MRIsignaler

MRIsignaler refers to the electromagnetic signals generated by hydrogen nuclei in tissues during magnetic resonance imaging (MRI). These signals are detected by receiver coils and used to form images. They reflect underlying tissue properties, including proton density and relaxation times, and are influenced by sequence parameters and hardware.

In a strong static magnetic field, protons align along the field. A radiofrequency pulse tips the net magnetization into the transverse plane. When the pulse ends, transverse magnetization decays as spins dephase (T2) and realign along the longitudinal axis (T1 recovery). The decay and recovery emit the MR signal, which is then sampled over time.

The detected MR signal is spatially encoded by gradient fields. The data are organized in k-space and transformed to produce an image. Signal strength and contrast depend on tissue proton density and relaxation times; selecting specific pulse sequences (T1-weighted, T2-weighted, proton density-weighted, diffusion, perfusion) highlights different properties. Contrast agents can further alter T1 or T2 to improve visibility.

Signal quality is described by signal-to-noise ratio and is affected by coil design, field strength, patient motion, and magnetic field inhomogeneities, which can introduce artifacts such as ghosts, susceptibility effects, and geometric distortion (notably in diffusion- or functional MRI techniques).

MRIsignaler encompasses both routine diagnostic imaging and research applications, including functional MRI where changes in blood oxygenation level-dependent signals indicate neuronal activity. The technique uses no ionizing radiation, but safety considerations include implant compatibility and potential heating with strong fields.