Changes in cerebral blood flow (CBF) in response to hypercapnia induced changes in vascular tone, known as cerebrovascular reactivity (CVR), can be measured using the Blood Oxygenation Level ...Dependent (BOLD) MR contrast. We examine regional differences in the BOLD-CVR response to a progressively increasing hypercapnic stimulus as well as regional BOLD characteristics for the return to baseline normocapnia. CVR across 9 subjects was highest in the cerebral lobes and deep gray matter. Peak CVR in these regions was measured at 3.6±1.6mmHg above baseline end-tidal CO2. White matter CVR was generally reduced compared to that of the gray matter (peak white matter CVR was ~48% lower). A positive relationship between the end-tidal CO2 value at which peak CVR was measured and white matter depth is observed. Furthermore, the time required for the BOLD signal to return to baseline after cessation of the hypercapnic stimulus, was also related to white matter depth; the return, expressed as a time constant, was ~25% longer in white matter. To explain the observed differences in regional CVR response, a model is proposed that takes into account the local architecture of the cerebrovascular, which can result in changes in regional blood flow distribution as a function of end-tidal CO2.
Gadolinium-based contrast agents (GBCAs) are widely used in MRI, despite safety concerns regarding deposition in brain and other organs. In animal studies gadolinium was detected for weeks after ...administration in the kidneys, but this has not yet been demonstrated in humans.
To find evidence for the prolonged presence of gadobutrol in the kidneys in healthy volunteers.
Combined retrospective and prospective analysis of a repeatability study.
Twenty-three healthy volunteers with normal renal function (12 women, age range 40-76 years), of whom 21 were used for analysis.
Inversion recovery-based T
map at 3T.
T
maps were obtained twice with a median interval of 7 (range: 4-16) days. The T
difference (ΔT
) between both scans was compared between the gadolinium group (n = 16, 0.05 mmol/kg gadobutrol administered after T
mapping during both scan sessions) and the control group (n = 5, no gadobutrol). T
maps were analyzed separately for cortex and medulla.
Mann-Whitney U-tests to detect differences in ΔT
between groups and linear regression to relate time between scans and estimated glomerular filtration rate (eGFR) to ΔT
.
ΔT
differed significantly between the gadolinium and control group: median ΔT
cortex -98 vs. 7 msec (P < 0.001) and medulla -68 msec vs. 19 msec (P = 0.001), respectively. The bias corresponds to renal gadobutrol concentrations of 8 nmol/g tissue (cortex) and 4 nmol/g tissue (medulla), ie, ~2.4 μmol for both kidneys (0.05% of original dose). ΔT
correlated in the gadolinium group with duration between acquisitions for both cortex (regression coefficient (β) 16.5 msec/day, R
0.50, P < 0.001) and medulla (β 11.5 msec/day, R
0.32, P < 0.001). Medullary ΔT
correlated with eGFR (β 1.13 msec/(ml/min) R
0.25, P = 0.008).
We found evidence of delayed renal gadobutrol excretion after a single contrast agent administration in subjects with normal renal function. Even within this healthy population, elimination delay increased with decreasing kidney function.
3 Technical Efficacy: Stage 3 J. Magn. Reson. Imaging 2020;52:622-631.
Blood Oxygenation Level Dependent (BOLD) imaging in combination with vasoactive stimuli can be used to probe cerebrovascular reactivity (CVR). Characterizing the healthy, age-related changes in the ...BOLD-CVR response can provide a reference point from which to distinguish abnormal CVR from the otherwise normal effects of ageing. Using a computer controlled gas delivery system, we examine differences in BOLD-CVR response to progressive hypercapnia between 16 young (28±3years, 9 female) and 30 elderly subjects (66±4years, 13 female). Furthermore, we incorporate baseline T2* information to broaden our interpretation of the BOLD-CVR response. Significant age-related differences were observed. Grey matter CVR at 7mmHg above resting PetCO2 was lower amongst elderly (0.19±0.06%ΔBOLD/mmHg) as compared to young subjects (0.26±0.07%ΔBOLD/mmHg). White matter CVR at 7mmHg above baseline PetCO2 showed no significant difference between young (0.04±0.02%ΔBOLD/mmHg) and elderly subjects (0.05±0.03%ΔBOLD/mmHg). We saw no significant differences in the BOLD signal response to progressive hypercapnia between male and female subjects in either grey or white matter. The observed differences in the healthy BOLD-CVR response could be explained by age-related changes in vascular mechanical properties.
•We explore the age-dependent BOLD-CVR response to progressive hypercapnia.•We find age-dependent differences in the BOLD-CVR response amplitude and shape.•Age-dependent differences in baseline hemodynamic parameters are considered.•We explain differences in the context vascular mechanical properties.
High field MRI is beneficial for chemical exchange saturation transfer (CEST) in terms of high SNR, CNR, and chemical shift dispersion. These advantages may, however, be counter‐balanced by the ...increased transmit field inhomogeneity normally associated with high field MRI. The relatively high sensitivity of the CEST contrast to B1 inhomogeneity necessitates the development of correction methods, which is essential for the clinical translation of CEST. In this work, two B1 correction algorithms for the most studied CEST effects, amide‐CEST and nuclear Overhauser enhancement (NOE), were analyzed. Both methods rely on fitting the multi‐pool Bloch‐McConnell equations to the densely sampled CEST spectra. In the first method, the correction is achieved by using a linear B1 correction of the calculated amide and NOE CEST effects. The second method uses the Bloch‐McConnell fit parameters and the desired B1 amplitude to recalculate the CEST spectra, followed by the calculation of B1‐corrected amide and NOE CEST effects. Both algorithms were systematically studied in Bloch‐McConnell equations and in human data, and compared with the earlier proposed ideal interpolation‐based B1 correction method. In the low B1 regime of 0.15–0.50 μT (average power), a simple linear model was sufficient to mitigate B1 inhomogeneity effects on a par with the interpolation B1 correction, as demonstrated by a reduced correlation of the CEST contrast with B1 in both the simulations and the experiments.
At a B1 of 0.43 μT, a linear B1 correction algorithm sufficiently reduced B1 inhomogeneity effects for both amide and NOE CEST. The image quality produced by the linear correction is similar to that of the interpolation‐based B1 correction.
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