Kim Annink

221 Measurement of brain temperature using MRS With phantom measurement in our 3.0T MR scanner, we also calibrated a new formula specific for our scanner, referred to as the calibrated formula, to validate the formula of Wu et al (8). A small, in-house developed, spherical phantom with a diameter of approximately 3 cm containing a water solution with creatine, GABA, glutamate, glutamine and NAA with a pH of 7.4 was used. Temperature was measured continuously by securing a Neoptix fiber optic sensor on top of the phantom (Neoptix, Qualitrol Company LLC of Fairport, NY, USA). The phantom was heated in a water bath until the temperature was 45 °C. Thereafter, the phantom was wrapped in towels to slow down the cooling process. The phantom was placed in the isocenter of the MRI and during cooling (from 43 to 30 °C), 20 1 H-MRS scans were conducted using long and short TE alternating. By analyses of the ΔH 2 O-NAA and actual measured temperature, a new formula was developed. This formula was compared to the formula of Wu et al. to assess whether the two formulas differed (8). MRI acquisition and brain temperature calculation MRI examinations were conducted using a 1.5T or 3.0T Achieva scanner (Philips Medical Systems, Best, the Netherlands). As standard of care, all infants with NE who were treated with hypothermia underwent cerebral MRI within the first week after birth with a duration of 30 to 45 minutes. All neonates were scanned in a vacuum mattress to prevent movement artefacts (Med Vac Infant Immobilizer Bag, Radstadt, Austria). During the MRI, the heart rate and oxygen saturation was measured with a pulse oximeter (Nonin, Minneapolis, MN) and respiration rate was observed using the standard Philips equipment (Philips Medical Systems, Best, Netherlands). Scan protocols included, among others, single voxel 1 H-MRS (PRESS, repetition time=2000ms, TE=36ms (short TE) and/or 288ms (long TE), phase cycles=16, 64 measurements, voxel sizes varied between 10x10x10mm and 20x10x10mm, water suppression method = “excitation” (2-water selective pulses followed by spoilers). The region of interest (ROI) for single voxel 1 H-MRS was the left deep grey matter, according to Alderliesten et al. (15). The quality of the spectra was visually inspected (visual estimation signal to noise ratio (SNR) of NAA peak should be larger than 3 and measurement of line width should be lower than 10Hz, Figure 1) and spectra with poor quality i.e. low SNR or clear artefacts from water suppression were excluded. If the quality was sufficient, jMRUI software version 5.2 was used to analyze the spectrum (16). The peak of NAA 10