activation Results in Regional 13 C-Lactate Signal Increase in the Human Brain.

Hyperpolarized- 13 C magnetic resonance imaging (HP- 13 C MRI) was used to image changes in 13 C-lactate signal during a visual stimulus condition in comparison to an eyes-closed control condition. Whole-brain 13 C-pyruvate, 13 C-lactate and 13 C-bicarbonate production was imaged in healthy volunteers (N=6, ages 24-33) for the two conditions using two separate hyperpolarized 13 C-pyruvate injections. BOLD-fMRI scans were used to delineate regions of functional activation. 13 C-metabolite signal was normalized by 13 C-metabolite signal from the brainstem and the percentage change in 13 C-metabolite signal conditions was calculated. A one-way Wilcoxon signed-rank test showed a significant increase in 13 C-lactate in regions of activation when compared to the remainder of the brain ( p = 0.02, V = 21). No significant increase was observed in 13 C-pyruvate ( p = 0.11, V = 17) or 13 C-bicarbonate ( p = 0.95, V = 3) signal. The results show an increase in 13 C-lactate production in the activated region that is measurable with HP- 13 C MRI.

Evidence of 13 C-lactate oxidation in the human brain from hyperpolarized 13 C-MRI.

PURPOSE: To test the hypothesis that lactate oxidation contributes to the 13 $$ {}^{13} $$ C-bicarbonate signal observed in the awake human brain using hyperpolarized 13 $$ {}^{13} $$ C MRI. METHODS: Healthy human volunteers (N = 6) were scanned twice using hyperpolarized 13 $$ {}^{13} $$ C-MRI, with increased radiofrequency saturation of 13 $$ {}^{13} $$ C-lactate on one set of scans. 13 $$ {}^{13} $$ C-lactate, 13 $$ {}^{13} $$ C-bicarbonate, and 13 $$ {}^{13} $$ C-pyruvate signals for 132 brain regions across each set of scans were compared using a clustered Wilcoxon signed-rank test. RESULTS: Increased 13 $$ {}^{13} $$ C-lactate radiofrequency saturation resulted in a significantly lower 13 $$ {}^{13} $$ C-bicarbonate signal (p = 0.04). These changes were observed across the majority of brain regions. CONCLUSION: Radiofrequency saturation of 13 $$ {}^{13} $$ C-lactate leads to a decrease in 13 $$ {}^{13} $$ C-bicarbonate signal, demonstrating that the 13 $$ {}^{13} $$ C-lactate generated from the injected 13 $$ {}^{13} $$ C-pyruvate is being converted back to 13 $$ {}^{13} $$ C-pyruvate and oxidized throughout the human brain.

Age-associated change in pyruvate metabolism investigated with hyperpolarized 13 C-MRI of the human brain.

In this study, hyperpolarized 13 C MRI (HP-13 C MRI) was used to investigate changes in the uptake and metabolism of pyruvate with age. Hyperpolarized 13 C-pyruvate was administered to healthy aging individuals (N = 35, ages 21-77) and whole-brain spatial distributions of 13 C-lactate and 13 C-bicarbonate production were measured. Linear mixed-effects regressions were performed to compute the regional percentage change per decade, showing a significant reduction in both normalized 13 C-lactate and normalized 13 C-bicarbonate production with age: - 7 % ± 2 % per decade for 13 C-lactate and - 9 % ± 4 % per decade for 13 C-bicarbonate. Certain regions, such as the right medial precentral gyrus, showed greater rates of change while the left caudate nucleus had a flat 13 C-lactate versus age and a slightly increasing 13 C-bicarbonate versus age. The results show that both the production of lactate (visible as 13 C-lactate signal) as well as the consumption of monocarboxylates to make acetyl-CoA (visible as 13 C-bicarbonate signal) decrease with age and that the rate of change varies by brain region.

Total skin electron therapy vertical profiles measured using radiochromic film.

BACKGROUND: Vertical dose profiles of Total Skin Electron Therapy (TSET) electron fields are often measured using ionization chambers (ICs); however, resulting protocols are tedious and time consuming due to complex gantry arrangements, numerous point dose measurements and extra-cameral corrections. This inefficiency is reduced when using radiochromic film (RCF) dosimetry through simultaneous dose sampling and the elimination of IC-related measurement corrections. PURPOSE: To investigate the feasibility of RCF dosimetry for TSET vertical profile measurements and establish a novel RCF based vertical profile quality assurance protocol. METHODS: Thirty-one vertical profiles were measured using GAFChromic® EBT-XD RCF on two matched linear accelerators (linacs) over 1.5 years. Absolute dose was quantified using a triple channel calibration method. Two IC profiles were collected for comparison to RCF profiles. Twenty-one archived IC measured profiles from two different matched linacs from 2006 to 2011 were analyzed. Inter- and intra-profile dose variability was compared between dosimeters. The time required for the RCF and IC protocols was compared. RESULTS: RCF measured inter-profile variability ranged from 0.66%-5.16% and 1.30%-3.86% for the two linacs. A 0.2%-5.4% inter-profile variability was observed for archived IC measured profiles. RCF measured intra-profile variability ranged from 10.0%-15.8%; six of 31 profiles exceeded the EORTC ± 10% limit. Archived IC measured profiles exhibited lower intra-profile variability (4.5%-10.4%). RCF and IC measured profiles agreed in the center of the field; however, RCF doses measured 170-179 cm above the TSET treatment box base were ∼7% greater. Modification to the RCF phantom eliminated this discrepancy, resulting in comparable intra-profile variability and agreeance with the ±10% limit. Measurement times were reduced from 3 h (IC protocol) to 30 min (RCF protocol). CONCLUSIONS: RCF dosimetry improves protocol efficiency. RCF has been established as a valuable dosimeter for TSET vertical profile quantification when compared to ICs as the gold standard.