Christopher T. Whitlow

Arterial spin-labeled MR perfusion imaging: clinical applications.

Arterial spin labeling (ASL) imaging soon will be available as a routine clinical perfusion imaging sequence for a significant number of MR imaging scanners. The ASL perfusion technique offers information similar to that provided by conventional dynamic susceptibility sequences, but it does not require the use of an intravenous contrast agent, and the data can be quantified. The appearance of pathology is affected significantly by the ASL techniques used. Familiarity with the available sequence parameter options and the common appearances of pathology facilitates perfusion interpretation.

Abnormal white matter integrity related to head impact exposure in a season of high school varsity football.

The aim of this study was to determine whether the cumulative effects of head impacts from a season of high school football produce magnetic resonance imaging (MRI) measureable changes in the brain in the absence of clinically diagnosed concussion. Players from a local high school football team were instrumented with the Head Impact Telemetry System (HITS™) during all practices and games. All players received pre- and postseason MRI, including diffusion tensor imaging (DTI). Immediate Post-Concussion Assessment and Cognitive Testing (ImPACT) was also conducted. Total impacts and risk-weighted cumulative exposure (RWE), including linear (RWELinear), rotational (RWERotational), and combined components (RWECP), were computed from the sensor data. Fractional, linear, planar, and spherical anisotropies (FA, CL, CP, and CS, respectively), as well as mean diffusivity (MD), were used to determine total number of abnormal white matter voxels defined as 2 standard deviations above or below the group mean. Delta (post-preseason) ImPACT scores for each individual were computed and compared to the DTI measures using Spearmans rank correlation coefficient. None of the players analyzed experienced clinical concussion (N=24). Regression analysis revealed a statistically significant linear relationship between RWECP and FA. Secondary analyses demonstrated additional statistically significant linear associations between RWE (RWECP and RWELinear) and all DTI measures. There was also a strong correlation between DTI measures and change in Verbal Memory subscore of the ImPACT. We demonstrate that a single season of football can produce brain MRI changes in the absence of clinical concussion. Similar brain MRI changes have been previously associated with mild traumatic brain injury.

Imaging and Treatment of Sacral Insufficiency Fractures

SUMMARY: SIFs are a common, though often unsuspected, cause of low back pain in the elderly. Although numerous radiographic modalities can be used to diagnose SIFs, bone scintigraphy and MR imaging are the most sensitive. Conservative management involves various combinations of bed rest, rehabilitation, and analgesics. More recently, sacroplasty has emerged as an alternative therapy for the treatment of SIFs, with prospective studies and case reports suggesting that it is a safe and effective therapy. This article reviews the imaging appearance of SIFs and discusses treatment options with a focus on sacroplasty.

Effect of Resting-State Functional MR Imaging Duration on Stability of Graph Theory Metrics of Brain Network Connectivity

PURPOSE To investigate the effect of resting-state (RS) functional magnetic resonance (MR) imaging blood oxygen level-dependent (BOLD) signal acquisition duration on stability of computed graph theory metrics of brain network connectivity. MATERIALS AND METHODS An institutional ethics committee approved this study, and informed consent was obtained. BOLD signal (7.5 minutes worth) was obtained from 30 subjects and truncated into 30-second time bins that ranged from 1.5 to 7.5 minutes. A binarized adjacency matrix for each subject and acquisition duration was generated at network costs between 0.1 and 0.5, where network cost is defined as the ratio of the number of edges (connections) in a network to the maximum possible number of edges. Measures of correlation coefficient stability associated with functional connectivity matrices (correlation coefficient standard deviation [SD] and correlation threshold) and associated graph theory metrics (small worldness, local efficiency, and global efficiency) were computed for each subject at each BOLD signal acquisition duration. Computations were implemented with a 15-node 30-core computer cluster to enable analysis of the approximately 2000 resulting brain networks. Analysis of variance and posthoc analyses were conducted to identify differences between time bins for each measure. RESULTS Small worldness, local efficiency, and global efficiency stabilized after 2 minutes of BOLD signal acquisition, whereas correlation coefficient data from functional connectivity matrices (correlation coefficient SD and cost-associated threshold) stabilized after 5 minutes of BOLD signal acquisition. CONCLUSION Graph theory metrics of brain network connectivity (small worldness, local efficiency, and global efficiency) may be accurately computed from as little as 1.5-2.0 minutes of RS functional MR imaging BOLD signal. As such, implementation of these methods in the context of time-constrained clinical imaging protocols may be feasible and cost-effective. SUPPLEMENTAL MATERIAL http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.11101708/-/DC1.

