Diagnostic value of three-dimensional transcranial contrast duplex sonography

Investigation of 3D vessel reconstruction under Doppler imaging with phantoms: Towards reconstruction of the Circle of Willis

BACKGROUND

Stroke is the second leading cause of death across the globe. Early screening and risk detection could provide early intervention and possibly prevent its incidence. Imaging modalities, including 1D-Transcranial Doppler Ultrasound (1D-TCD) or Transcranial Color-code sonography (TCCS), could only provide low spatial resolution or 2D image information, respectively. Notably, 3D imaging modalities including CT have high radiation exposure, whereas MRI is expensive and cannot be adopted in patients with implanted devices. This study proposes an alternative imaging solution for reconstructing 3D Doppler ultrasound geared towards providing a screening tool for the 3D vessel structure of the brain.

METHODS

The system comprises an ultrasound phased array attached to a servo motor, which can rotate 180˚ at a speed of 2˚/s. We extracted the color Doppler ROI from the image before reconstructing it into a 3D view using a customized pixel-based algorithm. Different vascular diameters, flow velocity, and depth were tested using a vascular phantom with a pumped flow to confirm the system for imaging blood flow. These variables were set to mimic the vessel diameter, flow speed, and depth of the Circle of Willis (CoW) during a transcranial screening.

RESULTS AND CONCLUSIONS

The lower values of absolute error and ratio were found in the larger vascular channels, and vessel diameter overrepresentation was observed. Under different flow velocities, such diameter overrepresentation in the reconstructed flow did not change much; however, it did change with different depths. Meanwhile, the setting of the velocity scale and the color gain affected the dimension of reconstructed objectives. Moreover, we presented a 3D image of CoW from a subject to demonstrate its potential. The findings of this work can provide a good reference for further studies on the reconstruction of the CoW or other blood vessels using Doppler imaging.

Intracranial collateral pathways assessed by contrast-enhanced three-dimensional transcranial color-coded sonography

Individual parameter settings of the duplex machine and limited insonation angles may influence the visualization of small intracranial vessels in 2-D transcranial color-coded sonography. The aim of our study was the morphologic assessment of intracranial collateral pathways (first auditory area celiac artery, A(1)CA; anterior communicating artery, AComA; first parental generation celiac artery P(1)CA; posterior communicating artery, PComA) using 3-D transcranial color-coded duplex sonography (3-D TCCS) and digital subtraction angiography (DSA). A total of 41 patients with large vessel disease and 30 patients who had suffered subarachnoidal hemorrhage (mean age 52 +/- 15 years) were involved. In all patients, angiography was performed within 10 days following 3-D sonography. The patients were investigated with a color-coded duplex system using the power mode. Contrast enhancement was achieved by continuous infusion of a galactose-based echo-enhancer using a perfusor pump. The 3-D system consists of an electromagnet that induces a low-intensity magnetic field near the head of the patient. A magnetic position sensor is attached to the ultrasound (US) probe and transmits the spatial orientation to a personal computer, which also receives the corresponding 2-D images from the video port of the duplex machine. Angiography revealed a "complete" circle of Willis in one third of the patients and, in the remaining patients at least one vessel was hypoplastic or absent. Sufficient temporal bone windows allowed the sonographic investigation of 466 (94%) of 497 expected arterial segments. The comparison of both techniques resulted in a weighted kappa value of 0.56 for the A(1)CA and 0.63 for the AComA. In the posterior circulation kappa values of 0.56 for the P(1)CA and 0.43 for the PComA were calculated. In 50 vessels (10%), 3-D sonography misdiagnosed the diameter of a collateral vessel as normal and angiography revealed hypoplasia or aplasia of this vessel. The main advantage of 3-D TCCS is that it enables the investigator to reconstruct virtually any arbitrary view angle. Compared with angiography or magnetic resonance (MR) angiography, 3-D sonography can be performed easily in critically ill patients on stroke units or intensive care units. The noninvasive assessment of the circle of Willis may be useful in patients who undergo carotid surgery without angiography. Combined with hemodynamic information, contrast-enhanced 3-D TCCS might increase the diagnostic impact of transcranial US.

