Induction of Gradual Changes in Blood Oxygen Levels in Post Lumpectomy Breast Tissue With Breath Holding: Results of a Pilot Study

Abstract

Our pilot study investigates whether changes in breast tissue oxygenation, as measured by BOLD MRI contrast, occur with breath holding schedules typically utilized during adjuvant left breast radiation therapy. Ten women status post lumpectomy for breast cancer and undergoing treatment planning for whole breast radiation therapy were enrolled. Each subject underwent an imaging session on a 1.5T GE MRI, immobilized in the prone position on a custom board with a 4 channel breast coil. BOLD contrast MRI imaging was performed using two MRI sequences: T2* based Gradient Echo EPI (TR/TE = 500/41ms, flip angle = 60°) and T2 based Single Shot Fast Spin Echo (SSFSE) (TR/TE = 3000/60ms). For each imaging sequence 1-3 planes of the breast were imaged continuously. After a 1 minute background measurement the subject was asked to hold their breath at inspiration for 20-40 seconds, with 3-5 breath holds total per imaging sequence. We quantified changes in oxygenation as the correlation between the breath holding signal and per-pixel intensity changes from each MRI image sequence. We also investigated the rate of oxygenation response to breath holding using various hemodynamic functions convolved with the breath hold schedule. Statistical significance for BOLD contrast was set at p<0.001. On T2* sequences, all subjects had mixed BOLD contrast signal with areas of increasing and decreasing oxygenation occurring in localized adjacent areas. On T2 sequences, three subjects had consistent oxygen decreases throughout the breast and three subjects had consistent oxygen increases throughout the breast. Compared to a fast hemodynamic function (5s), a slow function (180s) showed increased BOLD contrast within the breast; suggesting that breast oxygenation changes are generally slow hemodynamic effects and are additive over multiple breath holds. We observed correlation between breath holding and blood oxygenation as quantified by BOLD contrast MRI for 6/10 whole breast radiation therapy candidates; however the pattern and magnitude varied considerably between subjects. Changes in breast oxygenation appear to occur slowly and are additive over multiple breath holds. Further study in a larger sample is needed to better understand the effect of breath hold technique on breast tissue oxygenation.