David L. Clark

Limits of 8-Tesla magnetic resonance imaging spatial resolution of the deoxygenated cerebral microvasculature.

To quantify the minimum magnetic resonance imaging (MRI) spatial resolution of the visible deoxygenated microscopic vessels of the human brain at 8 T.

Comparison of local sine wave modeling with harmonic phase analysis for the assessment of myocardial strain.

To compare local sine‐wave modeling (SinMod) with harmonic phase analysis (HARP), for assessment of left ventricular (LV) circumferential strain (εcc) from tagged cardiovascular magnetic resonance images.

Quantification of left ventricular indices from SSFP cine imaging: Impact of real-world variability in analysis methodology and utility of geometric modeling

To assess the impact of “real‐world” practice variation in the process of quantifying left ventricular (LV) mass, volume indices, and ejection fraction (EF) from steady‐state free precession cardiovascular magnetic resonance (CMR) images. The utility of LV geometric modeling techniques was also assessed.

Vestibular Stimulation for ADHD: Randomized Controlled Trial of Comprehensive Motion Apparatus

Objective: This research evaluates effects of vestibular stimulation by Comprehensive Motion Apparatus (CMA) in ADHD. Method: Children ages 6 to 12 (48 boys, 5 girls) with ADHD were randomized to thrice-weekly 30-min treatments for 12 weeks with CMA, stimulating otoliths and semicircular canals, or a single-blind control of equal duration and intensity, each treatment followed by a 20-min typing tutorial. Results: In intent-to-treat analysis (n = 50), primary outcome improved significantly in both groups (p = .0001, d = 1.09 to 1.30), but treatment difference not significant (p = .7). Control children regressed by follow-up (difference p = .034, d = 0.65), but overall difference was not significant (p = .13, d = .47). No measure showed significant treatment differences at treatment end, but one did at follow-up. Children with IQ-achievement discrepancy ≥ 1 SD showed significantly more CMA advantage on three measures. Conclusion: This study illustrates the importance of a credible control condition of equal duration and intensity in trials of novel treatments. CMA treatment cannot be recommended for combined-type ADHD without learning disorder. (J. of Att. Dis. 2008; 11(5) 599-611)

Effects of Rocking on Neuromuscular Development in the Premature

It has been postulated that motion stimulation accelerates postnatal development. To test this hypothesis, 26 premature infants participated in a randomized controlled study of the effects of rocking on body weight gain and measures of neuromuscular development. Treatment infants were exposed to 15-min sessions of sinusoidal oscillation about the longitudinal axis, three times a day for 2 weeks. Infants were evaluated at the beginning and end of the 2-week treatment period and 2 weeks later. Neuromuscular development at these three times was measured with the comprehensive Dubowitz examination. Following treatment, large as compared with small premature infants showed a marked, but not statistically significant increase in weight gain. Duration of treatment appears to be a critical factor in influencing weight gain. All infants exposed to motion stimulation showed significant gains over controls in overall neuromuscular development. Passive muscle tone (posture, arm recoil and popliteal angle) and active motility (arm traction, head lag and ventral suspension) showed significant improvement in the treatment group at posttest. Similar results were recorded with auditory and visual orientation, alertness and defensive reaction. These specific areas of behavior have been recognized to be delayed in premature infants not exposed to a program of sensory stimulation.

Postrotatory nystagmus in the full-term and premature infant

Postrotatory nystagmus (PR-N) is an easily elicited reflex reported to be abnormal in developmentally delayed children. PR-N has been recorded in newborns, but methodological difficulties have compromised its full understanding. Eight healthy adults were compared with 15 full-term and 12 premature infants, all neurologically normal, who were tested serially during the first year of life. All subjects were positioned in a rotational chair, spun for 1 min at a constant angular velocity (150 degrees/s) and then abruptly stopped. Primary and secondary PR-N was electronically recorded. Results for full-terms and prematures were similar in all variables, but the number and frequency of beats in both primary and secondary PR-N were significantly greater in adults. Angular displacement and velocity of each beat was significantly higher in infants of all ages. All components of PR-N, whether primary or secondary, can be identified in infants under 1 year of age and are clearly different from those observed in adults. These differences may reflect anatomical and neurophysiological immaturity of eye movement control in the infant.

Effects of chronic 2g centrifugation on equilibrium behavior in the rat

Mature rats were exposed to chronic centrifugation at 2 g for 60 days. A rail test was utilized to quantitatively evaluate equilibrium behavior in a static and dynamic situation after return to the earth standard 1g environment. Exposure to chronic centrifugation was shown to significantly alter equilibrium behavior. The 2 g animals showed greater disequilibrium than 1 g control animals under both static and dynamic situations. The differences between the two groups increased under more dynamic test conditions. A mechanism is suggested to account for these differences.

Histological validation of dynamic-equilibrium cardiovascular magnetic resonance for the measurement of myocardial extracellular volume

Background Extracellular matrix expansion is fundamental to left ventricular (LV) remodeling, and is a therapeutic target. CMR techniques are increasingly used to evaluate myocardial extracellular volume (ECV), however the most widely applied methods are without histological validation. The aim of this study was to provide whole-heart, histological validation of; 1. Dynamic-equilibrium CMR (DynEq-CMR), where ECV is quantified using hematocrit-adjusted myocardial and blood T1 values measured before and after gadolinium bolus; and 2. Isolated measurement of myocardial T1 at a fixed time-point following gadolinium bolus, used as an ECV surrogate.

Response to letter regarding article, "Comprehensive validation of cardiovascular magnetic resonance techniques for the assessment of myocardial extracellular volume".

We acknowledge that with 6 subjects, the power of our study to assess the significance of between-subject correlation is limited and cannot rule out an underlying significant relationship.1 However, the small observed value of correlation (−0.21), outwith its significance, certainly provides no evidence of a meaningful relationship between postcontrast myocardial T1 and histological collagen volume fraction. Requiring a large number of patients for a correlation to become significant is not the hallmark of a good biomarker. Indeed, we are somewhat surprised by the line of argument taken by Iles and Taylor in their letter. There is great interest and impetus in this field and a major aim within the T1 mapping community is to develop a technology that may be able to help with not only …

Development of Postrotatory Nystagmus Time Constants

Models of the slow phase portion of postrotatory nystagmus in the adult include time constants which describe primary and secondary nystagmus. The cupular time constant (T1) is believed to reflect the activity of the cupula of the semicircular canal, while the adaptation time constant (Ta) defines the rate of change of the baseline firing rate. Values for T1 and Ta have been published for the adult. In this study 37 normal infants under one year of age and 12 children, 3 to 13 years of age were examined for postrotatory nystagmus, and values for the two time constants were determined. The cupular time constant does not change with age and is concluded to be at an adult level at birth. This is correlated with the relative maturity of ear morphology at birth. The adaptation time constant increases from 79.5 sec at one month of age to 260.7 sec at 12-13 years of age, implying that maturation of adaption is a relatively slow process.