Our teaching poster aims to provide a comprehensive pictorial guide that helps to navigate through the common MRI sequence types used by two major manufacturers, Siemens and GE. By providing side-by-side comparisons of these sequences and their names, we intend to enhance interpretation and understanding for medical professionals using these systems. In addition, we will discuss the image processing techniques that allow for achieving the same or nearly the same image appearances on both manufacturers' platforms.

Table 1: Terminology summary of Siemens MRI and GE MRI sequences

MRI sequences can be divided into four main categories: spin echo (SE), gradient echo (GRE), inversion recovery (IR), and echoplanar imaging (EPI). Numerous sequence variations are available for clinical applications within these four categories. Our poster focuses on the sequences most commonly used in clinical practice. [1]

Both manufacturers refer to conventional spin echo sequences as SE, with no manufacturer-specific naming conventions. [1] [3]

One modification of the SE (spin echo) sequences is the Fast Spin Echo (FSE) sequence, which consists of a 90° radiofrequency pulse followed by multiple 180° pulses within each repetition time. Siemens refers to this sequence as Turbo Spin Echo (TSE), while GE calls it Fast Spin Echo (FSE). There are minimal differences in their applicability and image appearance. [1] [2]

Fig 1: Comparison of GE FSE and SIEMENS TSE sequences

Another modification is the Single-shot multi-SE, a type of FSE where all the k-space lines required to form an image are acquired within a single repetition time (single-shot), while slightly more than half of the k-space is filled. These two factors make this sequence extremely fast. GE refers to this sequence as SSFSE (Single-Shot Fast Spin Echo), while Siemens labels it HASTE (Half-Fourier Acquisition Single-shot Turbo Spin Echo). [1] [4]

Fig 2: Comparison of GE SSFSE and SIEMENS HASTE sequences

Two similar gradient echo (GRE) sequences are Siemens VIBE and GE LAVA. Siemens VIBE (Volume Interpolated Breath-hold Examination) is a 3D gradient echo sequence optimized for high-resolution abdominal and pelvic imaging. It allows for breath-hold acquisitions and provides excellent tissue contrast, making it particularly useful for contrast-enhanced studies such as liver imaging. GE LAVA (Liver Acquisition with Volume Acceleration) is a similar 3D gradient echo sequence designed for high-resolution liver imaging. LAVA also enables breath-hold imaging and is commonly used in dynamic contrast-enhanced MRI to assess the liver and surrounding structures. [5]

Both sequences can utilize the Dixon technique, which separates fat and water signals by acquiring multiple echoes with different echo times (TEs). This technique generates four types of images:

In-phase: Fat and water protons are in sync, and their signals add together, creating a combined tissue contrast.

Out-of-phase: Fat and water protons are in opposite phases, leading to signal cancellation at fat-water interfaces, which helps in detecting fatty infiltration or microscopic fat content.

Fig 3: In-phase and out-of phase images

Water-only: The fat signal is suppressed, displaying only water-containing tissues and improving lesion detection.

Fig 4: Comparison of GE LAVA and SIEMENS VIBE sequences (Water-only)

Fat-only: The water signal is suppressed, highlighting fat-containing structures and aiding in the assessment of fat distribution.

Fig 5: Comparison of GE LAVA and SIEMENS VIBE sequences (Fat-only)

By providing these four image sets, the Dixon technique enables more accurate fat quantification, better tissue differentiation, and improved fat suppression compared to conventional in-phase and out-of-phase imaging. [6]

The CISS (Constructive Interference in Steady State) and FIESTA-C (Fast Imaging Employing Steady State Acquisition with Cyclic Rephasing) sequences belong to the steady-state free precession (SSFP) type of MR sequences. These methods are primarily used for imaging fine anatomical structures, particularly the brain and spinal cord, as well as the inner ear and small blood vessels and nerves. Iso-intense structures (e.g., nerves and vessel walls) can be easily distinguished from cerebrospinal fluid (CSF) or other fluid backgrounds. [7]

Fig 6: Comparison of GE FIESTA-C and SIEMENS CISS sequences

The SIEMENS TrueFISP (True Fast Imaging with Steady-State Precession) and GE FIESTA (Fast Imaging Employing Steady-State Acquisition) are classified as fast sequences and generally provide excellent tissue contrast, high spatial resolution, and short acquisition times. Both are steady-state sequences, balancing T1 and T2 relaxation, and are ideal for imaging moving organs like the heart and abdomen. Due to the excellent contrast difference, they are popular in cardiac imaging, as they provide excellent contrast between the heart chambers and blood. They are also used in neurological and orthopedic imaging and MR cholangiography. [8]

