Usefulness of contrast-enhanced T1-weighted sampling perfection with application-optimized contrasts by using different flip angle evolutions in detection of small brain metastasis at 3T MR imaging: comparison with magnetization-prepared rapid acquisition of gradient echo imaging

Abstract

Background and purpose: Early accurate diagnosis of brain metastases is crucial for a patient's prognosis. This study aimed to compare the conspicuity and detectability of small brain metastases between contrast-enhanced 3D fast spin-echo (sampling perfection with application-optimized contrasts by using different flip angle evolutions [SPACE]) and 3D gradient-echo (GE) T1-weighted (magnetization-prepared rapid acquisition of GE [MPRAGE]) images at 3T.

Materials and methods: Sixty-nine consecutive patients with suspected brain metastases were evaluated prospectively by using SPACE and MPRAGE on a 3T MR imaging system. After careful evaluation by 2 experienced neuroradiologists, 92 lesions from 16 patients were selected as brain metastases. We compared the shorter diameter, contrast rate (CR), and contrast-to-noise ratio (CNR) of each lesion. Diagnostic ability was compared by using receiver operating characteristic (ROC) analysis. Ten radiologists (5 neuroradiologists and 5 residents) participated in the reading.

Results: The mean diameter was significantly larger by using SPACE than MPRAGE (mean, 4.5 +/- 3.7 versus 4.3 +/- 3.7 mm, P = .0014). The CR and CNR of SPACE (mean, 57.3 +/- 47.4%, 3.0 +/- 1.9, respectively) were significantly higher than those of MPRAGE (mean, 37.9 +/- 41.2%, 2.6 +/- 2.2; P < .0001, P = .04). The mean area under the ROC curve was significantly larger with SPACE than with MPRAGE (neuroradiologists, 0.99 versus 0.88, P = .013; residents, 0.99 versus 0.78, P = .0001).

Conclusions: Lesion detectability was significantly higher on SPACE than on MPRAGE, irrespective of the experience of the reader in neuroradiology. SPACE should be a promising diagnostic technique for assessing brain metastases.

Fig 1.

A case with brain metastases depicted clearly on SPACE. A, Sagittal image of contrast-enhanced SPACE. B, Sagittal image of contrast-enhanced MPRAGE. The anatomic levels of these images conform. The SPACE image shows numerous small enhancing lesions, whereas only a few lesions with subtle enhancement are barely visible on MPRAGE image. Arrows indicate lesions delineated only on SPACE.

Fig 2.

Definition of the regions of interest. A, Contrast-enhanced sagittal SPACE image. B, Contrast-enhanced sagittal MPRAGE image. A circular or oval region of interest for a lesion is as large as possible, excluding lesion edges, to avoid a partial volume effect (solid oval), and the region of interest for the background is on the brain parenchyma near the lesion in the same plane (dotted circle). We defined these regions of interest carefully to avoid CSF or vessels. The size and shape of the region of interest on the brain parenchyma are identical on both SPACE and MPRAGE images.

Fig 3.

Results of the ROC analyses. In both observer groups, the Az was significantly higher for SPACE than for MPRAGE. The difference in Az values between the 2 observer groups was smaller for SPACE images. The asterisk in A indicates residents, P = .0001; the dagger in B, neuroradiologists, P = .0013.

Fig 4.

The contrast-enhanced SPACE image (A) clearly reveals an enhancing nodular lesion (arrow), whereas the lesion shows faint enhancement on the contrast-enhanced MPRAGE (B) and is barely visible. This lesion was noted by 9 observers on SPACE, but overlooked by 8 readers on MPRAGE.