Influence of oxygen flow rate on signal and T₁ changes in oxygen‐enhanced ventilation imaging

Abstract

Purpose: To investigate the optimal oxygen flow rate for oxygen-enhanced MR ventilation imaging. Materials and Methods:Using a cardiac-triggered nonselective inversion recovery (IR) half Fourier single-shot fast spin echo sequence, series of images were acquired with the subject alternately inhaling room air and 100% oxygen. Oxygen flow rates of 5 L/min, 10 L/min, 15 L/min, 20 L/min, and 25 L/min were studied, and signal intensity from the oxygen-enhanced ventilation images and T 1 of the lung were measured. OXYGEN-ENHANCED MAGNETIC RESONANCE IMAG-ING has been used to assess regional ventilation of the lung in patients with pulmonary diseases and in animal models (1-4). Although oxygen is weakly paramagnetic, its overall effect on the lung is considerable given the large surface area of the lung and the large difference in partial pressures between room air and 100% oxygen. ResultsRelative to breathing room air, inhaling 100% oxygen increases concentration of dissolved oxygen in blood and lung tissue as more oxygen diffuses across the lung parenchyma and dissolves into blood and lung tissues. Consequently, increased concentration of dissolved oxygen in the lung will shorten its longitudinal relaxation time (T 1 ), enabling the detection of signal change if T 1 -weighted sequences such as inversion recovery (IR) or multiple IR are used for image acquisition (1-8). Generally, the procedure of the oxygen-enhanced ventilation imaging technique involves the acquisition of series of images with the subject alternately inhaling room air and 100% oxygen. The difference between the average images of the two states yields the oxygenenhanced ventilation image.To date, oxygen-enhanced ventilation imaging has been performed using different flow rates (1-7,9,10), while no study thus far has been conducted to determine the influence of oxygen flow rate on the signal and T 1 changes in the lung. Logically, if more oxygen dissolves in blood plasma in the lung, a larger detected signal change will result. However, the solubility of oxygen in blood plasma is poor, and therefore a low saturation point would be quickly established. Thus, there should exist an optimal point for changes in signal intensity and T 1 of the lung. The purpose of this study was to investigate the effect of oxygen flow rate for ventilation imaging of the lung with inhalation of 100% oxygen. More specifically, we sought to determine the oxygen flow rate at which optimal changes in signal intensity and T 1 of the lung occur. MATERIALS AND METHODSAll imaging experiments were performed on a CV/i 1.5 T system (GE Medical Systems, Milwaukee, WI) equipped with 40 mT/m gradients and a slew rate of 150 T/m/second. A four-element, receiver phased-array coil was used. Six healthy human volunteers (three males and three females, 25-48 years old, average age 33.7 Ϯ 6.5 years) were imaged. Written informed consent was obtained from each volunteer before experimentation.A series of 60 images at TI of 1200 msec were acquired at each flow rate while the subjects alternately...

Imaging lung function using rapid dynamic acquisition of T 1-maps during oxygen enhancement

“…A new approach for a rapid dynamic acquisition of T 1 -maps was introduced. The T 1 values in the human lung range from 800 ms to 1400 ms [8,19,23,24]. The results of the measurements on a phantom, which consisted of tubes with T 1 in the range of 700-1450 ms, clearly illustrated its feasibility for lung T 1 -mapping.…”

“…For administration of breathing gas we constructed a breathing system that was non-rebreathing and allowed for fast switching between air and pure oxygen. The flow rate was 15-25 l/min, as was found to be optimal in [19]. The volunteers breathed through the same kind of mouthpiece as employed in the clinical lung function laboratory.…”

Functional MRI of the Lung

“…1b). The optimum dosage for 100% O 2 was shown to be 15 L/min [26]. Administration of 100% oxygen with this dosage has been shown to produce oxygen concentrations in the lung of 60-80% [27].…”

Aerosols and gaseous contrast agents for magnetic resonance imaging of the lung

“…The optimum dosage for 100% O 2 was shown to be 15 L/min (72). Administration of 100% oxygen with this dosage has been shown to produce oxygen concentrations in the lung of 60-80% (71).…”