MRI Pulse Sequences and Image Contrast

A type of MRI sequence that uses multiple 180-degree pulses after a 90-degree pulse to obtain multiple echoes per TR. This allows for faster acquisition and reduces scan time.

A modified spin echo sequence where two 180-degree pulses are used after each 90-degree pulse, resulting in two echoes per TR.

The number of 180-degree pulses sent after each 90-degree pulse in an FSE sequence. It determines the speed of acquisition and the T1 weighting of the image.

The time between the 90-degree pulse and the center of the K-space filling in an FSE sequence. It influences the T1 and T2 weighting of the images.

A fast spin echo sequence that acquires all the echoes needed to form an image in a single TR. It's extremely fast but often results in lower image quality.

A type of MRI sequence that uses a single 180-degree pulse after a 90-degree pulse. It's slower than FSE but provides higher image quality.

A common MRI sequence that highlights tissues with high water content, making it useful for detecting edema and fluid collections.

A common MRI sequence that highlights anatomical structures with high fat content, making it useful for visualizing anatomy.

A type of MRI sequence that doesn't use a 180-degree pulse for rephasing, instead relying on gradient reversal.

In GRE sequences, while the flip angle is smaller, there is early recovery of longitudinal magnetization, allowing for reduced TR (repetition time) and faster scanning.

T2* relaxation in GRE is a combination of true T2 relaxation and dephasing caused by magnetic field inhomogeneity, unlike SE sequences where the 180-degree pulse eliminates this inhomogeneity.

GRE sequences where the residual transverse magnetization is destroyed or nullified after signal reception.

GRE sequences where the residual transverse magnetization is not destroyed but refocused to achieve a steady state after multiple TRs.

In SS GRE sequences, the repetition time (TR) is shorter than the T1 and T2 relaxation times of the tissues, resulting in coexistence of both longitudinal and transverse magnetization.

Most gradient echo sequences utilize the steady state mode, where TR is shorter than T1 and T2, allowing for faster imaging.

A pulse sequence in MRI is a specific series of radiofrequency pulses and gradient fields applied to the patient to generate an image. It dictates how the MR signal is acquired and what type of image contrast is generated.

Pulse sequences can be broadly divided into two main categories: Spin Echo (SE) sequences and Gradient Echo (GRE) sequences. These categories differ in how they manipulate the magnetic field and acquire the MR signal.

A Spin Echo (SE) sequence relies on 90° and 180° radiofrequency pulses to generate a spin echo signal. The 90° pulse flips the net magnetization into the transverse plane, and the 180° pulse re-phases the spins, creating a stronger signal.

The time between two 90° pulses in an SE sequence is called Repetition Time (TR), and the time between the 90° pulse and the echo reception is called Echo Time (TE).

Slice selection gradient is applied during RF pulse transmission to define the slice being imaged. Phase encoding gradient is applied between the 90° pulse and signal measurement to encode spatial information.

A Dual Spin Echo (DSE) sequence generates two echoes from a single excitation pulse. This allows for different contrast weighting in the same image. It's essentially applying two SE sequences within a single TR.

A Fast Spin Echo (FSE) or Turbo Spin Echo sequence utilizes multiple 180° pulses to generate multiple echoes in each TR. This speeds up the imaging process by acquiring multiple echoes in a shorter time.

A Single-Shot Fast Spin Echo (SSFSE) sequence acquires all the data needed for an image in a single TR. It's very efficient for fast imaging but may have some limitations due to reduced signal to noise ratio.

A type of MR pulse sequence that uses an inversion pulse to suppress signals from specific tissues.

A variation of the IR sequence that uses a short TI value to suppress fat signals.

A variation of the IR sequence that utilizes a long TI value to suppress fluid signals.

An MR imaging technique that accelerates acquisition by filling all lines of K-space within one TR.

A type of EPI sequence where all k-space lines are acquired in a single TR.

A dynamic MR imaging technique using GRE or EPI sequences with contrast enhancement to study contrast uptake by lesions.

This MRI technique uses gradients to re-phase spins in the EPI sequence.

This type of EPI sequence uses multiple 180-degree pulses to generate echoes.

A type of MRI imaging used to identify areas where the movement of extracellular water is restricted, often indicating damaged tissue. An example of a common use is detecting infarcted tissue in the brain after a stroke.

A dynamic MRI technique that captures images of the brain during activity and at rest, allowing researchers to study brain function.

A technique in MRI used to suppress background tissue noise, enhancing the visibility of blood vessels and certain disease processes.

An MRI technique that provides high-resolution images of blood vessels, distinguishing between moving (blood flow) and stationary tissues.

A type of MRA that utilizes coherent GRE pulse sequences, saturating background tissue while allowing flowing spins to show high signal intensity. Useful for visualizing arteries and veins.

A type of pulse sequence that uses a variable flip angle excitation pulse and frequency encoding gradient rephasing to produce a gradient echo. It then spoils or dephases the residual transverse magnetization to minimize its effect on image contrast.

A pulse sequence that uses a 180-degree inversion pulse before the standard spin-echo or gradient echo sequence. This pulse flips the longitudinal magnetization (LM) from positive to negative, saturating the tissues. The LM then recovers gradually along the positive Z-axis, with different recovery rates for different tissues depending on their T1 values.

The time interval between the inverting 180-degree pulse and the excitatory 90-degree pulse in an Inversion Recovery (IR) sequence.

The time it takes for tissues to lose 63% of their longitudinal magnetization (LM) after a 90-degree excitation pulse. It is a characteristic property of each tissue.

A type of pulse sequence that utilizes steady-state conditions, meaning the magnetization reaches an equilibrium after repeated excitation pulses. It typically uses short repetition times (TR) and echo times (TE).

The time interval between successive excitation pulses in a pulse sequence.

The time interval between the excitation pulse and the echo signal in a pulse sequence.

A type of gradient echo sequence that exploits the properties of steady-state magnetization. It provides good T2 weighting and is particularly useful for acquiring images quickly.