MRI parts and technology are teeming with jargon. From coils to compressors, “tesla” is another word the average MRI technician needs to define. No, it doesn’t pertain to the renowned electric vehicle.
Instead, tesla describes the magnitude (B) of an MRI field at a given point. If the area is perfectly uniform, B remains the same at all points. In this guide, we’ll take you through the basics of tesla and its implications for high-quality MRI equipment.
A magnetic field is formally defined as “an array of vectors whose magnitude B and direction at each point in space define how the field will act on a charge moving at that location.”
Imagine a hypothetical wire across the bore of an MRI scanner. As current travels along the wire, a Lorentz force deflects it upward. The force (F) is proportional to the current (i), length of the wire (l), and strength of the magnetic field (B). As such, you can observe the formula:
F = (i l) B
Therefore, tesla (T) represents the dimensional units for B, which are newtons per ampere-meter. For example, a wire pumping a current of 1-ampere perpendicular to a 3.0-tesla field boasts a deflecting force of 3.0 N along each meter of length. In vector form, the formula is:
F = I x B, where each are vectors defined by the cross product and right-hand rule. I represents a current vector whose B and direction are the wire’s length multiplied by the conventional current charge flow (i).
Tesla Concerning the MRI Magnet
Most technicians will refer to a magnetic resonance (MR) scanner according to their magnetic field strength. As such, scanners are typically labeled 1.5T or 3.0T scanners.
Here, tesla defines the magnetic flux density, which exists on the metric system. One tesla is equivalent to one weber per square meter and 10,000 gausses. Higher tesla scanners possess a stronger magnet of up to 7.0T.
Why Does the MRI Magnet Matter?
An MRI machine is only as good as its magnet. Observe it in these terms. The Earth produces a magnetic field of 0.5 gausses. A 1.5T MRI scanner produces 15,000 gausses, nearly 30,000 stronger than the Earth’s magnetic pull.
This strength allows the scanner to align hydrogen nuclei to produce images during an MRI exam. The power of a magnet directly impacts the machine’s ability to receive signals from the body.
1.5T vs. 3.0T Scanners
A 1.5T MRI scanner is the standard imaging method for most exams. In some cases, a stronger magnet of 3.0T is necessary for examinations concerning the prostate, MR spectroscopy, functional MRI, and arterial spin labeling.
Between the two, a 1.5T scanner can improve the quality of images during longer sequences, whereas a 3.0T scanner provides better clarity and detail. A 3.0T scanner can cater to more patients in the same amount of time a 1.5T scanner can process one.
Does Stronger Mean Better?
When it comes to MR, a higher signal-to-noise ratio (SNR) will produce superior image quality. This is because the signal being read and transmitted to a computer reduces obstructions from noise and vibrations. Thus, stronger magnets perform better after spatial resolution correction.
Stronger magnets also increase T1 dispersion, which probes the behavior of macromolecules in tissue. In contrast to gadolinium-based contrast mediums, T1 dispersion is a form of magnetization transfer contrast (MTC).
An MR angiography (MRA) measures this amount to study blood vessels in a specific area of the body. This procedure can detect abnormalities and detect blood disorders.
The final aspect of MRI imaging is MR spectroscopy (MRS), which measures the difference in a nucleus’ resonance frequency and the shift in this frequency by magnetic fields. The MRS analyzes and diagnoses abnormalities in the brain and central nervous system. Stronger magnetic fields allow for a more accurate study through an increased chemical shift.
Whether 1.5T, 3.0T, or 7.0T, each MR scanner has its place in the MRI industry. As a rule of thumb, utilize 1.5T systems for routine exams, 3.0T systems for more detailed examinations, and 7.0T systems for increased T1 dispersion and research purposes.
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