Inversion-recovery (IR) imaging has made significant strides in brain MR, offering higher T1-weighted contrast and improving the contrast ratio of tumor to white matter. But IR imaging still cannot best spin-echo (SE) MRI for detecting brain metastases, according to radiologists from China. They compared the two MR protocols in 31 patients treated at the First Affiliated Hospital of Anhui Medical University in Hefei.
Dr. Yong-Qiang Yu and colleagues hypothesized that pre- and postcontrast T1-weighted inversion-recovery MRI would have superior sensitivity to pre- and postcontrast T1-weighted spin echo. The majority (16) of the 31 patients had lung cancer as the primary neoplasm.
Imaging was done on a 1.5-tesla system (Signal Horizon, GE Healthcare, Chalfont St. Giles, U.K.). T1-weighted inversion recovery was obtained with a fast SE IR sequence while T1-weighted spin echo was done following a standard sequence. Gadopentetate dimeglumine (Magnevist, Berlex, Montville, NJ) was administered at 0.1 mmol/kg of body weight. The authors focused on the following imaging hallmarks:
- Signal intensities based on analysis of tumor, white matter, gray matter, and cerebral spinal fluid
- Contrast-to-enhancement ratio
- Contrast ratio of tumor to white matter
In total, 352 metastases were found in 31 patients. Noncontrast T1-weighted SE MRI revealed 162 lesions while contrast-enhanced imaging showed 350. In comparison, precontrast T1-weighted IR MRI found 94 lesions while postcontrast imaging highlighted 233.
On the unenhanced images, the T1-weighted SE sequence was better at pinpointing hyperintense lesions, while the T1-weighted IR sequence was more adept with hypointense metastases, the group reported. On the contrast-enhanced imagines, T1-weighted SE MRI revealed 119 more metastases in 15 patients than the second protocol.
Both contrast-enhanced sequences were able to detect metastases larger than 10 mm with similar enhancing tumor volumes. However, T1-weighted spin echo detected more metastases that were smaller than 5 mm. T1-weighted inversion recovery was not suitable for finding small metastases, although performance was improved with a contrast medium, the authors stated.
T1-weighted inversion recovery fared better for demonstrating an increase in tumor signal intensity and a higher contrast ratio of tumor to cerebral spinal fluid. However, there was no significant difference in the contrast-to-enhancement ratio of metastases.
"Although pre-enhanced (T1-weighted IR) imaging is superior in revealing hypointense lesions, pre-enhanced (T1-weighted SE) can detect more brain metastases because of its sensitivity to bleeding lesions," the authors wrote. "Our results ... suggest that (T1-weighted SE) ... should be used ... in detecting brain metastases at 1.5T" (American Journal of Neuroradiology, January 9, 2008).
The group suggested that higher doses of contrast medium could improve T1-weighted inversion-recovery imaging results, but acknowledged that a double or single dose would be outside the norms of clinical practice.
By Shalmali Pal
AuntMinnie.com staff writer
February 27, 2008
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