Computed measures on computed tomograms of the head

Transcranial Doppler in a Hispanic-Mestizo population with neurological diseases: a study of sonographic window and its determinants

Between 5% and 37% of patients are not suitable for transtemporal insonation with transcranial Doppler (TCD). This unsuitability is particularly frequent in elderly females and non-Caucasians. We aim to evaluate TCD efficiency in a mixed Hispanic population in Santiago, Chile and to determine whether factors associated with the presence of optimal windows depend exclusively on patient-related elements. Seven hundred forty-nine patients were evaluated with power mode TCD. Optimal temporal windows (TWs) included detection of the middle, anterior, posterior cerebral arteries and terminal carotid. The patient's age and sex, the location of the examination, the time of day, whether the test was conducted on weekends and whether mechanical ventilation was used were recorded. Percentages of optimal windows were calculated. Examinations were deemed ideal if both TWs were optimal. TWs were obtained in 82% of cases. In univariate analyses, male sex (P < 0.001), an age below 60 years (P < 0.0001) and mechanical ventilation (P= 0.04) correlated with ideal TWs. Using logistic regression where dependent variable was a non-ideal window only male sex odds ratio (OR) 2.3 (1.51-3.45) and age below 60 OR 13.8 (7.8-24.6) were statistically significant. Our findings indicate that Hispanic populations have detection rates for TWs similar to Europeans and are affected by patient-related elements.

Characterization of ultrasound propagation through ex-vivo human temporal bone

Adjuvant therapies that lower the thrombolytic dose or increase its efficacy would represent a significant breakthrough in the treatment of patients with ischemic stroke. The objective of this study was to perform intracranial measurements of the acoustic pressure field generated by 0.12, 1.03 and 2.00-MHz ultrasound transducers to identify optimal ultrasound parameters that would maximize penetration and minimize aberration of the beam. To achieve this goal, in vitro experiments were conducted on five human skull specimens. In a water-filled tank, two unfocused transducers (0.12 and 1.03 MHz) and one focused transducer (2.00 MHz) were consecutively placed near the right temporal bone of each skull. A hydrophone, mounted on a micropositioning system, was moved to an estimated location of the middle cerebral artery (MCA) origin, and measurements of the surrounding acoustic pressure field were performed. For each measurement, the distance from the position of maximum acoustic pressure to the estimated origin of the MCA inside the skulls was quantified. The -3 dB depth-of-field and beamwidth in the skull were also investigated as a function of the three frequencies. Results show that the transducer alignment relative to the skull is a significant determinant of the detailed behavior of the acoustic field inside the skull. For optimal penetration, insonation normal to the temporal bone was needed. The shape of the 0.12-MHz intracranial beam was more distorted than those at 1.03 and 2.00 MHz because of the large aperture and beamwidth. However, lower ultrasound pressure reduction was observed at 0.12 MHz (22.5%). At 1.03 and 2.00 MHz, two skulls had an insufficient temporal bone window and attenuated the beam severely (up to 96.6% pressure reduction). For all frequencies, constructive and destructive interference patterns were seen near the contralateral skull wall at various elevations. The 0.12-MHz ultrasound beam depth-of-field was affected the most when passing through the temporal bone and showed a decrease in size of more than 55% on average. The speed of sound in the temporal bone of each skull was estimated at 1.03 MHz and demonstrated a large range (1752.1 to 3285.3 m/s). Attenuation coefficients at 1.03 and 2.00 MHz were also derived for each of the five skull specimens. This work provides needed information on ultrasound beam shapes inside the human skull, which is a necessary first step for the development of an optimal transcranial ultrasound-enhanced thrombolysis device.

Rate of successful recording of blood flow signals in the middle cerebral artery using transcranial Doppler sonography

BACKGROUND AND PURPOSE

To assess the usefulness of transcranial Doppler sonography, we investigated the rate of blood flow signal recording failure in the middle cerebral artery in Japanese subjects. Furthermore, we studied the effect of increased emitted power on the rate of successful recording in some of the patients in whom recording failure had been detected at the standard transducer power of 100 mW/cm2.

METHODS

To evaluate the rate of successful recording, we measured blood flow signals in 597 patients (age range, 16 to 89 years) for screening of cerebrovascular disease by using a 2-MHz range-gated, pulsed-wave Doppler instrument at the standard transducer power. In 18 elderly patients with recording failure at the standard power, we assessed the effect of increased emitted power of 400 mW/cm2 on flow signal recording.

RESULTS

Blood flow signals were recorded in 920 (77.1%) of the 1194 middle cerebral arteries of the 597 patients studied. The rate of successful recording of bilateral middle cerebral artery flow signals (70.9%; 423 of 597 patients) decreased with age, especially in females (17.0% in women aged 70 years or older). In 12 of 18 elderly patients with recording failure at the standard power, blood flow signals could be detected at the increased emitted power of 400 mW/cm2.

CONCLUSIONS

The rate of successful recording of blood flow signals in Japanese subjects decreases with advancing age, especially in females. Increasing the emitted power markedly improves the successful recording rate.

Evaluation of cerebrovascular disease by combined extracranial and transcranial Doppler sonography. Experience in 1,039 patients

Results from 1,039 combined cervical and transcranial Doppler examinations are reported. Satisfactory transcranial signals were not found in 2.7% of the cases. Compared with angiography, the accuracy of transcranial criteria in assessing collateral flow over the circle of Willis was 94 and 88% for anterior and posterior circulation, respectively. The method also appeared very promising for detection of lesions of the intracranial arteries although the number of such cases with angiographic verification was limited in the present series. Arterial narrowing due to cerebral vasospasm was diagnosed with a sensitivity of 80%. In patients with ruptured intracranial aneurysms, an incidence of 93% arterial narrowing in basal cerebral arteries was found. Patients with subarachnoid hemorrhage and no aneurysm on angiography also showed arterial narrowing with an incidence of 56%. It was possible to monitor the time course and severity of cerebral vasospasm. Arteriovenous malformations were characterized by Doppler findings of high velocities and low pulsatilities. These lesions were diagnosed with an accuracy of 95%.