Three-dimensional intraoperative ultrasound of vascular malformations and supratentorial tumors

The benefits and limits of a magnetic sensor-based 3-dimensional (3D) intraoperative ultrasound technique during surgery of vascular malformations and supratentorial tumors were evaluated. Twenty patients with 11 vascular malformations and 9 supratentorial tumors undergoing microsurgical resection or clipping were investigated with an interactive magnetic sensor data acquisition system allowing freehand scanning. An ultrasound probe with a mounted sensor was used after craniotomies to localize lesions, outline tumors or malformation margins, and identify supplying vessels. A 3D data set was obtained allowing reformation of multiple slices in all 3 planes and comparison to 2-dimensional (2D) intraoperative ultrasound images. Off-line gray-scale segmentation analysis allowed differentiation between tissue with different echogenicities. Color-coded information about blood flow was extracted from the images with a reconstruction algorithm. This allowed photorealistic surface displays of perfused tissue, tumor, and surrounding vessels. Three-dimensional intraoperative ultrasound data acquisition was obtained within 5 minutes. Off-line analysis and reconstruction time depends on the type of imaging display and can take up to 30 minutes. The spatial relation between aneurysm sac and surrounding vessels or the skull base could be enhanced in 3 out of 6 aneurysms with 3D intraoperative ultrasound. Perforating arteries were visible in 3 cases only by using 3D imaging. 3D ultrasound provides a promising imaging technique, offering the neurosurgeon an intraoperative spatial orientation of the lesion and its vascular relationships. Thereby, it may improve safety of surgery and understanding of 2D ultrasound images.

Use of transcranial duplex sonography in the treatment of intracranial aneurysms

The use of transcranial duplex sonography in documenting additional findings by measuring vasospasm and visualising aneurysms in neurosurgical patients is described. Daily measurement of vasospasm using this method enables reassessment of the status of the lesion in the context of the patient's clinical condition. This offers a practical alternative to angiographic investigation in aneurysm patients, provided ultrasound penetration of the cranium is optimal.

New ultrasound techniques and their application in neurosurgical intra-operative sonography

We describe a variety of new ultrasound techniques by their physical background, potentials and applications regarding usefulness during intra-operative neurosurgical procedures. Transducers like high-frequency and small rotating probes fitting into neuroendoscopes, imaging techniques as extended field-of-view technique, harmonic imaging, echo-enhancers, 3-D imaging and the real-time integration of neurosonography with pre-operative CT- or MR-data are mentioned. The technical or physical principles are explained, followed by a discussion of these techniques from available literature dealing with their intra-operative neurosurgical applications and the experience of the authors with the techniques. With higher frequencies micromillimeter imaging is possible and small probe allows endoneurosonography. Echo-enhancers and harmonic imaging improve the signal-to-noise ratio and 3-D imaging and extended field-of-view techniques allows a better understanding of the pathoanatomy. With the real-time integration of intra-operative ultrasound images and pre-operative CT or MR images additional information, like hemodynamic pattern, are available for the neurosurgeon. Although until now only a limited number of reports about new sonographic techniques during intra-operative application in neurosurgery exist, the methods seem to be promising in creating images easier to understand, incorporating more information about pathoanatomy and supplying the neurosurgeon with information additional to that provided by CT and MRI.

Sonographic parenchymal and brain perfusion imaging: preliminary results in four patients following decompressive surgery for malignant middle cerebral artery infarct

To investigate new methods of diagnostic transcranial sonography for brain parenchymal, vascular and perfusion imaging, we performed 3-D native tissue harmonic transcranial sonography (3D-nthTCS), 3-D transcranial color-coded duplex sonography (3D-TCCS), and "loss-of-correlation" imaging (LOC-TCCS) in four patients following early hemicraniectomy due to space-occupying "malignant" middle cerebral artery infarction (MMCAI). Three-dimensional datasets, utilizing 3D-nthTCS and 3D-TCCS, were created and up to 10 axial 2-D B-mode image planes, similar to CCT, reconstructed in each patient. Three-dimensional reconstructions of the circle of Willis documented one persistent carotid-T occlusion and three recanalizations of the MCA. LOC-TCCS, based on stimulated acoustic emission from an ultrasound (US) contrast agent, demonstrated a perfusion deficit in 2 of 3 patients, with regard to their infarcts. Concluding, 3D-nthTCS, 3D-TCCS and LOC-TCCS are promising tools for bedside monitoring, early prognosis and treatment evaluation for MMCAI in the postoperative period. Further studies should be performed to standardize these new methods and evaluate their applications through the intact calvarina.

Three-dimensional transcranial colour-coded duplex sonography of the transverse sinus

The case of a patient with partial superior sagittal sinus and partial right sided transverse sinus thrombosis, and posterior fossa venous collaterals is presented. We report on the use of venous transcranial colour-coded duplex sonography (TCCS), combined with a new three-dimensional transcranial duplex data acquisition system, which allows free hand scanning of the region of interest. TCCS with three-dimensional image reconstruction allowed a more precise spatial localization of venous flow signals in the posterior fossa and facilitated the understanding of the haemodynamics of the venous collateral network.

