Mustapha R. Hatab

Cerebral blood flow and cranial magnetic resonance imaging in eclampsia and severe preeclampsia

Objective To measure cerebral blood flow in women with eclampsia and severe preeclampsia using phase-contrast magnetic resonance imaging (MRI). Methods Women with eclampsia and severe preeclampsia were studied and compared with normotensive cohorts. Magnetic resonance imaging studies were performed initially in hypertensive women after seizure treatment or prophylaxis was given. Magnetic resonance imaging flow measurements were made using a phase contrast velocity imaging technique in each middle and posterior cerebral artery. Conventional brain MRI and magnetic resonance angiography of the circle of Willis were performed at the time of flow measurement. Women with preeclampsia and eclampsia served as their own controls and were matched with normotensive cohorts. All of the hypertensive women were studied again 4–5 weeks postpartum. Paired t test analysis and an analysis of variance were performed. Considering a 20% minimum detectable difference in flow, the power was 0.80, 0.92, 0.86, and 0.96 for the left and right middle cerebral arteries and the left and right posterior cerebral arteries, respectively. Results All 28 women enrolled were studied initially within 24 hours of delivery or of their most recent seizure. There were no significant differences in blood flow in either the posterior or middle cerebral arteries in women with eclampsia or severe preeclampsia between the initial studies and those 4–5 weeks postpartum, or compared with their normal counterparts. No findings of vasospasm were seen. T2-weighted brain images were markedly abnormal in all eight women with eclampsia, mildly abnormal in two of ten with severe preeclampsia, and normal in all ten controls. Conclusions No flow changes were seen in the posterior or middle cerebral arteries of women with eclampsia and severe preeclampsia despite the presence of remarkable brain lesions in all women with eclampsia. These findings question the role of vasospasm and cerebral hypoperfusion, although a vasodilatory effect of magnesium could not be excluded.

Characteristics of an OSLD in the diagnostic energy range

PURPOSE Optically stimulated luminescence (OSL) dosimetry has been recently introduced in radiation therapy as a potential alternative to the thermoluminescent dosimeter (TLD) system. The aim of this study was to investigate the feasibility of using OSL point dosimeters in the energy range used in diagnostic imaging. METHODS NanoDot OSL dosimeters (OSLDs) were used in this study, which started with testing the homogeneity of a new packet of nanoDots. Reproducibility and the effect of optical treatment (bleaching) were then examined, followed by an investigation of the effect of accumulated dose on the OSLD indicated doses. OSLD linearity, angular dependence, and energy dependence were also studied. Furthermore, comparison with LiF:Mg,Ti TLD chips using standard CT dose phantoms at 80 and 120 kVp settings was performed. RESULTS Batch homogeneity showed a coefficient of variation of <5%. Single-irradiation measurements with bleaching after each OSL readout was found to be associated with a 3.3% reproducibility (one standard deviation measured with a 8 mGy test dose), and no systematic change in OSLDs sensitivity could be noted from measurement to measurement. In contrast, the multiple-irradiation readout without bleaching in between measurements was found to be associated with an uncertainty (using a 6 mGy test dose) that systematically increased with accumulated dose, reaching 42% at 82 mGy. Good linearity was shown by nanoDots under general x-ray, CT, and mammography units with an R2 > 0.99. The angular dependence test showed a drop of approximately 70% in the OSLD response at 90 degrees in mammography (25 kVp). With the general radiography unit, the maximum drop was 40% at 80 kVp and 20% at 120 kVp, and it was only 10% with CT at both 80 and 120 kVp. The energy dependence study showed a range of ion chamber-to-OSLDs ratios between 0.81 and 1.56, at the energies investigated (29-62 keV). A paired t-test for comparing the OSLDs and TLDs showed no significant variation (p > 0.1). CONCLUSIONS OSLDs exhibited good batch homogeneity (<5%) and reproducibility (3.3%), as well as a linear response. In addition, they showed no statistically significant difference with TLDs in CT measurements (p > 0.1). However, high uncertainty (42%) in the dose estimate was found as a result of relatively high accumulated dose. Furthermore, nanoDots showed high angular dependence (up to 70%) in low kVp techniques. Energy dependence of about 60% was found, and correction factors were suggested for the range of energies investigated. Therefore, if angular and energy dependences are taken into consideration and the uncertainty associated with accumulated dose is avoided, OSLDs (nanoDots) can be suitable for use as point dosimeters in diagnostic settings.