Hypercapnia-Induced Cerebral Hyperperfusion: An Underrecognized Clinical Entity

BACKGROUND AND PURPOSE: The incidence of cerebral hyperperfusion and hypoperfusion, respectively, resulting from hypercapnia and hypocapnia in hospitalized patients is unknown but is likely underrecognized by radiologists and clinicians without routine performance of quantitative perfusion imaging. Our purpose was to report the clinical and perfusion imaging findings in a series of patients confirmed to have hypercapnic cerebral hyperperfusion and hypocapnic hypoperfusion. MATERIALS AND METHODS: Conventional cerebral MR imaging examination was supplemented with arterial spin-labeled (ASL) MR perfusion imaging in 45 patients during a 16-month period at a single institution. Patients presented with an indication of altered mental status, metastasis, or suspected stroke. Images were reviewed and correlated with arterial blood gas (ABG) analysis and clinical history. RESULTS: Patients ranged in age from 1.5 to 85 years. No significant acute findings were identified on conventional MR imaging. Patients with hypercapnia showed global hyperperfusion on ASL cerebral blood flow (CBF) maps, respiratory acidosis on ABG, and diffuse air-space abnormalities on same-day chest radiographs. Regression analysis revealed a significant positive linear relationship between cerebral perfusion and the partial pressure of carbon dioxide (pCO2; β, 4.02; t, 11.03; P < .0005), such that rates of cerebral perfusion changed by 4.0 mL/100 g/min for each 1-mm Hg change in pCO2. CONCLUSIONS: With the inception of ASL as a routine perfusion imaging technique, hypercapnic-associated cerebral hyperperfusion will be recognized more frequently and may provide an alternative cause of unexplained neuropsychiatric symptoms in hospitalized patients. In a similar fashion, hypocapnia may account for a subset of patients with normal MR imaging examinations with poor ASL perfusion signal.

Effects of the self-administration of ethanol and ethanol/sucrose on rates of local cerebral glucose utilization in rats

In a previous study, the voluntary ingestion of ethanol by rats was found to be associated with a discrete pattern of changes in functional activity that included the nucleus accumbens, medial prefrontal cortex, basolateral and central nuclei of the amygdala, as well as the ventral midbrain. Rats in this study, however, consumed a combination of ethanol in a sucrose vehicle. The purpose of the present experiment was to characterize the role of sucrose in determining the effects of orally self-administered ethanol using the quantitative autoradiographic 2-[14C]deoxyglucose (2DG) method for measurement of rates of local cerebral glucose utilization. A modified sucrose-substitution procedure was employed to train three groups of Wistar rats to self-administer either water, 10% ethanol (10E), or a 10% ethanol/2% sucrose solution (10E/2S) in daily sessions. An additional group of rats was trained using a modified acclimation procedure (home cage) in order to determine if any exposure to sucrose would alter rates of glucose utilization. Once stable rates of consumption were established, the 2DG method was applied immediately following completion of the final test session. Rats received a dose of ethanol equivalent to 0.5 g kg-1 on the day of the procedure or a comparable volume of water. Rates of energy metabolism were significantly increased in all three groups of rats that consumed ethanol (10E/2S, 10E, and home cage), as compared to rates in rats that consumed water. The areas of significant change included the rostral pole and posterior shell of the nucleus accumbens, medial prefrontal cortex, the basolateral and central nuclei of the amygdala, the ventral tegmental area, and the substantia nigra pars compacta. Thus, the pattern of changes in functional brain activity that accompanies voluntary ingestion of ethanol is independent of the vehicle in which the ethanol is presented or the procedures used to initiate consumption. Furthermore, these data demonstrate that it is the simultaneous activation of an interrelated network of limbic brain regions that serves as the substrate of the effects of ethanol self-administration.

High dimensional classification of structural MRI Alzheimer's disease data based on large scale regularization.

In this work we use a large scale regularization approach based on penalized logistic regression to automatically classify structural MRI images (sMRI) according to cognitive status. Its performance is illustrated using sMRI data from the Alzheimer Disease Neuroimaging Initiative (ADNI) clinical database. We downloaded sMRI data from 98 subjects (49 cognitive normal and 49 patients) matched by age and sex from the ADNI website. Images were segmented and normalized using SPM8 and ANTS software packages. Classification was performed using GLMNET library implementation of penalized logistic regression based on coordinate-wise descent optimization techniques. To avoid optimistic estimates classification accuracy, sensitivity, and specificity were determined based on a combination of three-way split of the data with nested 10-fold cross-validations. One of the main features of this approach is that classification is performed based on large scale regularization. The methodology presented here was highly accurate, sensitive, and specific when automatically classifying sMRI images of cognitive normal subjects and Alzheimer disease (AD) patients. Higher levels of accuracy, sensitivity, and specificity were achieved for gray matter (GM) volume maps (85.7, 82.9, and 90%, respectively) compared to white matter volume maps (81.1, 80.6, and 82.5%, respectively). We found that GM and white matter tissues carry useful information for discriminating patients from cognitive normal subjects using sMRI brain data. Although we have demonstrated the efficacy of this voxel-wise classification method in discriminating cognitive normal subjects from AD patients, in principle it could be applied to any clinical population.

