The change of longitudinal relaxation rate in oxygen enhanced pulmonary MRI depends on age and BMI but not diffusing capacity of carbon monoxide in healthy never-smokers

Abstract

ObjectiveOxygen enhanced pulmonary MRI is a promising modality for functional lung studies and has been applied to a wide range of pulmonary conditions. The purpose of this study was to characterize the oxygen enhancement effect in the lungs of healthy, never-smokers, in light of a previously established relationship between oxygen enhancement and diffusing capacity of carbon monoxide in the lung (DL,CO) in patients with lung disease.MethodsIn 30 healthy never-smoking volunteers, an inversion recovery with gradient echo read-out (Snapshot-FLASH) was used to quantify the difference in longitudinal relaxation rate, while breathing air and 100% oxygen, ΔR1, at 1.5 Tesla. Measurements were performed under multiple tidal inspiration breath-holds.ResultsIn single parameter linear models, ΔR1 exhibit a significant correlation with age (p = 0.003) and BMI (p = 0.0004), but not DL,CO (p = 0.33). Stepwise linear regression of ΔR1 yields an optimized model including an age-BMI interaction term.ConclusionIn this healthy, never-smoking cohort, age and BMI are both predictors of the change in MRI longitudinal relaxation rate when breathing oxygen. However, DL,CO does not show a significant correlation with the oxygen enhancement. This is possibly because oxygen transfer in the lung is not diffusion limited at rest in healthy individuals. This work stresses the importance of using a physiological model to understand results from oxygen enhanced MRI.

Modeling the Effect of Hyperoxia on the Spin–Lattice Relaxation Rate R1 of Tissues

“…It is interesting that hematocrit differences in the male and female populations did have a slight effect on ΔR1 when the voxel contained larger blood volumes. In fact, this predicted difference has been empirically observed in lung tissue — where blood volume is approximately 33%–36% 42 — Kindvall et al 12 reported that age and sex were all predictors of ΔR1 in lung tissue, likely due to the hematocrit differences.…”

“…For example, measurements of R1 have been used to infer oxygen levels in vitreous fluid as a noninvasive alternative to the highly invasive oxygen electrodes used to measure retinal hypoxia, 1–3 bladder urine, 4 and urine in the renal pelvis to create a non‐invasive detection of renal dysfunction, 5 and cerebrospinal fluid 4,6 . Additionally, measuring changes in R1 following the inspiration of increased fractions of oxygen is the basis for oxygen‐enhanced MRI techniques, 7–9 which are used to study a range of conditions from tumor hypoxia 8,10,11 to lung disease 12,13 …”

“…4,6 Additionally, measuring changes in R1 following the inspiration of increased fractions of oxygen is the basis for oxygen-enhanced MRI techniques, [7][8][9] which are used to study a range of conditions from tumor hypoxia 8,10,11 to lung disease. 12,13 The linear relationship between the partial pressure of oxygen (PO 2 ) in a material and the resulting longitudinal relaxation rate (R1) has been measured in phantoms [2][3][4]6,14 and bodily fluids such as vitreous fluid. 2 The relationship between R1 and PO 2 has been modeled as for a paramagnetic contrast agent, R1 Ox = R1 0 + r1 Ox *C, where R1 Ox is the relaxation rate in the solution with oxygen added, R1 0 is the relaxation rate in the solution without oxygen, C is the concentration of oxygen added, and r1 Ox is the relaxivity of oxygen in that solution, which is dependent on the magnetic field and temperature.…”

Oxygen-enhanced MRI and radiotherapy in patients with oropharyngeal squamous cell carcinoma

“…Over the years, OE-MRI studies have used a variety of methods to detect the change in R1 – some have used semi-quantitative signal intensity changes in T1-weighted imaging [12] , [19] , [35] , [51] , [52] , and some have used quantitative T1 mapping methods such as inversion recovery [13] , [22] , [25] , [53] , [54] , [55] , saturation recovery [56] , VFA [11] , [39] , [50] , [57] , [17] , [18] , [19] , or Look-Locker variants such as MOLLI [28] , [34] , [38] , [58] , [59] . There are tradeoffs between T1 estimation accuracy and acquisition time between each of these methods, and some are known to overestimate (VFA) or underestimate (Look-Locker variants) the true T1 of the material [60] , with inversion recovery being the ‘gold-standard’ technique.…”

Review of oxygen‐enhanced lung mri: Pulse sequences for image acquisition and T1 measurement

“…Previous studies have also illustrated that the T 1 reduction is proportional to the partial pressure of oxygen in lung blood 19,31,32 . Since the partial pressure of oxygen in the pulmonary veins (more than 500 mmHg) is much higher than that in arteries (15 mmHg), 33 the venous compartment will contribute more than the arteries during oxygen breathing 34–36 . Therefore, the T 1 reduction is a combination result of blood, blood vessels and alveolar cells, especially venous blood.…”