Effects of contrast agents on relaxation properties of ³¹P metabolites

Phosphorous MR spectroscopy (³¹P-MRS) forms a powerful, non-invasive research tool to quantify the energetics of the heart in diverse patient populations. ³¹P-MRS is frequently applied alongside other radiological examinations, many of which use various contrast agents that shorten relaxation times of water in conventional proton MR, for a better characterisation of cardiac function, or following prior computed tomography (CT). It is, however, unknown whether these agents confound ³¹P-MRS signals, for example, 2,3-diphosphoglycerate (2,3-DPG).

In this work, we quantitatively assess the impact of non-ionic, low osmolar iodinated CT contrast agent (iopamidol/Niopam), gadolinium chelates (linear gadopentetic acid dimeglumine/Magnevist and macrocyclic gadoterate meglumine/Dotarem) and superparamagnetic iron oxide nanoparticles (ferumoxytol/Feraheme) on the nuclear T₁ and T₂ of ³¹P metabolites (ie, 2,3-DPG), and ¹H in water in live human blood and saline phantoms at 11.7 T.

Addition of all contrast agents led to significant shortening of all relaxation times in both ¹H and ³¹P saline phantoms. On the contrary, the T₁ relaxation time of 2,3-DPG in blood was significantly shortened only by Magnevist (P = .03). Similarly, the only contrast agent that influenced the T₂ relaxation times of 2,3-DPG in blood samples was ferumoxytol (P = .02).

Our results show that, unlike conventional proton MR, phosphorus MRS is unconfounded in patients who have had prior CT with contrast, not all gadolinium-based contrast agents influence ³¹P-MRS data in vivo, and that ferumoxytol is a promising contrast agent for the reduction in ³¹P-MRS blood-pool signal.