Diffusion-Weighted Echoplanar Imaging Prevails in Hepatic Metastasis Diagnosis

The objective of a recent study was to assess the value of respiratory-triggered,
diffusion-weighted single-shot echoplanar MRI in the diagnosis of hepatic
metastatic disease when compared to T2-weighted turbo spin-echo sequences.

The results have shown that diffusion-weighted echoplanar imaging is more sensitive and accurate
than T2-weighted turbo spin-echo sequences, particularly in the detection of
metastatic lesions measuring <10 mm.

Design
Retrospective analysis.

Participants/Methodology
This study was comprised of 52 patients (30 men and 22 women) with extrahepatic primary
malignant neoplasms who were evaluated with MRI. There were 118 metastatic
lesions discovered in 28 patients. Twenty patients had benign lesions comprised
of hemangiomas and cysts. The remaining 4 patients had no evidence of hepatic
lesions.

Thirty-four metastases and 3 hemangiomas had histopathological results. Diagnosis of the
remaining 84 metastases, 54 hemangiomas, and 49 cysts was made with
characteristic imaging criteria on unenhanced and dynamic-enhanced MRIs.

MRI was performed with a 1.5-T system. Imaging sequences included respiratory-triggered
diffusion-weighted echoplanar and five T2-weighted turbo spin-echo sequences.
These were breath-hold fat-suppressed half-Fourier acquisition single-shot
turbo spin-echo (HASTE), breath-hold and respiratory-triggered fat-suppressed
turbo spin-echo, and breath-hold and respiratory-triggered short inversion
recovery.

Dynamic contrast-enhanced three-dimensional gradient-echo sequences were also
performed. Diffusion-weighted imaging was obtained with b-values of 50, 300,
and 600 seconds/mm2. MRIs were evaluated independently by two radiologists
unaware of other imaging findings or histopathology.

Results
The diffusion-weighted echoplanar sequence was found to be significantly more
accurate in the diagnosis of metastatic lesions of all sizes than the
T2-weighted turbo spin-echo sequences. When comparing individual T2-weighted
turbo spin-echo sequences, the HASTE sequence was found to be less accurate and
statistically significantly less sensitive than the other T2-weighted
sequences.

The increased sensitivity of diffusion-weighted echoplanar imaging compared to the
T2-weighted turbo spin-echo sequences was even more pronounced when only
lesions measuring <10 mm in size were considered.

Reviewer’s
Comments
The results of this study are useful in demonstrating that diffusion-weighted echoplanar MRI
is more sensitive and more accurate than T2-weighted turbo spin-echo sequences
in the diagnosis of hepatic metastatic disease. This is especially evident with
lesions measuring <10 mm. Therefore, it would be advantageous to incorporate
this into a standard abdominal MRI protocol.

An additional important observation is that the HASTE sequence is less sensitive and less
accurate than the other T2-weighted turbo spin-echo sequences. One of the limitations
reported in this study was a small number of lesions with histopathologic
confirmation.

Author:
John C. Sabatino, MD, MSD

Reference:

Bruegel M, Gaa J,
et al: AJR; 2008;191 (November): 1421-1429:
Diagnosis of Hepatic Metastasis: Comparison of Respiration-Triggered Diffusion-Weighted
Echo-Planar MRI and Five T2-Weighted Turbo Spin-Echo Sequences.