The need for liquid Helium in conventional MEG systems has some disadvantages. Which of the following statements is NOT one of them?

Question

BlackTom AI · Accepted Answer

Because conventional MEG sensors (SQUIDs) must be kept at cryogenic temperatures with liquid helium, several practical constraints follow — but a magnetically shielded room is not one of them caused by the cryogenics.

1) Relevant knowledge points and concepts
- SQUID-based MEG uses superconducting sensors cooled with liquid helium inside a rigid cryostat (Dewar).  
- The Dewar imposes a fixed geometry and a thermal/vacuum gap between the cold sensors and the scalp.  
- MEG measures extremely small magnetic fields, so external magnetic shielding is required for sensitivity, but that requirement is independent of the cooling method.

2) Step-by-step reasoning
- Liquid helium cooling requires a Dewar, which physically separates the sensors from the head. That increases sensor-to-scalp distance, reducing signal amplitude (fields fall off with distance).  
- The Dewar is usually a fixed helmet shape; you cannot custom-fit sensor arrays to different head sizes or shapes because the sensors are embedded in the cold, rigid cryostat.  
- Because sensors are fixed relative to the Dewar, subjects must keep their head still inside the helmet — free movement is restricted.  
- A magnetically shielded room is used to block external magnetic noise so tiny brain fields can be detected; this is necessary regardless of whether sensors use liquid helium (even cryogen-free MEG or OPMs often benefit from shielding).

3) Calculations
- No numeric calculation is needed; the argument depends on physical geometry and instrumentation constraints.

4) Why the correct answer is correct
- "The need for a magnetically shielded room" is NOT a disadvantage that specifically arises from using liquid helium. It is a general requirement of MEG sensitivity, not a consequence of the cryogenic cooling.

5) Why other options are incorrect
- "Sensors cannot be placed too close to the head" — true: the Dewar gap forces sensor distance and signal loss.  
- "Sensor arrays are not custom-built..." — true: the fixed cryostat prevents custom-fit arrays.  
- "Participants cannot move freely..." — true: the helmet/Dewar requires the head to remain in a fixed position.

6) Conclusion
The statement that is NOT a disadvantage caused by the need for liquid helium is "The need for a magnetically shielded room," which matches the provided correct answer.

The need for liquid Helium in conventional MEG systems has some disadvantages. Which of the following statements is NOT one of them?单项选择题

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