Three-dimensional transcranial color-coded sonography for the examination of the arteries of the circle of Willis

Because examinations of the intracranial vessels using conventional transcranial color-coded sonography (TCCS) lack spatial orientation and reproducibility, development of a three-dimensional (3-D) imaging technique is required. Three patients with middle cerebral artery (MCA) stenosis, three with suspected intracranial aneurysm, two with vascular malformation, and one healthy volunteer were investigated by 3-D TCCS using a magnetic spatial positioning sensor mounted on the transducer for simultaneous recording of the probe coordinates to create a volumetric data set. Three-dimensional transcranial color-coded sonography enabled good visualization of intracranial aneurysms and MCA stenoses. However, it failed to detect morphological details in vascular malformations. In conclusion, 3-D TCCS is a promising technique that opens new perspectives in depicting intracranial vessels and provides volume measurement of intracranial aneurysms.

Three-dimensional transcranial color-coded sonography of cerebral aneurysms

BACKGROUND AND PURPOSE

The role of 2-dimensional transcranial color-coded sonography (2D-TCCS) as a diagnostic tool in cases of vascular alteration is unquestioned. The skill of the operator, however, may be responsible for some intertrial variability. The clinical value of a new, workstation-based, 3D reconstruction system for TCCS was evaluated in patients with intracranial aneurysms.

METHODS

Thirty patients with 30 intracranial aneurysms were investigated (8 men, 22 women; mean+/-SD age 54+/-17 years). The TCCS examinations were performed with a 2-MHz probe using the power mode. The 3D system (3D-Echotech, Germany) consisted of an electromagnet, which induced a low-intensity magnetic field near the head of the patient. A magnetic position sensor was attached to the ultrasound probe and transmitted the spatial orientation of the probe to a workstation, which also received the corresponding 2D-images from the video-port of the duplex machine. The echo contrast enhancer D-galactose (Levovist, Schering, Germany) was used in all patients to improve the signal-to-noise ratio. All patients underwent presurgical digital subtraction angiography (DSA) to demonstrate the aneurysm.

RESULTS

Twenty-nine of 30 angiographically proven intracranial aneurysms (97%) were detected by 3D-TCCS. The aneurysmal diameter estimated by DSA ranged from 3 to 16 mm (mean 7. 2+/-3.6 mm). A comparison of the 3 main diameters of each aneurysm revealed a correlation coefficient of 0.95 between DSA and 3D-TCCS. The 3D determination of the aneurysmal size by 2 experienced sonographers correlated with 0.96.

CONCLUSIONS

3D-TCCS is a new, noninvasive method to investigate intracranial aneurysms. The differentiation between artifacts and true changes of the vessel anatomy is much easier in 3D-TCCS than in conventional 2D-TCCS. The new method yields an excellent correlation with the gold standard, DSA. Because the same 3D-TCCS data can be postprocessed by different investigators, it may be possible to improve reproducibility and increase the objectivity of transcranial color-coded duplex sonography.

Development and applications of 4-D ultrasound (dynamic 3-D) in neurosonology

The development and application of color-coded data in three-dimensional (3-D) reconstruction or four-dimensional (4-D) imaging (equal to dynamic 3-D) are demonstrated. In 4-D imaging, electrocardiography-triggered data acquisition of consecutive phases during the heart cycle are stored to form a multiphase 3-D data set. The option of color-coded data gives a new insight into such hemodynamic information. In the past, 3-D reconstructions were simple unicolor images, as in power mode, and the color-coded hemodynamic information was lost. These new options are presented here, along with color-coded data in examples of angiographically controlled pathologic results in extracranial and intracranial vessels.

Effect of echo contrast media on the visualization of transverse sinus thrombosis with transcranial 3-D duplex sonography

Transcranial duplex sonography has the capacity of detecting venous flow as in the transverse sinus. During a 6-month period, 28 consecutive patients (mean age 55 y) with a clinically suspected diagnosis of cerebral sinus thrombosis were included in the study. All patients were examined using 3-D ultrasound equipment within 24 h of having undergone either venous computerized tomography (CT), venous magnetic resonance imaging (MRI) or cerebral angiography. A total of 22 healthy patients had a normal venous CT, venous MRI or cerebral angiography of both transverse sinuses. Before echo contrast enhancement, the transverse sinus could be visualized in only 2 of these 44 sinuses (22 patients). A total of 6 patients with an unilaterally missed transverse sinus in 3-D ultrasound suffered from sinus thrombosis (n = 3), hypoplasia (n = 2) or aplasia (n = 1) of the unilateral transverse sinus in neuroradiological tests. In none of the patients with an thrombosis of the transverse sinus did ultrasound contrast media application improve the visualization of the affected sinus. Our study confirms that the normal transverse sinus, insonated through the contralateral temporal bone, often cannot be visualized without the use of contrast agents. With transcranial 3-D duplex sonography, a differentiation between thrombosis, hypoplasia and aplasia of the sinus was not possible.

