Imaging Lung Cancer by Using Chemical Exchange Saturation Transfer MRI With Retrospective Respiration Gating.

Charles Hsu,Phillip Kuo,Kyle Jones,Edward Randtke,Mark Pagel,Carol Stuehm

doi:10.18383/j.tom.2017.00017

Abstract

Performing chemical exchange saturation transfer (CEST) magnetic resonance imaging (MRI) in lung tissue is difficult because of motion artifacts. We, therefore, developed a CEST MRI acquisition and analysis method that performs retrospective respiration gating. Our method used an acquisition scheme with a short 200-millisecond saturation pulse that can accommodate the timing of the breathing cycle, and with saturation applied at frequencies in 0.03-ppm intervals. The Fourier transform of each image was used to calculate the difference in phase angle between adjacent pixels in the longitudinal direction of the respiratory motion. Additional digital filtering techniques were used to evaluate the breathing cycle, which was used to construct CEST spectra from images during quiescent periods. Results from CEST MRI with and without respiration gating analysis were used to evaluate the asymmetry of the magnetization transfer ratio (MTRasym), a measure of CEST, for an egg white phantom that underwent cyclic motion, in the liver of healthy patients, as well as liver and tumor tissues of patients diagnosed with lung cancer. Retrospective respiration gating analysis produced more precise measurements in all cases with significant motion compared with nongated analysis methods. Finally, a preliminary clinical study with the same respiration-gated CEST MRI method showed a large increase in MTRasym after radiation therapy, a small increase or decrease in MTRasym after chemotherapy, and mixed results with combined chemoradiation therapy. Therefore, our retrospective respiration-gated method can improve CEST MRI evaluations of tumors and organs that are affected by respiratory motion.

Highlights

Lung cancer is the leading cause of cancer-related death in both men and women in the United States, accounting for 27% of cancer deaths in 2014 [1]
This lower contrast was expected, because interleaving a 196-millisecond delay with the saturation pulses to account for the Fast Imaging with Steady-state Precession (FISP) acquisition sequence lowered the duty cycle of the saturation during the entire chemical exchange saturation transfer (CEST) magnetic resonance imaging (MRI) protocol
Phantom Studies Our studies with phantoms undergoing motion showed that the iteratively pulsed CEST MRI acquisition with retrospective respiration gating analysis generated more precise MTRasym values compared with the standard CEST MRI acquisition method and

Summary

Introduction

Lung cancer is the leading cause of cancer-related death in both men and women in the United States, accounting for 27% of cancer deaths in 2014 [1]. Positron emission tomography (PET) with 18F-fluordeoxyglucose (FDG), diffusion-weighted magnetic resonance imaging (DW-MRI), perfusion MRI, and computed tomography (CT) have been used to noninvasively evaluate lung masses [2,3,4,5]. PET with FDG is a highly sensitive imaging technique, but FDG uptake is nonspecific to tumors, and areas of inflammation may be falsely identified as tumor tissue. Perfusion CT and MRI have been shown to distinguish malignant nodules from benign pulmonary nodules with greater specificity than assessments of FDG uptake. This result has been shown in only lesion sizes Ն16 mm, limiting its use to a fraction of the patient population. Additional techniques are required for evaluating lung tumors with medical imaging

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