Patient’s demographic data
This prospective study included 61 patients (30 male and 31 female) with an age range from 5 to 72 years (mean ± SD = 41.35 ± 15.62). MRI studies for all cases were performed in the period from June 2020 to November 2021. This study was approved by our institution ethics committee and informed written consent was obtained from each patient.
Patients presented by variable neurological conditions including:
Suspected infection (Fever, disturbed conscious level, neck stiffness).
Patients with clinical suspicion of multiple sclerosis (numbness, limb weakness, fatigue, gait disturbance and visual symptoms) or on follow-up to assess activity of disease.
Patients with suspected primary brain tumor or on post-operative / post radiotherapy follow-up.
Patients with known elsewhere primary brain tumor with underlying metastatic work up to detect metastatic brain lesions.
General contra-indications for MRI scan, for example:
Patients who have a cardiac pacemaker.
Patients with cochlear implants.
Patients having an intracranial aneurysmal clip.
Un-cooperative and claustrophobic patients.
Bad general condition.
Patients who have contraindications to contrast media as in severely impaired renal function for the fear of nephrogenic systemic sclerosis and other complications of IV Gadolinium contrast media.
MRI examinations were performed for all patients using 1.5 T. MRI unit (Philips Interna) with standard head coil and with the patient in supine position. The following sequences were obtained for all patients: fast spin echo (FSE) T1WI (TR/TE: 581/15 ms, slice thickness: 5 mm, interslice gap: 1 mm, flip angle: 69, FOV: 230 mm and matrix: 256), T2WI (TR/TE: 4000/100 ms, slice thickness: 5 mm, interslice gap: 1 mm, flip angle: 90, FOV: 230 mm and matrix: 256), FLAIR (TR/TE: 11,000/110 ms, TI: 2800 ms, slice thickness: 5 mm, interslice gap: 1 mm, flip angle: 90, FOV: 230 mm and matrix: 256) and DWI (TR/TE: 3614/160 ms, TI: 2800 ms, slice thickness: 5 mm, interslice gap: 1 mm, flip angle: 90, FOV: 230 mm and matrix: 256).
Contrast enhanced images were acquired after intravenous injection of Gadolinium (Magnevist) in the dose of 0.1 mmol/kg body weight. One minute after the injection of contrast agent, the acquisition of axial, sagittal and coronal conventional CE-T1WI were immediately done, the axial or coronal CE-FLAIR images were acquired successively with a delay time of approximately 3–4 min (the scan parameters were the same as the pre-contrast images).
MR images were analyzed independently by two experienced radiologists with about 14 and 10 years’ experience in neuroimaging.
At first the radiologists interpret the conventional MRI sequences to detect any brain lesion (e.g., tumor, infection, multiple sclerosis (MS), etc.). Then CE-T1WI and CE-FLAIR images were assessed and compared with each other’s. Images were assessed both qualitatively and quantitatively.
If CE-FLAIR images were unable to differentiate enhancing lesion from surrounding edema (as in tumors) or unable to detect lesion enhancement as in lesions with initially high signal intensity (SI) in pre contrast FLAIR images especially in cases of MS, we use subtraction MRI technique by performing a subtraction between the post-contrast and the corresponding pre-contrast FLAIR images to evaluate and confirm the presence of enhancement. Subtraction technique was added in most of the cases of our study (39 cases).
Qualitative evaluation by visual assessment includes the following:
Existence of lesion contrast enhancement.
Defining the site and pattern of lesion enhancement.
Estimation of the lesion rate of enhancement in both CE-T1WI and CE-FLAIR and classing it in CE-FLAIR images as: superior, equivocal or inferior comparing to CE-T1WI.
Assessment of lesion conspicuity which was defined as delineation of the border of the enhanced lesion in CE-FLAIR images and differentiating the lesion from the surrounding edema or from the normal appearing brain parenchyma, it was classified into: no, fair or good delineation.
Linking the images findings with the provided clinical data.
Quantitative evaluation includes the following items:
It was done by measuring the SI of the lesion in both pre and post contrast FLAIR images by using region of interest (ROI). It was calculated by using the following equation: Iˆ = I − I0 (Iˆ is CEI, I is the lesion SI on CE-FLAIR images and I0 is the lesion SI on pre-contrast FLAIR images).
It was done by measuring the lesion SI as well as the background SI in normal appearing brain parenchyma by using ROI and applied to pre and post contrast T1W images as well as pre and post contrast FLAIR images. The lesion to background contrast ratio was calculated by using the following equation: Lesion to background contrast ratio = Lesion SI − Background SI/Background SI.
Standard of reference
In our study histopathology was used as a standard of reference in all included cases of space occupying lesions. In cases of MS we used clinical findings and CSF analysis as our standard of reference, while in cases of infection, we used the clinical and laboratory findings as a standard of reference.
Statistical analysis and data interpretation
Data were fed to the computer and analyzed using IBM SPSS Corp. Released 2013. IBM SPSS Statistics for Windows, Version 22.0. Armonk, NY: IBM Corp. Qualitative data were described using number and percent. Quantitative data were described using median (minimum and maximum) for non-parametric data and mean, standard deviation for parametric data after testing normality using Kolmogorov–Smirnov test. Significance of the obtained results was judged at the (0.05) level. The diagnostic performance of a test was evaluated using Receiver Operating Characteristic (ROC) curve analysis. Sensitivity and Specificity were detected from the curve and PPV, NPV and accuracy were calculated through cross tabulation. Inter-class correlation was used to detect agreement between continuous variables with correlation coefficient more than 0.7 was considered excellent agreement. Kappa agreement was calculated by cross tabulation for categorical variables with Kappa of 0.81–0.99 was considered Perfect agreement.