3-D power Doppler cerebral angiography in neonates and young infants: comparison with 2-D power Doppler angiography

The aims of this study were to evaluate the ability of 3-dimensional (3-D) power Doppler angiography (3DPDA) to depict the intracranial vasculature in infants, to compare with 2-D power Doppler ultrasonography (2DPDU), and to explore the potential clinical applications of this procedure in young infants with brain disorders. We performed 3DPDA in 27 infants. 2DPDU were completed in both sagittal and coronal directions in 12 of these patients. In the other 15, only right sagittal plane images were available for comparison. Using a grading system and with only vessels with more than half of the length demonstrated included for comparison, we compared the Doppler signals of major vessels. 3DPDA could have good visualization in more than 60% of the internal carotid artery, ophthalmic artery, pericallosal artery, callosomarginal artery, internal cerebral vein, vein of Galen, and straight sinus in the sagittal plane. 3DPDA also could have good demonstration in about 50% of basilar artery in coronal plane, and posterior communicating artery, posterior cerebral artery, and lenticulostriate artery in sagittal plane. 3DPDA was better than 2DPDU in demonstrating all the major intracranial vessels in different planes, except the anterior communicating artery. In the anterior communicating artery, neither can demonstrate more than 30%.

Three-dimensional ultrasound imaging

The objective of this article is to provide scientists, engineers and clinicians with an up-to-date overview on the current state of development in the area of three-dimensional ultrasound (3-DUS) and to serve as a reference for individuals who wish to learn more about 3-DUS imaging. The sections will review the state of the art with respect to 3-DUS imaging, methods of data acquisition, analysis and display approaches. Clinical sections summarize patient research study results to date with discussion of applications by organ system. The basic algorithms and approaches to visualization of 3-D and 4-D ultrasound data are reviewed, including issues related to interactivity and user interfaces. The implications of recent developments for future ultrasound imaging/visualization systems are considered. Ultimately, an improved understanding of ultrasound data offered by 3-DUS may make it easier for primary care physicians to understand complex patient anatomy. Tertiary care physicians specializing in ultrasound can further enhance the quality of patient care by using high-speed networks to review volume ultrasound data at specialization centers. Access to volume data and expertise at specialization centers affords more sophisticated analysis and review, further augmenting patient diagnosis and treatment.

Echo contrast-enhanced three-dimensional power Doppler of intracranial arteries

The purpose of this study was to evaluate the potential of contrast-enhanced three-dimensional (3-D) power Doppler (CE3DPD) in the assessment of intracranial vascular structures, and to compare the results with unenhanced 3-D power Doppler (3DPD) and magnetic resonance angiography (MRA) findings. We insonated 25 patients without cerebrovascular diseases through the temporal bone window using 3DPD and CE3DPD; for comparison, 13 patients underwent MRA. Identification rates of vascular segments and of small branches of intracranial vessels were evaluated by two independent investigators blinded to MRA results. In 21 patients with adequate insonation conditions, CE3DPD significantly improved identification rates compared to 3DPD for the complete visualization of the P1 segment (80.9 vs. 19.0%, p < 0.005, P2 segment (80.9 vs. 42.8%, p < 0.05 and A1 segment (85.7 vs. 38.1%, p < 0.005). Furthermore, CE3DPD depicted, in significantly more examinations, branches of the middle (MCA) and posterior cerebral artery (PCA). Interobserver agreement was higher than 95% for the main intracranial segments and branches of the MCA, but relatively low (80.1-85.7%) for branches of the PCA. In comparison to CE3DPD, MRA identified only parieto-occipital branches of the PCA, temporal branches of the MCA, frontal branches of the anterior cerebral artery and the MCA bifurcation more frequently and accurately. In 4 patients with inadequate acoustic temporal bone windows, the application of a galactose-based microbubble suspension allowed clear 3-D visualization of almost all major intracranial vascular segments and some branches of the large arteries. In conclusion, CE3DPD is a more sensitive ultrasonic tool compared to unenhanced 3-D reconstructions. It makes 3-D ultrasound imaging of the basal cerebral circulation easier to perform and interpret, by providing an improved spatially oriented display of image position. As such, this method may increase operator diagnostic confidence level under pathologic conditions.

