The characteristic knocking and hammering sounds are caused by the so-called gradient coils inside the scanner. When electrical pulses are passed through these coils for the scan, extremely strong magnetic forces act upon them. This causes the components to oscillate mechanically and vibrate slightly within the housing. The result is that typical noise, which is somewhat reminiscent of a construction site or techno music. The intensity of this vibration varies depending on the type of tissue the machine is currently imaging.
An MRI exam almost never consists of just a single image; instead, it comprises several different sequences. Each sequence produces a different type of image—for instance, to highlight inflammation or visualize different tissue types. To gather the necessary information, the magnetic field of the gradient coils must be switched on and off at varying rhythms, intensities, and speeds. Consequently, a short, rapid thumping indicates a different sequence than a long, deep humming or beeping sound.
No; according to current scientific knowledge, an MRI scan is completely harmless to the human body. Unlike X-rays, the scanner does not use ionizing radiation but instead relies on a strong magnetic field and harmless radio waves. As a result, tissue is not damaged, nor is there any cumulative exposure that builds up over a lifetime.
The compact design is based on purely physical principles: to obtain razor-sharp images, the magnetic field generated inside the machine must be extremely uniform and strong. The tighter the tunnel’s construction, the more precisely and energy-efficiently this high-energy field can be established. The additional coils placed on areas such as the knee, shoulder, or abdomen before the scan function essentially like small receiving antennas. They capture the tiny signals emitted by your body within the magnetic field—right at the skin’s surface—and transmit them to the computer. If these coils were positioned too far from the body, image quality would deteriorate significantly, making it difficult to detect fine details such as tendon tears or minor inflammation. Ultimately, the confined space serves to ensure the most accurate diagnosis possible.
There are contraindications where an MRI cannot be performed at all, or only under specific precautionary measures. The most common reason is the presence of metallic or electronic objects in the body. Pacemakers, insulin pumps, cerebral aneurysm clips, or metal fragments in the eye can shift or heat up intensely due to the extremely strong magnetic field. Certain tattoos containing metallic pigments or older joint prostheses also require careful prior assessment. While modern implants are often „MRI-safe,“ their status must always be verified beforehand using the manufacturer’s documentation. Severe claustrophobia or pregnancy during the first trimester usually also rule out an MRI scan.
| Sequence | Meaning | Sequence Indication |
|---|---|---|
| Localizer/Scout | Three-dimensional / In three planes: sagittal, axial, coronal | Anatomical orientation and navigation aid for the precise planning of all subsequent measurement slices in all three spatial planes. |
| 3D MPRAGE | High-resolution imaging of brain anatomy and performance of volumetric measurements | |
| FLAIR | Fluid Attenuated Inversion Recovery-Sequence | Detection of tissue edema, inflammations (e.g., MS), and lesions. |
| GRE | Gradient Recalled Echo | Detection of blood breakdown products (microbleeds) and calcifications. |
| TSE | Turbo Spin Echo | Standard morphology for the assessment of the parenchyma, ventricles, and subarachnoid space. |
| DWI | Diffusion Weighted Imaging | Used to detect acute ischemic strokes. |
| DTI | Diffusion Tensor Imaging | Used for the detailed visualization and analysis of white matter and neuronal pathways (nerve fiber tracts) in the brain. |
| SMPM | Structural/Quantitative Multiparameter Mapping | Serve for quantitative tissue characterization. |
| SPACE | Sampling Perfection with Application optimized Contrasts | High-resolution imaging for the precise delineation of small cortical lesions or meningeal processes. |
| resolve | Readout Segmentation of Long Variable Echotrains | High-resolution diffusion imaging. |
| BOLD resting state | Blood Oxygen Level Dependent – fMRT | Functional MRI (fMRI) for measuring local brain activation during task performance. Assessment of resting-state networks in the brain without a specific task being performed by the subject. |
| asl pcasl | Arterial Spin Labeling Pseudo-Continuous Arterial Spin Labeling | Visualization of arterial blood flow without contrast agent. |
| BEAT | Cardiac Beat Sequence | ECG-synchronized cardiac sequence for capturing flow phenomena in the heart |
T1: It depicts adipose tissue as bright and fluids (such as cerebrospinal fluid) as dark, thereby providing the best anatomical detail contrast. It is preferred for the high-resolution assessment of brain structures and for volumetry.
T2: It displays free fluids and abnormal tissue changes as bright areas, making it extremely sensitive to edema, inflammation, or lesions. It forms the basis of standard morphological diagnostics for the rapid detection of pathological processes in the brain.