Transcranial Dopplersonography of the vertebro-basilar system

Effects of Student-Performed Point-of-Care Ultrasound on Physician Diagnosis and Management of Patients in the Emergency Department

BACKGROUND

Despite the increasing integration of ultrasound training into medical education, there is an inadequate body of research demonstrating the benefits and practicality of medical student-performed point-of-care ultrasound (SP-POCUS) in the clinical setting.

OBJECTIVES

The primary purpose of this study was to evaluate the effects that SP-POCUS can have on physician diagnosis and management of patients in the emergency department, with a secondary purpose of evaluating the diagnostic accuracy of SP-POCUS.

METHODS

SP-POCUS examinations were performed in the emergency department by medical students who completed year one of a 4-year medical school curriculum with integrated ultrasound training. Scans were evaluated by an emergency physician who then completed a survey to record any changes in diagnosis and management.

RESULTS

A total of 641 scans were performed on the 482 patients enrolled in this study. SP-POCUS resulted in a change in management in 17.3% of scans performed. For 12.4% of scans, SP-POCUS discovered a new diagnosis. SP-POCUS reduced time to disposition 33.5% of the time. Because of SP-POCUS, physicians avoided ordering an additional imaging study for 53.0% of the scans performed. There was 94.7% physician agreement with SP-POCUS diagnosis.

CONCLUSIONS

This study showed that SP-POCUS is feasible and may potentially have a meaningful impact on physician diagnosis and management of patients in the emergency department. In addition, the implementation of SP-POCUS could serve as an ideal method of developing ultrasound skills in medical school while positively impacting patient care.

Latin American consensus on the use of transcranial Doppler in the diagnosis of brain death

Transcranial Doppler evaluates cerebral hemodynamics in patients with brain injury and is a useful technical tool in diagnosing cerebral circulatory arrest, usually present in the brain-dead patient. This Latin American Consensus was formed by a group of 26 physicians experienced in the use of transcranial Doppler in the context of brain death. The purpose of this agreement was to make recommendations regarding the indications, technique, and interpretation of the study of transcranial ultrasonography in patients with a clinical diagnosis of brain death or in the patient whose clinical diagnosis presents difficulties; a working group was formed to enable further knowledge and to strengthen ties between Latin American physicians working on the same topic. A review of the literature, concepts,and experiences were exchanged in two meetings and via the Internet. Questions about pathophysiology, equipment, techniques, findings, common problems, and the interpretation of transcranial Doppler in the context of brain death were answered. The basic consensus statements are the following: cerebral circulatory arrest is the final stage in the evolution of progressive intracranial hypertension, which is visualized with transcranial Doppler as a "pattern of cerebral circulatory arrest". The following are accepted as the standard of cerebral circulatory arrest: reverberant pattern, systolic spikes, and absence of previously demonstrated flow. Ultrasonography should be used - in acceptable hemodynamic conditions - in the anterior circulation bilaterally (middle cerebral artery) and in the posterior (basilar artery) territory. If no ultrasonographic images are found in any or all of these vessels, their proximal arteries are acceptable to be studied to look for a a pattern of cerebral circulatory arrest.

Fabrication of a PMN-PT single crystal-based transcranial Doppler transducer and the power regulation of its detection system

Doppler sonographic measurement of flow velocity in the basal cerebral arteries through the intact skull was developed using a pulsed Doppler technique and 2 MHz emitting frequency. Relaxor-based ferroelectric single crystals Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ (PMN-PT) were chosen to be the piezoelectric transducer material due to their ultrahigh piezoelectric coefficients, high electromechanical coupling coefficients and low dielectric loss. The pulse-echo response of the transducer was measured using the conventional pulse-echo method in a water bath at room temperature. The −6 dB bandwidth of the transducer is 68.4% and the sensitivity is −17.4 dB. In order to get a good match between transducer and detection system, different transmission powers have been regulated by changing the impedance of the transmitting electric circuit. In the middle cerebral artery (MCA) measurement photograph results, as the transmission power is increasing, the detection results become clearer and clearer. A comparison at the same transmission power for different transducers shows that the detection photograph obtained by the crystal transducer was clearer than that obtained with a commercial transducer, which should make it easier for doctors to find the cerebral arteries.

Changes of blood flow velocity indicating mechanical compression of the vertebral arteries during rotation of the head in the normal human measured with transcranial Doppler sonography

The dynamical changes of blood flow velocity of the intracranial vertebral arteries (VA's) and proximal basilar artery (BA) provoked by rotation of the head in normal volunteers were measured using pulsed-wave transcranial Doppler sonography (TCD). In another group both VA's were examined simultaneously with 2-channel TCD. Blood flow velocities diminished compared to the neutral position in all vessels, independently of the side. Total obstruction of the flow was not observed. Our findings reveal a definitive decrease of blood flow velocity at the vertebrobasilar artery system provoked by rotation of the head in normal humans. This physiological phenomenon is suggested to have an impact on the cerebral blood flow in patients with impaired autoregulation of the cerebral vessels, low volume flow reserve in the contralateral VA or insufficient collateral channels because of normal anatomical variation, especially those patients under general anesthesia or comatose.