Fig 7: Comparison of GE FIESTA and SIEMENS True-FISP sequences

The Siemens MR TIRM (Turbo Inversion Recovery Magnitude) and the GE MR STIR (Short Tau Inversion Recovery) sequences suppress fat and highligt inflammation, oedema, or other pathologies. Both use the inversion recovery (IR) technique, where a 180° RF pulse is applied to invert the magnetization of tissues. The inversion time (TI) is selected to nullify the fat signal. [9]

TIRM is a type of turbo spin-echo (TSE) sequence, meaning it applies accelerated imaging technology, resulting in faster imaging. TIRM is Siemens' proprietary implementation, while STIR is available from multiple manufacturers, including GE. In addition to TIRM, Siemens MR systems also feature a traditional STIR sequence. The STIR sequence also uses the inversion recovery technique, but the TI is set to a short value to selectively suppress the fat signal. This sequence is not based on turbo spin-echo but can be either simple spin-echo or fast spin-echo. [9]

Fig 8: Comparison of GE STIR and SIEMENS TIRM sequences

The Siemens MR BLADE and GE PROPELLER sequences use similar technology in MRI imaging, aimed at reducing motion-induced artifacts and improving image quality. Both sequences can be used in neurological, orthopedic, and cardiological imaging. They can be applied with different contrasts, such as T1, T2, or FLAIR imaging.

The BLADE sequence is based on the so-called "radial sampling" technology, where data is collected not in the conventional k-space (rectilinear pattern), but in concentric circles or blade-like slices (referred to as "blade"). [10]

The PROPELLER sequence also uses the "radial sampling" technique, where data is gathered in blade-like blocks. The term "propeller" refers to the fact that the data acquisition pattern resembles a rotating propeller blade. [11]

Fig 9: Comparison of GE PROPELLER and SIEMENS BLADE sequences

The Siemens MR SWI (Susceptibility Weighted Imaging) and GE MR SWAN (Susceptibility Weighted Angiography) sequences operate on similar principles. Both sequences are designed for the sensitive detection of paramagnetic substances present in tissues, such as deoxyhemoglobin, hemosiderin, ferritin, or the iron and calcium content of tissues. These substances cause local magnetic field changes, resulting in characteristic signals on MR images.

These sequences provide high contrast between iron-rich tissues or blood degradation products and normal tissues, in the form of lower signal intensity. They are especially useful for imaging brain microbleeds, vascular malformations (e.g., cavernomas), traumatic brain injuries, iron and calcium accumulation, and for evaluating neurodegenerative diseases (e.g., Parkinson’s disease or Alzheimer’s disease). [12][13]

Fig 10: Comparison of GE SWAN and SIEMENS SWI sequences

The GE BRAVO (Brain Volume Imaging) and Siemens MPRAGE (Magnetization Prepared Rapid Acquisition Gradient Echo) sequences are both 3D T1-weighted MRI sequences for brain imaging, neuroimaging, and post-contrast studies. These sequences provide excellent gray-white matter contrast. Their applications include the diagnosis of Alzheimer's disease, multiple sclerosis (MS), and other neurodegenerative disorders. [14][15]

Fig 11: Comparison of GE BRAVO and SIEMENS MPRAGE sequences

GE and Siemens MRI devices are equipped with advanced imaging and reconstruction technologies that are capable of producing high-quality images not only in standard coronal and sagittal planes but also in arbitrary oblique planes.

Fig 12: Manual multiplanar reconstructions from 3DT1-weighted axial images

Both manufacturers allow automatic 3D image reconstructions, which helps radiographers by removing the need for time-consuming post-processing after the scans.

During MR angiography and MRCP procedures, in addition to automatic and manual image rotation, spatial reconstructions are possible, such as maximum intensity projection (MIP) or volume rendering (VR) techniques, which further enhance the visualization of vascular and biliary structures. These technologies are especially useful for depicting complex anatomical structures, such as tumors, vascular malformations, or biliary strictures.

Fig 13: Automatically reconstructed MRCP sequence