Pediatric radiation exposure during the initial evaluation for blunt trauma.

BACKGROUND Increased utilization of computed tomography (CT) scans for evaluation of blunt trauma patients has resulted in increased doses of radiation to patients. Radiation dose is relatively amplified in children secondary to body size, and children are more susceptible to long-term carcinogenic effects of radiation. Our aim was to measure radiation dose received in pediatric blunt trauma patients during initial CT evaluation and to determine whether doses exceed doses historically correlated with an increased risk of thyroid cancer. METHODS A prospective cohort study of patients aged 0 years to 17 years was conducted over 6 months. Dosimeters were placed on the neck, chest, and groin before CT scanning to measure surface radiation. Patient measurements and scanning parameters were collected prospectively along with diagnostic findings on CT imaging. Cumulative effective whole body dose and organ doses were calculated. RESULTS The mean number of scans per patient was 3.1 ± 1.3. Mean whole body effective dose was 17.43 mSv. Mean organ doses were thyroid 32.18 mGy, breast 10.89 mGy, and gonads 13.15 mGy. Patients with selective CT scanning defined as ≤2 scans had a statistically significant decrease in radiation dose compared with patients with >2 scans. CONCLUSIONS Thyroid doses in 71% of study patients fell within the dose range historically correlated with an increased risk of thyroid cancer and whole body effective doses fell within the range of historical doses correlated with an increased risk of all solid cancers and leukemia. Selective scanning of body areas as compared with whole body scanning results in a statistically significant decrease in all doses.

Magnetic resonance imaging pelvimetry and the prediction of labor dystocia.

OBJECTIVE: To study whether magnetic resonance imaging (MRI) pelvimetry has the ability to identify those women who require cesarean delivery for labor dystocia. METHODS: From July 2003 to April 2004, nulliparous women scheduled for a labor induction for prolonged pregnancy (42 weeks) were asked to participate in a pelvimetry study. Those who consented underwent fast-acquisition MRI that included two 90-second acquisitions to evaluate fetal biometry and volumetry and maternal pelvimetry, including novel measurements of pelvic bony and soft tissue volumes as determined by MRI. Information about each patient’s pregnancy, labor course, and neonatal outcome was prospectively collected. Pelvimetry results for those women undergoing operative delivery for labor dystocia were compared with those who did not. Single fetal and maternal pelvic measurements, as well as ratios of both, were analyzed. In addition, previously described radiographic pelvimetry techniques and formulas to predict dystocia were used. RESULTS: One hundred one women underwent MRI, and 22 of these underwent cesarean delivery for dystocia. No single fetal measurement was statistically associated with dystocia. Several maternal pelvic measures, fetal-to-maternal ratios, and previously reported pelvimetric techniques were significantly associated with dystocia. The ratio of magnetic resonance (MR) fetal head volume to pelvic soft tissue volume had statistical significance (P = .04). Receiver operator characteristic curves were developed for the different measurements, ratios, and formulas studied to assess whether any of the techniques could accurately predict labor dystocia requiring operative delivery. The area under the curve values ranged from 0.6 to 0.8, with the ratio of MR head volume to pelvic soft tissue being 0.7. These values suggest that MRI can identify those women at greatest risk for dystocia, but it cannot with accuracy predict which ones will require a cesarean. CONCLUSION: We found significant associations with MRI pelvimetry and labor dystocia, but MRI was not a significant improvement over previously described pelvimetric techniques. LEVEL OF EVIDENCE: II-3

Estimation of Vessel Flow and Diameter during Cerebral Vasospasm Using Transcranial Doppler Indices

