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We developed a semi-automated volumetric software, NPerfusion, to segment brain tumors and quantify perfusion parameters on whole-brain CT perfusion (WBCTP) images. The purpose of this study was to assess the feasibility of the software and to validate its performance compared with manual segmentation. Twenty-nine patients with pathologically proven brain tumors who underwent preoperative WBCTP between August 2012 and February 2015 were included. Three perfusion parameters, arterial flow (AF), equivalent blood volume (EBV), and Patlak flow (PF, which is a measure of permeability of capillaries), of brain tumors were generated by a commercial software and then quantified volumetrically by NPerfusion, which also semi-automatically segmented tumor boundaries. The quantification was validated by comparison with that of manual segmentation in terms of the concordance correlation coefficient and Bland-Altman analysis. With NPerfusion, we successfully performed segmentation and quantified whole volumetric perfusion parameters of all 29 brain tumors that showed consistent perfusion trends with previous studies. The validation of the perfusion parameter quantification exhibited almost perfect agreement with manual segmentation, with Lin concordance correlation coefficients (ρ c) for AF, EBV, and PF of 0.9988, 0.9994, and 0.9976, respectively. On Bland-Altman analysis, most differences between this software and manual segmentation on the commercial software were within the limit of agreement. NPerfusion successfully performs segmentation of brain tumors and calculates perfusion parameters of brain tumors. We validated this semi-automated segmentation software by comparing it with manual segmentation. NPerfusion can be used to calculate volumetric perfusion parameters of brain tumors from WBCTP.

Respiratory syncytial virus (RSV) is a common pathogen causing acute respiratory infection in children. Herein, we describe the incidence and clinical and magnetic resonance imaging (MRI) findings of RSV-related encephalitis, a major neurological complication of RSV infection.We retrospectively reviewed the medical records and imaging findings of the patients over the past 7 years who are admitted to our medical center and are tested positive for RSV-RNA by reverse transcriptase PCR. In total, 3,856 patients were diagnosed with RSV bronchiolitis, and 28 of them underwent brain MRI for the evaluation of neurologic symptoms; 8 of these 28 patients had positive imaging findings. Five of these 8 patients were excluded because of non-RSV-related pathologies, such as subdural hemorrhage, brain volume loss due to status epilepticus, periventricular leukomalacia, preexisting ventriculomegaly, and hypoxic brain injury.The incidence of RSV-related encephalitis was as follows: 3/3,856 (0.08 %) of the patients are positive for RSV RNA, 3/28 (10.7 %) of the patient underwent brain MRI for neurological symptom, and 3/8 (37.5 %) of patients revealed abnormal MR findings. The imaging findings were suggestive of patterns of rhombenmesencephalitis, encephalitis with acute disseminated encephalomyelitis, and limbic encephalitis. They demonstrated no diffusion abnormality on diffusion-weighted image and symptom improvement on the follow-up study.Encephalitis with RSV bronchiolitis occurs rarely. However, on brain MRI performed upon suspicion of neurologic involvement, RSV encephalitis is not infrequently observed among the abnormal MR findings and may mimic other viral and limbic encephalitis. Physicians should be aware of this entity to ensure proper diagnosis and neurologic care of RSV-positive patients.

Dear Sir, We thank Dr. Donmez for his comments on our publication in Neuroradiology [1], and we would like to make the following comments in reply. He noted that the normal diffusion-weighted imaging (DWI) of our cases may not be associated with a good prognosis if brain magnetic resonance imaging (MRI) with diffusion study was performed in the subacute phase of cytotoxic edema, in which restricted diffusion start to diminish and apparent diffusion coefficient (ADC) values increase. We agree with him that timing is important in brain MRI with diffusion study in patients with encephalitis, and DWI may be less sensitive when there is a time delay between the onset of the disease and imaging. In all three of our cases, the pediatric physicians decided to performDWIwithin the first 12 h and conventional brainMRI within the first 3 days immediately after meaningful neurologic symptom onset. There was no definite restriction on the diffusion study including ADC map in our cases. So we could not find the evidence of cytotoxic edema induced by encephalitis at acute phase in our cases by using diffusion study [2]. As we expected, these patients showed favorable outcome with supportive management. In a previous report, enterovirus 71-related encephalomyelitis with brainMRI and DWI study, we experienced that four of five patients did not reveal definite restriction on the diffusion study, who gradually recovered with conservative treatment without sequelae. But, one case with restricted diffusion in the lesion of the hippocampus showed the atrophic change on follow-up study [3]. Consequently, we consider that no definite restriction on the diffusion study in the early phase of the RSV-related encephalitis may provide evidence for the reversibility of the lesion, which is not progressed to cytotoxic edema and it is associated with favorable outcomes [4, 5]. As Dr. Donmez commented, DWI is superior to conventional MRI in detecting irreversible cytotoxic edema especially at acute phase of encephalitis. However, it may be less sensitive at later phase due to dynamic pathologic changes. It is needed to be considered and discussed at further study.