On enhanced T 1 weighted images, finely dispersed areas of very low signal intensity became visible inside the tumour that correspond to areas of calcification ( Figure 1). The tumour shows moderate to marked enhancement. The vitreous may be abnormally bright on T 1 weighted images because of increased globulin content and a decreased ratio of albumin to globulin that occurs with malignancy. On T 1 weighted imaging, RB is slightly hyperintense to the vitreous. The partially calcified areas may appear as hypointense foci within the tumour on gradient-echo T 2 weighted and 3D FSE T 2 weighted images. It has a higher ability to visualise findings on T 2 weighted images such as vitreous seedings, higher contrast and SNR on post-contrast T 1 weighted images, and increased ability for 3D acquisitions with thin sections and higher resolution to better evaluate the optic nerve and the orbit.Īt T 2 weighted imaging, the tumour is usually dark compared with the vitreous. Application of parallel imaging has the potential to produce better quality diffusion weighted MRI and apparent diffusion coefficient (ADC) maps.ģ T MRI with dedicated multichannel head and neck coils will result in substantially higher contrast and SNR compared with 1.5 T scanner. Diffusion weighted images of the globe are obtained using a multislice spin-echo type of echo-planar imaging sequence with a gradient factor, b, of s mm −2. Constructive interference in steady state (CISS) sequence allow performance of multiplanar reconstruction to better demonstrate tumour extension. The additional sequences included short tau inversion-recovery (STIR) that can detect optic nerve infiltration. Finally, axial post-contrast T 1 weighted imaging of the brain is obtained. Contrast-enhanced fat suppression T 1 weighted MRI after intravenous injection of 0.1 mmol kg −1 gadopentate dimeglumine is done in axial and coronal planes as well as the parasagittal plane parallel to the long axis of the optic nerve. ![]() Pre- and post-contrast axial T 1 weighted MRIs with and without fat suppression are obtained. ![]() Gradient-echo T 2 weighted imaging has been shown to be a more effective sequence to detect calcified structures. ![]() High-resolution three-dimensional (3D) FSE T 2 weighted imaging allows thin sections (0.4 mm) with high SNR that is sensitive to the detection of calcification. įast spin echo (FSE) T 2 weighted imaging is used for the evaluation of the globe, but it has limited ability to detect calcification. Sedation with oral chloral hydrate used for infants and children 4 years of age and younger and intramuscular ketamine for children from 5–8 years of age is administrated. The surface coil is a circular polarising coil with a diameter of 4 cm positioned 1 cm above the eye. The head coil is commonly used however, the application of the surface coil improves the signal-to-noise ratio (SNR) of the globe. MRI of the globe is commonly done at 1.5 T. The aim of this article is to review the role of MRI in RB. Also, it helps to differentiate RB from simulating lesions presenting with leukocoria. MRI is becoming an increasingly important tool for monitoring focal response to therapy. It can detect the growth pattern of the tumour and determine the extension of the tumour, the involvement of the optic nerve and retrobulbar space, the presence of leptomeningeal spread or the existence of a second tumour. MRI should be used to answer the key clinical questions that help in the selection of an appropriate line of treatment. ![]() The tumour extension is not well delineated with ultrasound. RB appears as a solid echogenic mass with high echogenic foci of calcifications on ultrasound studies. RB is one of the most challenging problems in paediatric ophthalmology and radiology because it shows different patterns of growth, extension and recurrence. It is a highly malignant tumour of the primitive neural retina. Retinoblastoma (RB) is the most common intraocular tumour of childhood.
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