OBJECTIVE An important limitation of transcranial Doppler (TCD) ultrasonography is its inability to directly measure blood flow or vessel diameter. To extend the ability of TCD ultrasonography, indices were derived from an intensity-weighted mean of the entire Doppler spectrum. The objective of this article is to test the behavior of these indices under conditions of diameter constancy (hyper- and hypoventilation) and when vessel diameter decreases (vasospasm). METHODS A flow index (FI) was calculated by averaging several heartbeats of spectral data and calculating the first spectral moment. An area index (AI) was defined as the FI divided by the mean velocity, motivated by the knowledge that vessel flow is the product of vessel diameter and mean velocity. To test the FI and the AI under conditions of diameter constancy, middle cerebral artery Doppler signals were obtained from 20 patients during conditions of hypercarbia, hypocarbia, and normocarbia. To test the ability of these indices to evaluate a decrease in vessel diameter, signals from 41 sites on 23 arteries were obtained from patients who underwent both TCD and angiographic studies on two separate occasions after the occurrence of subarachnoid hemorrhage. The changes in the AI were compared with the arterial diameters measured from angiograms. RESULTS The FI was proportional to the mean velocity in the cohort of healthy patients (r=0.97). The AI changed by less than 3% in the same cohort. The AI predicted the direction of the diameter change in all vessels showing angiographic changes in area. Changes in the AI and the measured angiographic changes in cross-sectional areas were correlated (overall, r=0.90; with two outlines removed, r=0.86). CONCLUSION This variant of the intensity-weighted mean predicts changes in vessel cross-sectional area under conditions of changes in CO2 and cerebral vasospasm. This preliminary study suggests that careful use of this tool may provide accurate evaluation of cerebral blood flow through the large vessels and quantitative changes in diameter, which occur frequently after subarachnoid hemorrhage.

Oscillations in cerebral blood flow detected with a transcranial Doppler index.

Although transcranial Doppler ultrasound (TCD) has been used to detect oscillations in CBF, interpretation is severely limited, since only blood velocity and not flow is measured. Oscillations in vessel diameter could, therefore, mask or alter the detection of those in flow by TCD velocities. In this report, the authors use a TCD-derived index of flow to detect and quantify oscillations of CBF in humans at rest. A flow index (FI) was calculated from TCD spectra by averaging the intensity weighted mean in a beat-by-beat manner over 10 seconds. Both FI and TCD velocity were measured in 16 studies of eight normal subjects at rest every 10 seconds for 20 minutes. End tidal CO2 and blood pressure were obtained simultaneously in six of these studies. The TCD probe position was meticulously held constant. An index of vessel area was calculated by dividing FI by velocity. Spectral estimations were obtained using the Welch method. Spectral peaks were defined as peaks greater than 2 dB above background. The frequencies and magnitudes of spectral peaks of FI, velocity, blood pressure, and CO2 were compared with t tests. The Kolmogorov-Smirnov test was used to further confirm that the data were not white noise. In most cases, three spectral peaks (a, b, c) could be identified, corresponding to periods of 208 ± 93, 59 ± 31, and 28 ± 4 (SD) seconds for FI, and 196 ± 83, 57 ± 20, and 28 ± 6, (SD) seconds for velocity. The magnitudes of the spectral peaks for FI were significantly greater (P < 0.02) than those for velocity. These magnitudes corresponded to variations of at least 15.6%, 9.8%, and 6.8% for FI, and 4.8%, 4.2%, and 2.8% for velocity. The frequencies of the spectral peaks of CO2 were similar to those of FI with periods of 213 ± 100, 60 ± 46, and 28 ± 3.6 (SD) seconds. However, the CO2 spectral peak magnitudes were small, with an estimated maximal effect on CBF of (±) 2.5 ± 0.98, 1.5 ± 0.54, and 1.1 ± 0.31 (SD) percent. The frequencies of the blood pressure spectral peaks also were similar, with periods of 173 ± 81, 44 ± 8, and 26 ± 2.5 (SD) seconds. Their magnitudes were small, corresponding to variations in blood pressure of (±) 2.1 ± 0.55, 0.97 ± 0.25, and 0.72 ± 0.19 (SD) percent. Furthermore, coherence analysis showed no correlation between CO2 and FI, and only weak correlations at isolated frequencies between CO2 and velocity, blood pressure and velocity, or blood pressure and FI. The Kolmogorov-Smirnov test distinguished our data from white noise in most cases. Oscillations in vessel flow occur with significant magnitude at three distinct frequencies in normal subjects at rest and can be detected with a TCD-derived index. The presence of oscillations in blood velocity at similar frequencies but at lower magnitudes suggests that the vessel diameters oscillate in synchrony with flow. Observed variations in CO2 and blood pressure do not explain the flow oscillations. Ordinary TCD velocities severely underestimate these oscillations and so are not appropriate when small changes in flow are to be measured.

