Fastspinecho

Fastspinecho, more commonly referred to as fast spin-echo (FSE), is an MRI pulse sequence designed to accelerate spin-echo imaging by collecting multiple lines of k-space within a single excitation. It provides T2-weighted contrast with greater efficiency than conventional spin-echo sequences and is widely used in clinical practice.

Principle: After the initial 90-degree excitation, a train of 180-degree refocusing pulses is applied, producing a series of echoes. Each echo fills one line of k-space, allowing several lines to be acquired per excitation. The turbo factor (echo train length) determines how many lines are obtained per trigger. Modern implementations use variable flip-angle refocusing to reduce energy deposition and minimize T2 blurring.

Variants and compatibility: Single-shot fast spin-echo acquires all lines in one shot for very rapid imaging, at the cost of reduced spatial resolution and increased T2 blurring if not carefully optimized. FSE sequences are frequently combined with fat suppression or fat saturation to enhance lesion conspicuity. FSE is less sensitive to magnetic field inhomogeneities than gradient-echo sequences, making it advantageous for regions near air-tissue interfaces.

Applications and limitations: FSE is widely used for brain, spine, musculoskeletal, and abdominal imaging where T2-weighted contrast is valuable. It offers shorter scan times and robust anatomy depiction, but longer echo trains can introduce T2 blurring and increased specific absorption rate (SAR). Trade-offs among ETL, repetition time, and flip angles are selected to balance image quality, speed, and patient safety.