IC-MONA: Micro NMR sensor to detectneuronal activity

DFG Project

Proposed architecture of the TX/RX CMOS ASICs for MR signal detection and excitation.
The final functioning micro coil mounted on a PCB holder.

The main goal of the proposed project is the detection of neuronal activity-related changes of proton magnetization at an exceptionally high temporal resolution and sensitivity within small volumes of several nanoliters accompanied by simultaneous recording of electrical activity. In addition, we will use the intrinsic volume selection of our miniaturized detectors to assess local changes of neurotransmitters such as Glutamate/Glutamine/ GABA using proton spectroscopy, as well as energy metabolism via 31P spectroscopy both with high spatial resolution. To achieve these goals, we will develop a microsystem consisting of a miniaturized MR coil, microelectrodes for neural recording and a custom designed ASIC mounted on a common needle-shaped substrate. Here, in order to minimize the risk of tissue damage during probe insertion, the proposed multimodal probe will possess a needle-shape with shaft widths between 50 and 300 μm and shaft thicknesses below 100 μm. The ASICs will be designed in two different flavors: The first type of ASICs (RX ASICs) will contain all electronics required for the analog signal conditioning of both the recorded MR and electrical signals in order to provide robust signals at the ASIC output which can directly be digitized using a commercial analog-to-digital converter (ADC). The second type of ASICS (TX/RX ASICs) will additionally contain a transmit unit which will allow for a local excitation of the spin ensemble using the MR microcoil on the needle shaped probe head, operating the MR coil in transmit- receive mode. This local excitation not only mitigates all problems associated with RF current induced tissue heating but also reduces the risk of picking up parasitic MR signals in the local connections between MR coil and ASIC because it allows for an excitation of a spatially precisely defined area on top of the microcoil where the B1 field is strong enough to produce significant flip angles.

In addition to the combined MR/EP probe head, we will also implement the required electronic interface between a conventional MR scanner unit and the probe head. This interface will perform both the analog-to-digital conversion and storage of the acquired NMR and electrophysiological data. For the TX/RX ASICs we will additionally develop a software interface which will also provide the possibility to program the ASIC with custom pulse sequences. .

Overall, the envisioned system will allow us to capture localized activity within single layers and preferably within regions of different cellular components (dendrites, bodies, etc.). Together with electrical recording, direct study of neurovascular coupling can be performed at high temporal and spatial resolution to estimate locally dependent hemodynamic response functions. In addition, the envisioned miniaturized multimodal recording system will allow assessing neurovascular coupling on an exceptionally fine time scale enabling to resolve correlations between electrical signals and proton magnetization changes far below the commonly assumed time lag of several seconds (fast coupling). Pproposed architecture of the TX/RX CMOS ASICs for MR signal detection and excitation.

DFG Project SCHE 658/7
IC-MONA: Micro NMR sensor to detect neuronal activity
PI: K. Scheffler, J. Anders
Support total: EUR 501.430 (own support EUR 223.200)

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