Evaluation of cerebral arterial flow with transcranial Doppler ultrasound: theoretical development and phantom studies.

Blood flow information available from transcranial Doppler ultrasound is usually derived from velocity alone because no knowledge of vessel caliber is available. In cases such as vasospasm, where vessel size changes, the inference of flow from velocity becomes questionable. A computational technique was used to calculate a flow index and 2 vessel area indices based on the first and zero moments of the Doppler power spectrum. These indices were tested in a steady and pulsatile flow phantom using 6 different diameter elastic tubes. Changes in the flow index showed good agreement with changes in timed volume flow for different flow rates. The vessel caliber indices correctly predicted changes in area when different diameter tubes were examined. These indices may prove useful in clinical settings where the constancy of flow or vessel diameter between studies are in question.

Radiation dose management: Part 1, minimizing radiation dose in CT-guided procedures

OBJECTIVE The purpose of this article is to discuss radiation dose during CT-guided interventions and to explain how radiologists can modify technical factors to minimize radiation doses. Scanner-displayed indexes of radiation exposure that are available during the procedure will be defined to increase awareness about CT radiation dose reduction during interventional procedures. CONCLUSION CT-guided fluoroscopic procedures are safe and effective methods of directed intervention; however, the increasing use of medical radiation is an important consideration. The appropriate use of imaging with an acceptable risk must be considered in every case. During CT-guided interventions, scanner parameters that can be used as a guide for effective dose management, including the CT dose index and dose-length product, are readily displayed. These parameters can be adjusted by modifying the longitudinal scan length, number of scans, and tube current-exposure time product (milliampere × second [mAs]). A team approach to radiation dose reduction will work the best.

MR volume of the fetal cerebellum in relation to growth.

To quantify fetal cerebellar growth by measuring cerebellar volumes of normal fetuses throughout gestation with MRI.

Comparison of fetal biometric values with sonographic and 3D reconstruction MRI in term gestations.

OBJECTIVE We sought to compare the fetal biometric values head and abdominal circumferences, biparietal and occipital-frontal diameters, and left and right ventricular atrial diameters obtained with contemporaneous sonography and 3D MRI reconstructions in term pregnancies. SUBJECTS AND METHODS A total of 107 nulliparous women evaluated as having uncomplicated pregnancies and scheduled for induction at 42 completed weeks gave their informed consent and underwent MRI and sonography within 3 hours of each other. Two single-shot fast spin-echo MRI sequences were performed with 7- and 4-mm slice thicknesses and no gap. A single observer performed MRI postprocessing to obtain biometric values. A single sonographer using a 3- to 5-MHz curvilinear transducer performed transabdominal sonography. Concordance correlation and Bland-Altman analysis of differences were performed. RESULTS Concordance correlation was poor for both right (0.024) and left (0.005) ventricular atrial diameters. There were moderate concordance correlations for head (0.56) and abdominal (0.53) circumferences and biparietal diameter (0.61). Occipital-frontal diameter had fair correlation (0.27). CONCLUSION Comparison between contemporaneous sonographic and 3D reconstructed MR images at late gestational ages shows acceptable correlation between the two techniques for head circumference, abdominal circumference, and biparietal diameter.