Transcranial 3D B-mode imaging in a case of cerebral hemorrhage

The case of a patient with temporal lobe hemorrhage is presented. This is the first report of use of a new three-dimensional data acquisition system that entails free-hand scanning with three-dimensional transcranial duplex sonography. Three-dimensional image reconstruction reduced the spatial asymmetry inherent in oblique two-dimensional ultrasonography, making evaluation of the precise location, size, and anatomic relations of intracranial hemorrhage easier.

The latest in ultrasound: three-dimensional imaging. Part II

INTRODUCTION

The three-dimensional (3D) reconstruction of ultrasound images has become a widespread option in ultrasound equipment. Specific softwares have become available and 3D reconstruction feasible since the early 1990s, particularly since 1994.

POSSIBLE CLINICAL APPLICATIONS

Several clinical applications are feasible in all parenchymatous organs (mainly the liver and prostate), hollow viscera (e.g. the bladder and gallbladder), peripheral vessels (supra-aortic trunks and limb vessels) and central (the aorta and iliac arteries) or cerebral vessels. Moreover, tumoral vessels in parenchymatous organs can be reconstructed, and even the fetus in the uterine cavity, with excellent detailing. The recent introduction of echocontrast agents and second harmonic imaging has permitted to study normal and abnormal peripheral, central and parenchymatous vessels, with similar patterns to those obtained with digital angiography. The spatial relationships between the vascular structures of the liver, kidney and placenta were studied with 3D ultrasound angiograms. The applications of this new technique include the analysis of vascular anatomy and the potential assessment of organ perfusion. THE LATEST APPLICATIONS--INTRAVASCULAR STUDIES: Some catheters with an ultrasound transducer in the tip have been tested for intravascular studies. Just like conventional transducers, they provide two-dimensional (2D) images which are then postprocessed into longitudinal 3D or volume reconstructions. The former resemble angiographic images and can be viewed 3D rotating the image along its longitudinal axis. Volume images, which are more complex and slower to obtain, can be rotated on any spatial plane and provide rich detailing of the internal vascular lumen. The clinical importance of intravascular ultrasound with 3D volume reconstructions lies in the diagnosis of vascular conditions and the assessment and monitoring of intravascular interventional procedures--e.g. to detect inaccurate deployment of intravascular stents and endoluminal grafts during the maneuver. Three-dimensional reconstructions involve geometric data assembly and volumetric interpolation of a spatially related sequence of tomographic cross sections generated by an ultrasound catheter withdrawn at a constant rate through a vascular segment of interest, resulting in the display of a straight segment. Therefore particular care is needed and there are some useful hints to avoid mistakes.

CONCLUSIONS

Three dimensional reconstructions of B-mode and color Doppler images are no longer a work in progress and their clinical importance and possible applications are both established and ever-increasing. On the other hand, independent of the different types of energy used, also computed tomography and magnetic resonance 3D reconstructions are very useful from a clinical viewpoint and they have become an established routine technique for both these methods. It is very likely that 3D volume reconstructions in ultrasound will find numerous applications in the near future. They may help to increase the diagnostic confidence and to facilitate diagnosis, intraprocedure monitoring in interventional radiology and follow-up and also to reduce the number of invasive examinations with iodinated contrast agents. This could result in cutting the cost and duration of the most expensive examinations. New, although invasive, applications can be hypothesized for intravascular or intraluminal catheters with an ultrasound transducer inside.

Three-dimensional reconstruction of the power flow Doppler imaging of intracranial vascular structures in the neonate

Three-dimensional (3D) ultrasonography reconstructing from power flow Doppler imaging (PF) is able to image the 3D structures of the vascular systems. We tried to display the 3D images of intracranial vascular structures in 5 neonates with a portable data processor. Data acquisition was performed using PF through the anterior fontanel. We succeeded in reconstructing vivid 3D images of the anterior cerebral arteries (ACA), basilar artery (BA), internal carotid arteries (ICA), middle cerebral arteries (MCA), lenticulostriate arteries (LSA), internal cerebral vein (ICV), the vein of Galen (GV) and straight sinus (SS) in all subjects. The MCA could be displayed in only a proximal portion. The images of the LSAs were fainter than the other vessels. These problems are based on the character of PF; the flow signal, sampling from the small sized vessels and the perpendicular vessels to ultrasonic beam, is weak. The images of these vessels are fainter than other vessels. These limitations of PF performance directly influence the quality of the 3D images. The benefits and limitations of 3D ultrasonography system are discussed.