Observation of Human Cardiac Bloodflow by Non-Invasive Measurement of Magnetic Susceptibility Changes

A susceptibility cryostat has been built to measure the bloodflow in the in situ human heart. A superconducting magnet is used to generate a constant magnetic field encompassing the heart. Changes in intracardiac blood volume induce small proportional changes in the external magnetic field because the magnetic susceptibility of blood differs from that of the surrounding tissue. In a simple model, 140ml of blood moving 5cm in a 100 gauss field will produce a field change of ${\text{5×10}}^{\text{−5}}\hspace{0.17em}\mathrm{gauss}$ . These changes are detected with a SQUID gradient magnetometer which is rigidly attached to the magnet. The spatial and temporal dependence of the blood flow signal is being studied in an attempt to develop new non‐invasive techniques for evaluating cardiac function. To facilitate these measurements, a 25 ft. deep, 6 ft. diameter, two layer Molypermalloy magnetic shield has been constructed with an internal D.C. field of ${\text{5×10}}^{\text{−4}}\hspace{0.17em}\mathrm{gauss}$ and typical gradients of 10⁻⁶ g/cm. In addition, the data will be computer processed for greater noise rejection without a loss in bandwidth.