An MRI disc, typically a CD or DVD, contains the full digital record of a magnetic resonance imaging exam. The disc holds hundreds of image slices and the specialized software necessary to view them correctly on a personal computer. Accessing this media at home allows users to review the images or share them with a consulting physician. Viewing these files is for informational purposes only and must not be used as a substitute for a professional radiologist’s report or medical advice.
Accessing and Installing the Viewing Software
When the MRI disc is inserted, the computer often attempts to execute an autorun feature to start the viewing software automatically. If the viewer does not launch, manually navigate the disc’s file structure to locate the installation or executable file. This file is frequently found within a folder labeled “Viewer” and is often named something like `Viewer.exe` or `StartInteleViewerCD.exe`.
The software provided is usually a lightweight DICOM viewer designed to run directly from the media without a full installation, though some may require administrator permissions. Users with Apple computers may find the included viewer is PC-specific and need to download a compatible third-party DICOM viewer, such as OsiriX or Horos, to access the files. Once the viewer is running, it automatically searches the disc for the image files, which are stored in a standardized format.
Understanding the DICOM Standard
The digital images on the disc are stored using the Digital Imaging and Communications in Medicine (DICOM) standard, the universal protocol for medical imaging. DICOM files are fundamentally different from standard image formats like JPEG or PNG because they contain both the image data and extensive patient metadata. Standard picture viewers cannot open these files because they lack the necessary architecture to read and render the specialized data structure.
Each DICOM file includes a detailed header containing patient health information, such as the patient ID and study date, along with the technical parameters used during the scan. These acquisition parameters, which include details like slice thickness and the type of imaging sequence, are necessary for the viewer to display the images accurately. This standardized format ensures that imaging devices from different manufacturers can seamlessly communicate and share data. The viewing software interprets this metadata and presents the corresponding image data correctly.
Navigating the MRI Viewer Interface
After launching the viewer, the first step involves loading the specific study or series, which are often listed in a side panel. An MRI exam consists of hundreds of images, each representing a thin cross-section, or “slice,” of the body. To appreciate the three-dimensional anatomy, one must move sequentially through these slices, a process often controlled by scrolling the mouse wheel or using a dedicated scroll bar.
The viewer allows for the selection of different image sequences, which represent various ways the magnetic field and radiofrequency pulses were utilized during the scan. These sequences, such as T1-weighted, T2-weighted, or FLAIR, offer distinct visual contrasts of the tissue types. Selecting a different sequence changes the visual presentation of the study, highlighting different anatomical or pathological features.
A primary control for manipulating the visual display is the “Window” and “Level” function, which adjusts the contrast and brightness of the images. The “Level,” or window center, determines the brightness of the image, while the “Window,” or window width, controls the range of signal intensities displayed, effectively adjusting the contrast. By clicking and dragging the mouse across the image, the user can dynamically alter these parameters, revealing nuances in soft tissues that might otherwise be obscured.
Basic Principles of Image Interpretation
Understanding an MRI requires recognizing the three common anatomical planes used for imaging: axial, coronal, and sagittal. The axial plane divides the body into top and bottom sections, the coronal plane into front and back, and the sagittal plane into left and right. The viewing software typically displays these images with reference lines, which indicate the exact location and orientation of the view shown in another plane.
Image appearance is determined by signal intensity, a measure of the electromagnetic energy emitted by protons in tissues as they return to their resting state. Tissues with high signal intensity appear bright or white, while those with low signal intensity appear dark or black. Two common sequences, T1-weighted and T2-weighted, are differentiated by how they represent water and fat.
On a T1-weighted image, fat appears bright, and water or fluid, such as cerebrospinal fluid (CSF), appears dark. This sequence is better for appreciating normal anatomy and fat-containing structures. Conversely, on a T2-weighted image, both fat and water-based fluid appear bright. T2-weighted images are sensitive to fluid-containing abnormalities, like inflammation or edema, which appear as areas of increased brightness.