Differences in Hemodynamic Alteration between Atherosclerotic Occlusive Lesions and Moyamoya Disease: A Quantitative 15O-PET Study

To clarify the differences in hemodynamic status between atherosclerotic steno-occlusive lesions (SOL) and moyamoaya disease (MMD), hemodynamic parameters were compared using 15O-PET. Twenty-four patients with unilateral SOL (67 ± 11 y) and eighteen with MMD (33 ± 16 y) were assigned to this study. MMD patients were divided into twelve unilateral and six bilateral lesions. All patients underwent 15O-PET to measure cerebral blood flow (CBF), blood volume (CBV), oxygen extraction fraction (OEF), and metabolic rate (CMRO2). Acetazolamide was administered after the baseline scan and the second 15O-water PET was performed to evaluate cerebrovascular reactivity (CVR). For the CBF calculation in 15O-water PET, the three-weighted integral method was applied based on a one-tissue compartment model with pixel-by-pixel delay correction to measure precise CBF and arterial-to-capillary blood volume (V0). Baseline hemodynamic parameters showed significantly lower CBF, V0, and CMRO2, but greater CBV, OEF, and delay (p < 0.01) in the affected hemispheres than in the unaffected hemispheres. After ACZ administration, both hemispheres showed a significant increase in CBF (p < 0.0001), but not in V0. CVR differed significantly between the hemispheres. The arterial perfusion pressure of the functioning arterial part tended to be reduced after acetazolamide administration in patients with past neurologic events caused by hemodynamic impairment. MMD patients showed greater inactive vascular and venous volumes compared with common atherosclerotic SOL patients. The hemodynamic status of cerebral circulation may vary according to the chronic process of steno-occlusive change and the development of collateral circulation. In order to evaluate physiologic differences between the two diseases, 15O-PET with an acetazolamide challenge test is useful.

Using Hyperpolarized 129Xe Gas Exchange MRI to Model the Regional Airspace, Membrane and Capillary Contributions to Diffusing Capacity

Hyperpolarized 129Xe MRI has emerged as a novel means to evaluate pulmonary function via 3D mapping of ventilation, interstitial barrier uptake, and RBC transfer. However, the physiological interpretation of these measurements has yet to be firmly established. Here we propose a model that uses the three components of 129Xe gas exchange MRI to estimate accessible alveolar volume (VA), membrane conductance, and capillary blood volume contributions to DLCO 129Xe ventilated volume (VV) was related to VA by a scaling factor kV=1.47 with 95% confidence interval [1.42, 1.52], relative 129Xe barrier uptake (normalized by the healthy reference value) was used to estimate the membrane specific conductance coefficient kB=10.6 [8.6, 13.6] mL/min/mmHg/L, while normalized RBC transfer was used to calculate the capillary blood volume specific conductance coefficient kR=13.6 [11.4, 16.7] mL/min/mmHg/L. In this way, the barrier and RBC transfer per unit volume determined the transfer coefficient KCO, which was then multiplied by image-estimated VA to obtain DLCO. The model was built on a cohort of 41 healthy subjects and 101 patients with pulmonary disorders. The resulting 129Xe-derived DLCO correlated strongly (R2=0.75, p<0.001) with the measured values, a finding that was preserved within each individual disease cohort. The ability to use 129Xe MRI measures of ventilation, barrier uptake and RBC transfer to estimate each of the underlying constituents of DLCO both clarifies the interpretation of these images, while enabling its use to monitor these aspects of gas exchange independently and regionally.

Potential of Perfusion Magnetic Resonance Imaging to Predict Residual Renal Function after Radical Nephroureterectomy

Introduction: The diffusion-weighted imaging (DWI) technique with intravoxel incoherent motion model enables the estimation of capillary blood volume as a perfusion-related parameter- (PP-) value. Therefore, the PP-value of the kidney theoretically reflects renal capillary blood volume. We analyzed the usefulness of the PP-value in estimating postoperative renal function in upper-tract urothelial carcinoma (UTUC) patients. Methods: Forty-eight consecutive patients who underwent magnetic resonance imaging before radical nephroureterectomy from 2011 to 2018 were analyzed. A PP-map displaying PP-values on a pixel-by-pixel basis was created from DWI signals (b-values of 0, 500, and 1,000 s/mm2). Two readers independently analyzed the renal PP-value. DWI-based split renal function (SRF) of the intact kidney was calculated by splitting serum Cr-based preoperative estimated glomerular filtration rates (eGFRs). The predictive accuracy of the method was evaluated using renography as the reference standard. Results: Interobserver analysis revealed an excellent correlation value of 0.97. The SRF value showed a good linear correlation with the observed postoperative eGFR (r = 0.76, p < 0.001). The predictive accuracy of the DWI-based method was similar to that of the nuclear-based method. Conclusion: This DWI-based evaluation of capillary blood volume provides a noninvasive tool for predicting the postoperative renal function, thereby facilitating the management of UTUC patients.

The supine position improves but does not normalize the blunted pulmonary capillary blood volume response to exercise in mild COPD

Patients with mild chronic obstructive pulmonary disease (COPD) demonstrate resting pulmonary vascular dysfunction as well as a blunted pulmonary diffusing capacity (DLCO) and pulmonary capillary blood volume (VC) response to exercise. The transition from the upright to supine position increases central blood volume and perfusion pressure, which may overcome microvascular dysfunction in an otherwise intact alveolar-capillary interface. The present study examined whether the supine position normalized DLCO and VC responses to exercise in mild COPD. Sixteen mild COPD participants and 13 age-, gender-, and height-matched controls completed DLCO maneuvers at rest and during exercise in the upright and supine position. The multiple [Formula: see text]-DLCO method was used to determine DLCO, VC, and membrane diffusion capacity (DM). All three variables were adjusted for alveolar volume (DLCOAdj, VCAdj, and DMAdj). The supine position reduced alveolar volume similarly in both groups, but oxygen consumption and cardiac output were unaffected. DLCOAdj, DMAdj, and VCAdj were all lower in COPD. These same variables all increased with upright and supine exercise in both groups. DLCOAdj was unaffected by the supine position. VCAdj increased in the supine position similarly in both groups. DMAdj was reduced in the supine position in both groups. While the supine position increased exercise VCAdj in COPD, the increase was of similar magnitude to healthy controls; therefore, exercise VC remained blunted in COPD. The persistent reduction in exercise DLCO and VC when supine suggests that pulmonary vascular destruction is a contributing factor to the blunted DLCO and VC response to exercise in mild COPD. NEW & NOTEWORTHY Patients with mild chronic obstructive pulmonary disease demonstrate a combination of reversible pulmonary microvascular dysfunction and irreversible pulmonary microvascular destruction.