Whole-body DWI outperforms established modalities for lung cancer staging

May 22, 2007

Whole-body diffusion-weighted MRI has been introduced to complement and possibly compete against whole-body FDG PET and whole-body anatomical MRI for staging cancer metastasis.

Whole-body diffusion-weighted MRI has been introduced to complement and possibly compete against whole-body FDG PET and whole-body anatomical MRI for staging cancer metastasis.

The new concept, which has been the subject of several scientific papers at the meeting, outperformed FDG-PET and was significantly more accurate than whole-body MRI for M-staging of lung cancer.

Speaking for his colleagues at Kobe University Graduate School of Medicine in Japan, Dr. Yoshiharu Ohno presented the first prospective clinical trial comparing the accuracy of the three approaches to lung cancer staging. Ohno is director of functional and diagnostic imaging research.

Subjects were 74 consecutive patients with confirmed lung cancers: 47 cases of adenocarcinoma, 13 of squamous cell carcinoma, and seven each of small- and large-cell cancer. With per-patient sensitivity and specificity rates of 85.7% and 90% respectively, whole-body diffusion-weighted MRI was more accurate than FDG PET, which had sensitivity and specificity rates of 85.7% and 81.6%, respectively. Whole-body MRI without diffusion-weighted imaging had 71.4% sensitivity and 85% specificity rates. The trial did not test FDG PET/CT, which has repeatedly outperformed PET alone for whole-body cancer staging. Fourteen patients had stage IV disease. Staging accuracy was confirmed with follow-up call a year later.

Findings of metastases were based on a radiologist's assessment using a five-point visual system to score each approach for each patient. The abstract did not mention who read the scans or whether the readers were blinded to previous results. A per-lesion analysis was not performed. Interobserver agreement was substantial, Ohno said.

Contrast-enhanced whole-body MRI was performed on a 1.5T Philips Intera scanner. The same device also served as a platform for nonenhanced whole-body MRI. Short T1 inversion-recovery turbo spin echo and dual-phase T1-weighted gradient echo imaging were used for the anatomic workup. Scan parameters for whole-body diffusion-weighted imaging included a 265 x 530-mm field of view, 128 x 256-pixel matrix, and 8-mm slice thicknesses with 1-mm slice gaps. Whole-body FDG PET was performed on a Philips Allegro using a standard whole-body protocol.

In the receiver operating characteristic (ROC) analysis of staging accuracy, whole-body diffusion-weighted imaging staging was assigned a kappa value of 0.61, which occupied considerably less area under the curve than whole-body MRI alone (0.52) or PET (0.57).

The addition of diffusion-weighted data will help radiologists read whole-body MRI fast and help compensate for the low specificity of MRI alone, Ohno said in an interview.

"First, I recommend to my colleagues to check the whole-body diffusion-weighted images for high signal intensities. After that, they should read through their whole-body MRI with contrast enhancement. Detection is best with whole-body MRI and diffusion-weighted imaging, but it is not good for initial diagnosis," he said.

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