Which two of the following reduce the background noise in magneto- medicine?

Orienting the heart parallel to the earth’s field (parallometer)
Taking the difference of two nearby sensor measurements (gradiometer)
Orienting the heart perpendicular to the earth’s field (orthogometer)
Using physical means to shield environmental fields

The answer is b.) and d.)

Explanation:

The options to reduce the background noise in magneto-medicine are given as follows:

a.) Orienting the heart parallel to the Earth's field

   - This will have no significant effect on the measurements.

b.) Taking the difference of two nearby sensor measurements (gradiometer).

    -This answer is TRUE.

c.) Placing the heart in a perpendicular fashion to the Earth's magnetic field.

   _ This answer also will not have any significant effect on measurements.

d.) Using physical means to shield environmental fields.

   - This answer is TRUE.

grav forces affect all objects magnetic forces affect magnetic objects and electric currents