Functional consequences of the repeated administration of Δ9-tetrahydrocannabinol in the rat

The repeated administration of Delta(9)-tetrahydrocannabinol (THC) results in tolerance to many of its behavioral and physiological effects. It also produces changes in the functionality of cannabinoid receptors. What is not completely understood is how these cellular events translate into the behavioral and physiological changes that are associated with repeated cannabinoid agonist treatment. The purpose of these studies was to determine the development of changes in the patterns of functional activity, as measured by the 2-[14C]deoxyglucose method (2DG), associated with repeated THC exposure. Male Sprague-Dawley rats (n=4-5) were administered THC (vehicle or 10 mg/kg, intraperitoneally), daily for 7 or 21 days. Fifteen minutes following the final THC treatment the 2DG procedure was initiated. In separate sets of rats similarly treated with THC, locomotor activity and core body temperature were measured at corresponding time points in order to establish the behavioral profile of repeated THC administration. The acute administration of THC following 7 or 21 days of drug exposure resulted in a significant attenuation of changes in rates of glucose utilization throughout the majority of brain regions analyzed when compared to the large global decreases observed following a single administration of THC. After 7 and 21 days of treatment, cerebral metabolic rates were no longer different from vehicle-treated controls in most cortical, thalamic and basal ganglia regions. This attenuation closely paralleled the development of tolerance to the effects of THC on locomotor activity and core body temperature. However, glucose utilization remained altered in the nucleus accumbens, mediodorsal thalamus, basolateral amygdala, portions of the hippocampus and median raphe. These data suggest that the development of tolerance to the cerebral metabolic effects of THC is regionally specific and temporally distinct. The persistence of effects in limbic areas as well as portions of the hippocampal complex, however, suggests that processes such as stress, reward, and aspects of memory mediated by these brain regions may continue to be affected by THC even after prolonged THC exposure.

Sacroplasty versus Vertebroplasty: Comparable Clinical Outcomes for the Treatment of Fracture-Related Pain

BACKGROUND AND PURPOSE: Little is known about the long-term clinical outcomes of sacroplasty, a relatively new minimally invasive percutaneous procedure for the treatment of sacral insufficiency fractures. The first purpose of the present study, therefore, was to investigate the effects of sacroplasty on pain, mobility, and activities of daily living (ADLs). A second purpose was to compare clinical outcomes of sacroplasty with those of vertebroplasty, a similar but more established procedure. MATERIALS AND METHODS: A retrospective case series of 12 patients who had a sacroplasty and a control group of 21 patients who had undergone a vertebroplasty was conducted. A 12-item questionnaire and subsequent telephone interview requested each patient to rate the intensity of pain, as well as the ability to ambulate and perform ADLs, before sacroplasty or vertebroplasty, and at the time of the interview. RESULTS: There was a statistically significant decrease in overall self-reported pain, as well as an increase in self-reported ability to ambulate and perform ADLs after sacroplasty or vertebroplasty. These improvements were equivalent, regardless of which procedure the patient received. CONCLUSION: The present study suggests that the treatment of sacral insufficiency fractures with sacroplasty produces relatively long-lasting improvements in pain, mobility, and the ability to perform ADLs. These data also suggest that the clinical outcomes of sacroplasty are comparable with those of vertebroplasty, an accepted and more routinely performed procedure.

Imaging Evidence and Recommendations for Traumatic Brain Injury: Advanced Neuro- and Neurovascular Imaging Techniques

Beyond the initial noncontrast CT, patients with brain trauma may be subjected to a variety of imaging studies. Here, the working group from the ACR Head Injury Institute discusses the use of these advanced imaging methods. SUMMARY: Neuroimaging plays a critical role in the evaluation of patients with traumatic brain injury, with NCCT as the first-line of imaging for patients with traumatic brain injury and MR imaging being recommended in specific settings. Advanced neuroimaging techniques, including MR imaging DTI, blood oxygen level–dependent fMRI, MR spectroscopy, perfusion imaging, PET/SPECT, and magnetoencephalography, are of particular interest in identifying further injury in patients with traumatic brain injury when conventional NCCT and MR imaging findings are normal, as well as for prognostication in patients with persistent symptoms. These advanced neuroimaging techniques are currently under investigation in an attempt to optimize them and substantiate their clinical relevance in individual patients. However, the data currently available confine their use to the research arena for group comparisons, and there remains insufficient evidence at the time of this writing to conclude that these advanced techniques can be used for routine clinical use at the individual patient level. TBI imaging is a rapidly evolving field, and a number of the recommendations presented will be updated in the future to reflect the advances in medical knowledge.