NYU Medical Center has a 7 tesla MR system. What is the flux density in gauss? 2) Using the following conversions, calculate the magnetic field strength (amps/meter) of a 0.35 T system. 1 gauss (magnetic flux density) is equivalent to 1 oersted (magnetic field strength) 1 oersted (Oe) = 79.58 A/m
The Correct Answer and Explanation is:
1) What is the flux density in gauss for a 7 Tesla MR system?
Conversion factor:
1 Tesla = 10,000 gauss
Calculation:7 Tesla×10,000 gaussTesla=70,000 gauss7 \, \text{Tesla} \times 10{,}000 \, \frac{\text{gauss}}{\text{Tesla}} = 70{,}000 \, \text{gauss}7Tesla×10,000Teslagauss=70,000gauss
Answer: The flux density is 70,000 gauss.
2) What is the magnetic field strength (in A/m) of a 0.35 Tesla system?
Step 1: Convert Tesla to gauss0.35 T×10,000 gaussT=3,500 gauss0.35 \, \text{T} \times 10{,}000 \, \frac{\text{gauss}}{\text{T}} = 3{,}500 \, \text{gauss}0.35T×10,000Tgauss=3,500gauss
Step 2: Use the fact that 1 gauss = 1 oersted3,500 gauss=3,500 oersted3{,}500 \, \text{gauss} = 3{,}500 \, \text{oersted}3,500gauss=3,500oersted
Step 3: Convert oersted to A/m3,500 Oe×79.58 A/mOe=278,530 A/m3{,}500 \, \text{Oe} \times 79.58 \, \frac{\text{A/m}}{\text{Oe}} = 278{,}530 \, \text{A/m}3,500Oe×79.58OeA/m=278,530A/m
Answer: The magnetic field strength is 278,530 A/m.
Explanation (Textbook-style):
Magnetic resonance imaging (MRI) systems are characterized by the strength of their magnetic field, typically measured in tesla (T), the SI unit for magnetic flux density (also known as magnetic induction, symbol B). One tesla is equivalent to 10,000 gauss, a unit historically used in the CGS system. For instance, NYU Medical Center’s 7 T MRI scanner generates a flux density of 70,000 gauss. This strong magnetic field allows for higher-resolution imaging by increasing signal-to-noise ratio and tissue contrast.
While B (flux density) is measured in tesla or gauss, the magnetic field strength H is a different quantity, representing the magnetizing force and measured in amperes per meter (A/m) in the SI system. In the CGS system, H is measured in oersted (Oe). For non-magnetic materials like human tissue, 1 gauss of magnetic flux density corresponds approximately to 1 oersted of field strength.
To convert H from oersted to A/m, the conversion factor is:1 Oe=79.58 A/m1 \, \text{Oe} = 79.58 \, \text{A/m}1Oe=79.58A/m
Thus, a 0.35 T (3,500 gauss) system has a magnetic field strength of approximately 278,530 A/m. Understanding these conversions is crucial in medical physics and MRI engineering, especially when interpreting system specifications or comparing technologies using different unit systems.