The transcranial Doppler standardization project. Phase 1 results. The TCD Study Group, American Society of Neuroimaging

A project to pursue standardization of the performance and interpretation of transcranial Doppler studies was designed. Phase I consisted of a national survey of the current practice of transcranial Doppler in the United States. From 200 ultrasound laboratories surveyed about the use of transcranial Doppler, 60 completed questionnaires were returned. The results show that further standardization of transcranial Doppler performance and interpretation is necessary, and provide the foundation for phases II and III of the project.

Transcranial doppler findings during spontaneous recanalization of vertebrobasilar occlusions

Transcranial Doppler sonography (TCD) is of recognized value in the noninvasive detection of intracranial stenosis and occlusion. Serial TCD studies can detect recanalization of middle cerebral artery occlusion. Little information exists on TCD findings during vertebrobasilar recanalization. We report a 25-year-old woman with chronic meningitis who developed severe pontine and cerebellar infarctions due to bilateral distal vertebral and proximal basilar artery occlusion. Initial TCD showed a high-resistance signal from the distal right vertebral artery and no signal from the basilar artery. Evolutionary changes in flow velocities detected by seven TCD studies over a 5-week period suggested spontaneous recanalization of the distal vertebral and proximal basilar artery occlusion. These findings were accompanied by dramatic clinical improvement. Recurrent symptoms and TCD on day 73 suggested reocclusion, confirmed by repeat angiography. TCD may be useful for monitoring posterior circulation hemodynamics during recanalization of vertebrobasilar occlusions in selected patients.

Imaging of the intracranial vertebrobasilar system using color-coded ultrasound

BACKGROUND

Anatomic variety and difficult accessibility of the vertebrobasilar arteries pose considerable problems to conventional ultrasound. We evaluated the diagnostic potential of transcranial color-coded sonography in the distal part of this system.

METHODS

We insonated the intracranial section of the vertebrobasilar arteries through the foramen magnum window in 24 healthy individuals using a Doppler color flow imaging system in connection with a 2.5-MHz sector transducer. Magnetic resonance images in special inclination planes were performed and compared with the color-coded duplex images in five cases.

RESULTS

The B-mode image of the craniocervical junction and the intracranial parenchymal structures in addition to the color-coded blood flow allowed an unambiguous identification of the vertebrobasilar arteries (vertebral artery, 96%; basilar artery, 79%; and posterior inferior cerebellar artery, 50%). Blood flow velocities were measured considering the insonation angles: vertebral arteries, 50/24 cm/sec (30 degrees); basilar artery, 59/28 cm/sec (4 degrees); and posterior inferior cerebellar artery, 56/30 cm/sec (20 degrees) [peak systolic/end diastolic blood flow velocity (mean angle correction)].

CONCLUSIONS

Transcranial color-coded sonography enables accurate identification and differentiation of the intracranial vertebrobasilar arteries and improves accuracy of Doppler measurements. It may prove useful for evaluation of tortuosity and for hemodynamic studies in this vascular territory.

Evaluation of the vertebrobasilar-posterior system by transcranial color duplex sonography in adults

BACKGROUND AND PURPOSE

The transcranial color duplex sonography technique was applied to the vertebrobasilar-posterior system to provide normal data for clinical application.

METHODS

The intracranial posterior circulation was studied in 49 healthy volunteers (mean +/- SD age, 35 +/- 12 years) by a transcranial and suboccipital approach with a 2.0-MHz sector transducer of a computed sonography system.

RESULTS

The posterior cerebral artery and the vertebrobasilar system were depicted clearly in the color Doppler mode. Pulsed Doppler signals could be recorded in the posterior cerebral (100%), basilar (92%), and vertebral arteries (89%). The following normal values were provided for all vessels: systolic peak, end-diastolic maximum, time-averaged, and time-averaged maximum velocities; resistance and pulsatility indexes; and a spectral broadening index. Mean +/- SD values were 45.9 +/- 9.6, 45.5 +/- 10.8, and 39.2 +/- 10.6 cm/sec for time-averaged maximum velocity, and 28.3 +/- 6.5, 30.6 +/- 7.2, and 24.7 +/- 8.4 cm/sec for time-averaged velocity in the posterior cerebral, basilar, and vertebral arteries, respectively. In a reproducibility study, duplex measurements of the posterior cerebral arteries were repeated in 27 subjects. The correlation between the two examiners was high (r = 0.56, p less than or equal to 0.0001 for time-averaged maximum velocity).

CONCLUSIONS

Color duplex sonography of the vertebrobasilar-posterior system is a new, noninvasive, bedside investigative technique. It permits visualization of artery flow in real time, relating these to adjacent brain and cranial structures, as well as angle-corrected duplex measurement of "true" flow velocities at defined sites of the vessels. Thus, it will open new diagnostic possibilities in disorders of the posterior circulation.