Transcranial sonography: integration into target volume definition for glioblastoma multiforme

A stereological study of MRI and the Cavalieri principle combined for diagnosis and monitoring of brain tumor volume

In this study, we aimed to describe the application of the Cavalieri principle for the assessment of tumor volume using MRI without an over-projection/estimation effect. For this purpose, the volume of a patient's brain and the brain tumor volume, or the volume of the former tumor region, were estimated preoperatively and postoperatively using a combination of the Cavalieri principle and MRI. The previously described formula was modified for MRI measurements to eliminate the over-estimation effects of imaging. The total brain and tumor volumes estimated using the MRI of a representative patient with glioblastoma multiforme were: preoperative, 1562.46 cm³ and 81.59 cm³, respectively; and postoperative, 1571.72 cm³ and 86.92 cm³, respectively. The mean time to count points for an estimation of brain and tumor volume (or the volume of the former tumor region) were 14 minutes and 3 minutes, respectively. The coefficients of the errors of the estimates for brain and tumor volume (former tumor volume, postoperative) measurements were: preoperative 0.01 and 0.02; and postoperative 0.01 and 0.03, respectively. Our results show that the combination of MRI and the Cavalieri principle can provide an unbiased, direct and assumption-free estimate of the regions of interest. Therefore, the presented method could be applied efficiently without any need for special software, additional equipment or personnel other than that required for routine MRI in daily use.

Optimizing localization accuracy in head and neck, and brain radiotherapy

The purpose of this study was to investigate the impact on localization of utilizing contrast-enhanced CT scans and the formal input of a radiologist in the planning process. 25 head and neck/brain patients had pre- and post-contrast CT scans in the treatment position. Radiotherapy treatment was planned on the unenhanced CT images as per standard practice. Retrospectively, their scans (unenhanced and enhanced) were re-contoured by two oncologists and a radiologist. These new contours were compared with the original unenhanced treatment contours and differences in contour volume, geographical isocentre position and tolerance coverage of the associated planning target volumes (PTVs) were evaluated using the original plans. The use of contrast enhanced CT data during localization by the oncologist shows little change in gross tumour volumes (GTVs) or PTVs, geographical position or tolerance coverage for the targets in the brain studied here. Larger changes in mean volume are seen for the head and neck cases alone. Changes are greater and statistically significant (p < 0.05, Wilcoxon signed rank test) for localization by the radiologist. Furthermore, when comparing the original PTV marked by the oncologist with a new PTV re-contoured by the oncologist, but based on a GTV marked-up by the radiologist, again statistically significant (p < 0.01) changes in percentage volume are noted. Intraoperator precision is good, percentage volume differences being of the order 3-6%. PTVs also show improved standard deviations compared with GTVs. Geographic shifts are generally within our departmental tolerance levels for daily patient setup. Comparing precision of unenhanced data with enhanced, mean percentage volume changes are smaller, but not statistically significant. The use of enhanced scan data for localization has little effect on size, geographical position or tolerance coverage of PTVs marked up by the oncologists in this study. However, more important is the input from a radiologist. Statistically significant differences due to mark-up on enhanced scans by the radiologist are shown. Furthermore, significant differences are also seen between PTVs based on oncologist-generated GTVs, and those based on radiologist-generated GTVs.

Second harmonic imaging: a new ultrasound technique to assess human brain tumour perfusion

BACKGROUND

Second harmonic imaging is a new ultrasound technique that allows evaluation of brain tissue perfusion after application of an ultrasound contrast agent.

OBJECTIVE

To evaluate the potential of this technique for the assessment of abnormal echo contrast characteristics of different brain tumours.

METHODS

27 patients with brain tumours were studied. These were divided into four groups: gliomas, WHO grade III-IV (n = 6); meningiomas (n = 9); metastases (n = 5); and others (n = 7). Patients were examined by second harmonic imaging in a transverse axial insonation plane using the transtemporal approach. Following intravenous administration of 4 g (400 mg/ml) of a galactose based echo contrast agent, 62 time triggered images (one image per 2.5 seconds) were recorded and analysed off-line. Time-intensity curves of two regions of interest (tumour tissue and healthy brain tissue), including peak intensity (PI) (dB), time to peak intensity (TP) (s), and positive gradient (PG) (dB/s), as well as ratios of the peak intensities of the two regions of interest, were derived from the data and compared intraindividually and interindividually.

RESULTS

After administration of the contrast agent a marked enhancement of echo contrast was visible in the tumour tissue in all patients. Mean PI and PG were significantly higher in tumour tissue than in healthy brain parenchyma (11.8 v 5.1 dB and 0.69 v 0.16 dB/s; p < 0.001). TP did not differ significantly (37.1 v 50.2 s; p = 0.14). A tendency towards higher PI and PG as well as shorter TP was apparent in malignant gliomas. When comparing different tumour types, however, none of these variables reached significance, nor were there significant differences between malignant and benign tumours in general.

CONCLUSIONS

Second harmonic imaging not only allows identification of brain tumours, but may also help in distinguishing between different tumour types. It gives additional and alternative information about tumour perfusion. Further studies are needed to evaluate the clinical potential of this technique in investigating brain tumours-for example in follow up investigations of patients undergoing radiation or chemotherapy-especially in comparison with neuroradiological and neuropathological findings.

Perspectives of B-mode transcranial ultrasound

Transcranial color coded sonography has proved valuable in the diagnostic work-up of cerebrovascular disorders in adults. More recently, evidences have converged that transcranial sonography is also useful in the diagnosis of brain parenchymal disorders. Here, a new field of application is the visualization of signal intensity shift in specific brain areas in some neurodegenerative disorders (Parkinson's disease, idiopathic dystonia, and depression). Findings obtained by transcranial ultrasound complement information from other neuroimaging data in these disorders and have led to the generation of new pathophysiological concepts. In this review we summarize the application fields of transcranial sonography with special emphasis on recent findings in neurodegenerative disorders and their implications for future research. As new application and processing techniques are being developed transcranial color coded sonography will gain increasing impact on both diagnosis and research of neurological disorders.