N Zoelch

Elucidation of the downfield spectrum of human brain at 7 T using multiple inversion recovery delays and echo times.

To characterize the downfield spectrum at 5–10 ppm in the human brain at a high magnetic field of 7 T. Knowledge of relaxation parameters is of interest for spectroscopy as well as chemical exchange–dependent saturation transfer experiments.

Postmortem 1 H-MRS—Detection of Ketone Bodies and Glucose in Diabetic Ketoacidosis

Diabetic ketoacidosis (DKA) is a metabolic complication of diabetes mellitus that takes a lethal course if untreated. In this way relevant to forensic medicine, secure diagnosis of DKA usually involves the evidence of elevated levels of glucose and the ketone bodies acetone, acetoacetate, and β-hydroxybutyrate in corpse fluids. We conducted a postmortem hydrogen proton magnetic resonance spectroscopy (1H-MRS) in a case of lethal DKA. Distinctive resonances of all three ketone bodies as well as glucose were visible in spectra of cerebrospinal fluid, vitreous humor, and white matter. Estimated concentrations of ketone bodies and glucose supported the findings both of autopsy and biochemical analysis. Advantages of human postmortem 1H-MRS are the lack of movement and flow artifacts as well as lesser limitations of scan duration. Postmortem 1H-MRS is able to non-invasively measure concentrations of glucose and ketone bodies in small volumes of various regions of the brain. It may thus become a diagnostic tool for forensic investigations by quick determination of pathological metabolite concentrations in addition to conventional autopsy.

Accurate determination of brain metabolite concentrations using ERETIC as external reference

Magnetic Resonance Spectroscopy (MRS) can provide in vivo metabolite concentrations in standard concentration units if a reliable reference signal is available. For 1H MRS in the human brain, typically the signal from the tissue water is used as the (internal) reference signal. However, a concentration determination based on the tissue water signal most often requires a reliable estimate of the water concentration present in the investigated tissue. Especially in clinically interesting cases, this estimation might be difficult. To avoid assumptions about the water in the investigated tissue, the Electric REference To access In vivo Concentrations (ERETIC) method has been proposed. In this approach, the metabolite signal is compared with a reference signal acquired in a phantom and potential coil‐loading differences are corrected using a synthetic reference signal. The aim of this study, conducted with a transceiver quadrature head coil, was to increase the accuracy of the ERETIC method by correcting the influence of spatial B1 inhomogeneities and to simplify the quantification with ERETIC by incorporating an automatic phase correction for the ERETIC signal. Transmit field ( B1+ ) differences are minimized with a volume‐selective power optimization, whereas reception sensitivity changes are corrected using contrast‐minimized images of the brain and by adapting the voxel location in the phantom measurement closely to the position measured in vivo. By applying the proposed B1 correction scheme, the mean metabolite concentrations determined with ERETIC in 21 healthy subjects at three different positions agree with concentrations derived with the tissue water signal as reference. In addition, brain water concentrations determined with ERETIC were in agreement with estimations derived using tissue segmentation and literature values for relative water densities. Based on the results, the ERETIC method presented here is a valid tool to derive in vivo metabolite concentration, with potential advantages compared with internal water referencing in diseased tissue.

Neurochemical profile of the human cervical spinal cord determined by MRS

MRS enables insight into the chemical composition of central nervous system tissue. However, technical challenges degrade the data quality when applied to the human spinal cord. Therefore, to date detection of only the most prominent metabolite resonances has been reported in the healthy human spinal cord. The aim of this investigation is to provide an extended metabolic profile including neurotransmitters and antioxidants in addition to metabolites involved in the energy and membrane metabolism of the human cervical spinal cord in vivo.

Quantitative magnetic resonance spectroscopy at 3T based on the principle of reciprocity

Quantification of magnetic resonance spectroscopy signals using the phantom replacement method requires an adequate correction of differences between the acquisition of the reference signal in the phantom and the measurement in vivo. Applying the principle of reciprocity, sensitivity differences can be corrected at low field strength by measuring the RF transmitter gain needed to obtain a certain flip angle in the measured volume. However, at higher field strength the transmit sensitivity may vary from the reception sensitivity, which leads to wrongly estimated concentrations. To address this issue, a quantification approach based on the principle of reciprocity for use at 3T is proposed and validated thoroughly. In this approach, the RF transmitter gain is determined automatically using a volume‐selective power optimization and complemented with information from relative reception sensitivity maps derived from contrast‐minimized images to correct differences in transmission and reception sensitivity. In this way, a reliable measure of the local sensitivity was obtained. The proposed method is used to derive in vivo concentrations of brain metabolites and tissue water in two studies with different coil sets in a total of 40 healthy volunteers. Resulting molar concentrations are compared with results using internal water referencing (IWR) and Electric REference To access In vivo Concentrations (ERETIC). With the proposed method, changes in coil loading and regional sensitivity due to B1 inhomogeneities are successfully corrected, as demonstrated in phantom and in vivo measurements. For the tissue water content, coefficients of variation between 2% and 3.5% were obtained (0.6–1.4% in a single subject). The coefficients of variation of the three major metabolites ranged from 3.4–14.5%. In general, the derived concentrations agree well with values estimated with IWR. Hence, the presented method is a valuable alternative for IWR, without the need for additional hardware such as ERETIC and with potential advantages in diseased tissue.

Detection of elevated ketone bodies by postmortem 1H-MRS in a case of fetal ketoacidosis

We report a fetal loss following maternal ketoacidosis in a case of cryptic pregnancy. Biochemical analysis of peripheral blood revealed highly elevated levels of beta-hydroxybutyrate (BHB) in the mother (9.2 mmol/l) and the fetus (4.2 mmol/l). Fetal ketoacidosis with hypoxic-ischemic brain damage was determined to be the cause of death. 1H-MRS of the right cerebral hemisphere presented with distinctive resonances of BHB and acetone. Acetoacetate and glucose were not detected. Due to reported chronic abuse of ethanol and a period of fasting, alcoholic ketoacidosis was concluded to be the cause of the metabolic disorder. 1H-MRS is a viable examination for the postmortem detection of ketone bodies and may be a key supplement to noninvasive fetal autopsy for the diagnosis of ketoacidosis.