GRE vs True FISP Aortic Valve Artifacts: A Case Study

Aortic Valve

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Closed aortic valve during diastole True FISP.

Open aortic valve during systole True FISP.

Short axis view of the aortic valve True FISP sequence, notice artifact over valve.

Short axis view of the aortic valve GRE sequence same slice location.

GRE vs True FISP: Sequence Selection and Artifact Considerations

Choosing the appropriate imaging sequence is critical when evaluating the aortic valve. The comparison between Gradient Recalled Echo (GRE) and True Fast Imaging with Steady-state Precession (True FISP) sequences reveals important trade-offs that directly impact diagnostic quality.

GRE Sequences: Advantages for Aortic Valve Imaging

GRE sequences provide excellent spatial resolution and clear delineation of valve leaflets, making them ideal for assessing aortic valve morphology. The images demonstrate sharp anatomical detail with minimal flow-related artifacts. This sequence is particularly valuable when precise measurements of valve dimensions are required, as it offers consistent image quality across different cardiac phases.

True FISP Sequences: Benefits and Limitations

True FISP (also known as balanced SSFP or TrueFISP) offers superior blood-to-myocardium contrast and faster acquisition times. However, as evident in the comparison images above, True FISP sequences are susceptible to dark band artifacts, particularly over the aortic valve region. These artifacts result from local magnetic field inhomogeneities and can obscure critical anatomical details.

Clinical Implications

The presence of artifacts in True FISP imaging directly affects diagnostic confidence. When dark band artifacts overlay the valve leaflets, subtle pathology such as vegetations, small perforations, or leaflet calcifications may be missed. For this reason, GRE sequences are often preferred for dedicated aortic valve assessment, despite longer acquisition times.

SSFP systole aortic valve.

SSFP diastole aortic valve.

GRE aortic valve systole showing a forme fruste bicuspid aortic valve with partial fusion of the right and left coronary cusps.

GRE aortic valve diastole.

Clinical Case Example: How Artifacts Obscure Critical Pathology

The images above demonstrate a critical scenario where True FISP (SSFP) artifacts can completely obscure significant valve pathology, emphasizing why technologists must maintain attentiveness during image acquisition and quality review.

The SSFP Systole Image Problem

Examine the SSFP systole image (upper left). A prominent dark band artifact runs directly across the aortic valve, completely obscuring the valve leaflet anatomy. This artifact results from local field inhomogeneities and appears as a dark signal void that makes accurate morphological assessment impossible. In this critical systolic phase when the valve is open, the pathology is entirely hidden.

The SSFP Diastole Image

The SSFP diastole image (upper right) shows improved visualization with minimal artifact present during this cardiac phase. However, relying solely on diastolic images would miss crucial information about valve opening dynamics and systolic morphology.

The GRE Images Reveal the Pathology

Now examine the GRE systole image (lower left). Without any artifact interference, this image clearly reveals a forme fruste bicuspid aortic valve with partial fusion of the right and left coronary cusps. This congenital variant represents incomplete separation of two cusps, creating a raphe (indicated by the arrow on the image). The valve maintains a functional trileaflet appearance but has an underlying bicuspid anatomy.

The GRE diastole image (lower right) provides artifact-free visualization of the closed valve position, confirming the abnormal cusp morphology across all cardiac phases.

Clinical Significance and Technologist Responsibility

This case illustrates a scenario where critical pathology would be completely missed if:

• The technologist did not recognize the SSFP artifact during scanning

• Supplementary GRE images were not acquired

• Image quality was not reviewed before the patient left the scanner

• The radiologist only received SSFP sequences

Forme fruste bicuspid aortic valves are clinically significant because they:

• Carry similar risks to true bicuspid valves including accelerated degeneration

• May develop aortic stenosis or regurgitation earlier than normal tricuspid valves

• Require long-term surveillance

• May influence decisions about prophylactic valve replacement timing

• Are often underdiagnosed on echocardiography

This pathology would remain undetected without the technologist's decision to acquire GRE sequences when artifact was present, potentially delaying appropriate patient management and surveillance protocols.

Practical Recommendations

• Use GRE sequences as the primary method for detailed aortic valve morphology assessment

• Consider True FISP for functional evaluation when artifacts are minimal

• Adjust shim settings and center frequency to minimize True FISP artifacts when necessary

• When True FISP artifacts are present, always acquire supplementary GRE images

• Document sequence selection and any artifacts in the imaging report

Conclusion

Understanding the differences between GRE and True FISP sequences is essential for cardiac MRI technologists performing aortic valve imaging. While True FISP offers faster acquisition times and superior blood-myocardium contrast, its susceptibility to dark band artifacts can completely obscure critical valve pathology, as demonstrated in the clinical case of the forme fruste bicuspid valve presented above.

The technologist's role extends far beyond simply executing predetermined protocols. Active image quality monitoring, artifact recognition, and the clinical judgment to acquire supplementary GRE sequences when True FISP artifacts are present are critical skills that directly impact patient outcomes. A missed diagnosis of forme fruste bicuspid valve pathology can delay appropriate surveillance protocols and long-term management strategies.

By following the practical recommendations provided in this post, such as prioritizing GRE for morphological assessment, optimizing shim settings, acquiring additional sequences when artifacts are present, and documenting findings, technologists ensure a thorough diagnostic evaluation. Keep in mind that the extra time spent obtaining images free from artifacts is greatly outweighed by the clinical benefits of accurate pathology detection and appropriate patient care.