Figure 4.

Demonstrates the use of Eq. 2 to generate contrast based on the magnitude of dispersion and chemical exchange rate for phantoms of the X-ray contrast agent Iohexol (32 mM), BSA (10 % wt/wt), and a combined IO + BSA mixture.

4.a. Low power (SLA = 250 Hz), short duration (SLT = 20 msec) image of all three phantoms: Top Left = IO alone, Top Right = BSA alone, Bottom = Both.

4.b. An image representing the numerator of Eq. 2, with the subtraction of a low power (250 Hz) image from a higher power image (2800 kHz) at 176 msec. The high power value was chosen to enhance sensitivity to the exchange rate of the IO + BSA phantom. Note the large contrast difference between the BSA phantoms with and without the presence of IO. The spin-locking pulse acts as an exchange-rate filter, enhancing contrast from the phantoms with exchange rates slower than the high-power locking field and with large dispersions.

4.c. A normalized percent contrast enhancement image from Eq. 2. Phantoms with IO show a large contrast enhancement. Note that the BSA+IO phantom shows an enhancement of 70–80% due to the presence of IO, while BSA alone has almost no enhancement.