MRI Concepts and Components

The difference in signal intensity between two different tissues or structures.

A high signal intensity on an MRI image, appearing white.

A low signal intensity on an MRI image, appearing black.

A measure of the strength of the MRI signal compared to the background noise.

A measure of how well different tissues can be distinguished from each other on an MRI image.

The level of detail in an MRI image, measured in the number of pixels per unit area.

The time it takes to acquire MRI data, often measured in minutes.

A set of instructions for acquiring MRI images, defining parameters like echo time and repetition time.

Areas with high proton density (e.g., the pelvis) have higher SNR than areas with low proton density (e.g., the lungs).

Larger coils pick up more noise relative to signal, while smaller coils have better SNR.

Quadrature coils and phased array coils improve SNR by combining signals from multiple receiver coils.

Placing the coil perpendicular to the magnetic field (B0) maximizes SNR.

Longer TR allows more time for longitudinal magnetization to recover, increasing SNR.

Flip angle determines the amount of transverse magnetization produced, influencing signal strength.

A 90° flip angle with a long TR maximizes signal amplitude by fully converting longitudinal magnetization into transverse magnetization.

Signal originates from the patient, occurring at specific frequencies and times related to the magnetic field strength. It can be manipulated to enhance image quality.

Noise is random, unpredictable, and occurs at all frequencies. It comes from thermal motion in the patient and background electrical noise. It can't be controlled as easily as signal.

The strength of the magnet directly influences SNR. Stronger magnets produce a stronger signal, improving image clarity.

Different types of coils affect signal collection efficiency, influencing the SNR. Placement also matters.

The repetition time (TR), echo time (TE), and flip angle influence how much signal is collected and how it's affected by noise, impacting SNR.

Averaging multiple scans improves the signal-to-noise ratio by reducing the effect of random noise.

The volume of a single 3D picture element (voxel) in an MRI image, directly impacting the quality of the image.

The time it takes for the transverse magnetization to decay to 37% of its initial value. It affects the contrast of MR images by influencing the amount of signal from different tissues.

The ratio of signal intensity to noise level. A higher SNR means a better quality image with less noise.

The angle at which the magnetization is flipped by the radiofrequency pulse. It influences the signal strength.

The magnetic field strength, measured in Tesla (T). It affects the signal strength and image resolution.

The number of times a signal is acquired and averaged. Increasing NEX reduces noise and improves image quality.

The bandwidth of frequencies acquired during signal acquisition. Narrower bandwidth increases SNR but slows down acquisition.

The smallest unit of volume represented in the MR image, containing spins contributing to the signal. Larger voxels have higher SNR, smaller voxels have better resolution.

The repetition time is the time between two consecutive radiofrequency pulses. It affects the strength and contrast of the MR image.