Perfusion MRI using endogenous deoxyhemoglobin as a contrast agent: Preliminary data

Purpose: To demonstrate the feasibility of mapping cerebral perfusion metrics with BOLD MRI during modulation of pulmonary venous oxygen saturation. Methods: A gas blender with a sequential gas delivery breathing circuit was used to implement rapid isocapnic changes in the partial pressure of oxygen of the arterial blood. Partial pressure of oxygen was initially lowered to a baseline of 40 mmHg. It was then rapidly raised to 95 mmHg for 20 s before rapidly returning to baseline. The induced cerebral changes in deoxyhemoglobin concentration were tracked over time using BOLD MRI in 6 healthy subjects and 1 patient with cerebral steno-occlusive disease. BOLD signal change, contrast-to-noise ratio, and time delay metrics were calculated. Perfusion metrics such as mean transit time, relative cerebral blood volume, and relative cerebral blood flow were calculated using a parametrized method with a mono-exponential residue function. An arterial input function from within the middle cerebral artery was used to scale relative cerebral blood volume and calculate absolute cerebral blood volume and cerebral blood flow. Results: In normal subjects, average gray and white matter were: BOLD change = 6.3 +/- 1.2% and 2.5 +/- 0.6%, contrast-to-noise ratio = 4.3 +/- 1.3 and 2.6 +/- 0.7, time delay = 2.3 +/- 0.6 s and 3.6 +/- 0.7 s, mean transit time = 3.9 +/- 0.6 s and 5.5 +/- 0.6 s, relative cerebral blood volume = 3.7 +/- 0.9 and 1.6 +/- 0.4, relative cerebral blood flow = 70.1 +/- 8.3 and 20.6 +/- 4.0, cerebral blood flow volume = 4.1 +/- 0.9 mL/100 g and 1.8 +/- 0.5 mL/100 g, and cerebral blood flow = 97.2 +/- 18.7 mL/100 g/min and 28.7 +/- 5.9 mL/100 g/min. Conclusion: This study demonstrates that induced abrupt changes in deoxyhemoglobin can function as a noninvasive vascular contrast agent that may be used for cerebral perfusion imaging.