Edema-Correction is Essential for Monitoring Brain Atrophy with BPF
Marcel Warntjes1,2, Anders Tisell1,3, Irene Håkansson4, and Peter Lundberg1

1Center for Medical Imaging Science and Visualization, Linköping, Sweden, 2SyntheticMR AB, Linköping, Sweden, 3Department of Medical and Health Sciences, Radiation Physics, Linköping, Sweden, 4Department of Clinical and Experimental Medicine, Neurology, Linköping, Sweden


The rate of brain atrophy in neuro-degenerative diseases is monitored using the brain parenchymal fraction (BPF, the ratio of brain volume and intracranial volume). The true atrophy, however, may be obscured by the simultaneous brain swelling due to inflammatory processes, disease activity and medication. Measurement of the average relaxation rates and proton density of the brain allows correction for the presence of edemic water. The edema-corrected BPF showed a higher rate of atrophy, 0.495%/year (p = 0.003), in comparison to the uncorrected BPF, 0.175%/year (p = 0.12), in a group of early-onset Multiple Sclerosis patients.


To correct brain volumetric measurements, determined by the brain parenchymal fraction (BPF), for the presence of edema. The brain may be more or less swollen due to inflammatory processes, disease activity and medication. Volume changes of the brain due to edemic water may obscure the true rate of atrophy or lead to a large variation in BPF values during follow-up.


In the prospective study 10 relatively young patients were included after a first relapse, suggestive of Multiple Sclerosis (Clinically Isolated Syndrome, CIS). Their mean age was 32±10 years at inclusion. The mean longitudinal R1 rate, the mean transverse R2 rate and the mean proton density PD of the entire brain was measured using the Qrapmaster method [1]. Measurement of brain volume BPV, intracranial volume ICV and the ratio BPF was performed by SyMRI (SyntheticMR,Linköping, Sweden). The patients were measured at base-line, and at 1, 2 and 4 years follow-up. Also 10 healthy controls were included (mean age 38±5) to determine a (single) reference brain R1ref, R2ref and PDref values. The presence of edema was estimated using an edema fraction EF


where CSF values were taken from Ref. 1. The edema-corrected EC-BPF was then calculated as


All scans were performed with a Philips 1.5T Achiva system (Philips Healthcare, Best, the Netherlands).


The reference brain values were determined at R1ref = 1.125 s-1, R2ref = 11.091 s-1 and PDref = 76.393%. The average BPF and EC-BPF of all patients at baseline and follow-up is shown in Table 1. All data points are shown in Fig. 2, as the relative difference compared to baseline. Linear regression showed that uncorrected BPF decreased with a non-significant 0.175% per year (95% confidence interval [-0.373, 0.043], p = 0.12), whereas the EC-BPF decreased with a significant 0.495% per year (95%CI [-0.805, -0.184] (p = 0.003).

Discussion and conclusion

The results show that BPF may vary substantially in the first years after the onset of MS, which may be due to the presence of edema, partial recovery, difference in disease actively (Relapse-Remitting) and effects of medication. The variation may be strongest for relatively young patients, early their disease. Edema may obscure the true rate of atrophy in the BPF measurements. Edema correction of BPF may produce a more reliable and robust method of monitoring brain atrophy in neuro-degenerative diseases.


No acknowledgement found.


[1] Warntjes et al. Magn Reson Med 60; 320-329(2008)


Table 1. The observed BPF and edema-corrected EC-BPF at all time-points

Fig. 2. BPF (blue dots ) and EC-BPF (red dots) of the included 10 patients as a function of time after inclusion. Linear regression slopes are shown for BPF (blue line) and EC-BPF (red line).

Proc. Intl. Soc. Mag. Reson. Med. 24 (2016)