Improving deuterium metabolic imaging (DMI) signal-to-noise ratio by spectroscopic multi-echo bSSFP: A pancreatic cancer investigation

Purpose Deuterium metabolic imaging (DMI) maps the uptake of deuterated precursors and their conversion into lactate and other markers of tumor metabolism. Even after leveraging H-2's short T(1)s, DMI's signal-to-noise ratio (SNR) is limited. We hypothesize that a multi-echo balanced steady-state free precession (ME-bSSFP) approach would increase SNR compared to chemical shift imaging (CSI), while achieving spectral isolation of the metabolic precursors and products. Methods Suitably tuned H-2 ME-bSSFP (five echo times [TEs], Delta TE = 2.2 ms, repetition time [TR]/flip-angle = 12 ms/60 degrees) was implemented at 15.2T and compared to CSI (TR/flip-angle = 95 ms/90 degrees) regarding SNR and spectral isolation, in simulations, in deuterated phantoms and for the in vivo diagnosis of a mouse tumor model of pancreatic adenocarcinoma (N = 10). Results Simulations predicted an SNR increase vs. CSI of 3-5, and that the peaks of H-2-water, H-2(6,6')-glucose, and H-2(3,3')-lactate can be well isolated by ME-bSSFP; phantoms confirmed this. In vivo, at equal spatial resolution (1.25 x 1.25 mm(2)) and scan time (10 min), H-2(6,6')-glucose's and H-2(3,3')-lactate's SNR were indeed higher for bSSFP than for CSI, three-fold for glucose (57 +/- 30 vs. 19 +/- 11, P < .001), doubled for water (13 +/- 5 vs. 7 +/- 3, P = .005). The time courses and overall localization of all metabolites agreed well, comparing CSI against ME-bSSFP. However, a clearer localization of glucose in kidneys and bladder, the detection of glucose-avid rims in certain tumors, and a heterogeneous pattern of intra-tumor lactate production could only be observed using ME-bSSFP's higher resolution. Conclusions ME-bSSFP provides greater SNR per unit time than CSI, providing for higher spatial resolution mapping of glucose uptake and lactate production in tumors.

Automated summary

Deuterium metabolic imaging (DMI) maps the uptake and conversion of deuterated precursors in tumors. Through multi-echo balanced steady-state free precession (ME-bSSFP) approach, increased signal-to-noise ratio (SNR) and spectral isolation of metabolic precursors and products were achieved. Results showed ME-bSSFP provides higher SNR and spatial resolution for mapping glucose uptake and lactate production in tumors compared to chemical shift imaging (CSI).