CEST MRI methods for imaging glutaminolysis in cancer
CEST imaging technique and MR scanning are used as an MRI method for measuring glutaminase mediated tumors. The method takes advantage of the fact that glutamine does not exhibit a significant Chemical Exchange Saturation Transfer (CEST) effect while glutamate does. In accordance with this method, one first obtains a glutamate CEST MRI map of the area of a tumor. L-glutamine (nontoxic up to several millimolar level) or glutaminase blocker is then injected and a post injection Glutamate CEST map is obtained. The difference in the spatial maps indicates the level of expression of glutaminase in the tumor.
1. A method of obtaining the level of expression of glutaminase in a tumor using MR imaging, comprising:
applying to a suspected tumor a Chemical Exchange Saturation Transfer (CEST) saturation pulse train at a range of frequency offsets around a frequency of exchangeable protons of glutamate as well as the same frequency offsets on the opposite of the water resonance;
MR imaging a slice of the body containing the suspected tumor to which the CEST saturation pulse has been applied to obtain a first glutamate CEST MRI map of the area of the tumor;
injecting L-glutamine or a glutaminase blocker into the tumor;
after injection of the L-glutamine or glutaminase blocker into the tumor, MR imaging a slice of the body containing the suspected tumor to which the CEST saturation pulse has been applied to obtain a second glutamate CEST MRI map of the area of the tumor;
determining a CEST contrast image by taking a ratio of a difference image obtained by subtraction of saturation images obtained during said MR imaging steps with saturation applied at both positive and negative frequencies with respect to water resonance and an image with no saturation; and
displaying the CEST contrast image as an indication of the level of expression of glutaminase in the tumor.
2. The method of claim 1 , further comprising adjusting an amplitude and duration of the CEST saturation pulse train based on the proton exchange rate of glutamate.
3. The method of claim 1 , wherein the CEST saturation pulse train comprises a variable number of pulses with variable shapes including rectangle and Hanning windowed rectangle, variable amplitudes, variable durations, and variable delays.
4. The method of claim 1 , further comprising B 0 and B 1 correcting the saturation images before subtracting said saturation images.