Jeff L. Creasy

High-Resolution 7T MRI of the Human Hippocampus In Vivo

To describe an initial experience imaging the human hippocampus in vivo using a 7T magnetic resonance (MR) scanner and a protocol developed for very high field neuroimaging.

Evaluating Contrast-Enhancing Brain Lesions in Patients with AIDS by Using Positron Emission Tomography

As many as 80% of patients with the acquired immunodeficiency syndrome (AIDS) are reported at autopsy to have central nervous system involvement [1], and approximately 10% develop focal brain lesions [2]. Most of these lesions are due to toxoplasmosis or primary central nervous system lymphoma, and definitive diagnosis requires brain biopsy [3, 4]. The high incidence and treatability of toxoplasmosis has led to the current recommendation that brain biopsy be reserved for those patients in whom empiric therapy for toxoplasmosis has failed or who present with lesions atypical for toxoplasmosis [5-7]. Many biopsies done under these guidelines will show primary central nervous system lymphoma [8, 9]. An imaging method that reliably differentiates between toxoplasmosis and lymphoma would allow prompt treatment of lymphoma and obviate the need for brain biopsy. Positron emission tomography can measure regional metabolic activity within tissue with a sensitivity and specificity similar to that of radioimmunoassay when used with specific labeled substrates [10]. By measuring the accumulation of fluorodeoxyglucose F-18, it can distinguish malignant brain tumors from surrounding normal tissue [11]. Experience at our institution and elsewhere [12] indicates that positron emission tomography can accurately differentiate between lymphoma and nonmalignant causes of central nervous system lesions in patients with AIDS. We did a study to determine whether evaluating contrast-enhancing central nervous system lesions in patients with AIDS by using Toxoplasma serologic testing and positron emission tomography can accurately differentiate between lymphoma and nonlymphoma diagnoses. Methods Our prospective clinical study was approved by the Vanderbilt University Committee for the Protection of Human Subjects. All patients with AIDS at Vanderbilt University Medical Center who had contrast-enhancing central nervous system lesions shown by computed tomography or magnetic resonance imaging between May 1991 and March 1993 were eligible. Patients were excluded only for failure to give informed consent. Eligible patients received a history; a physical examination; a computed tomographic or magnetic resonance imaging scan, or both; a positron emission tomographic scan; a Toxoplasma serologic test; a cerebrospinal fluid examination (if clinically indicated); a serum cryptococcal antigen test; and a CD4+ T-cell count. Autopsy consent was obtained prospectively to enable us to confirm diagnoses that remained in question. Computed tomography was done on a Siemens Somatom Plus (Siemens Medical Systems, Iselin, New Jersey) using 10-mm thick transaxial slices before and after infusion of intravenous contrast material. Magnetic resonance imaging was done on a 1.5-Tesla Siemens Magnatom SP (Siemens Gammasonics, Hoffman Estates, Illinois) using standard T1-weighted, proton density, and T2-weighted sequences before contrast and T1-weighted images after infusion of gadolinium-diethylenetriamine pentaacetic acid. Positron emission tomographic scans were obtained using a Siemens emission computed axial tomograph 933-08-16 scanner (Siemens Gammasonics) with inplane resolution of 6.5 mm and axial resolution of 8 mm. This scanner provides 15 simultaneously acquired tomographic frames over a 12.8-cm view. Images were obtained 45 minutes after the administration of 10 mCi of 2-fluorodeoxyglucose F-18 using two bed positions, 30 scans each, 4 mm apart. All patients had transmission scans for a measured attenuation correction. Counts were normalized to a homogeneous mixture of brain tissue. Lesions were considered hypometabolic if their measured activity was roughly equal to or less than the activity of white matter. Hypermetabolic lesions had at least 1.5 times the activity of white matter. (Figures 1 and 2) show the magnetic resonance and positron emission tomographic images of two patients in our study. Figure 1 is taken from patient 4, who had toxoplasmosis; Figure 2 is taken from patient 12, who had lymphoma. The magnetic resonance imaging scans are nearly identical in appearance, but the positron emission tomographic scans show hypometabolic and hypermetabolic lesions, respectively. Figure 1. Central nervous system toxoplasmosis associated with the acquired immunodeficiency syndrome. Top. Bottom. Figure 2. Lymphoma associated with the acquired immunodeficiency syndrome. Top. Bottom. Toxoplasma (IgG) serologic testing was done by immunofluorescent assay, and results were considered positive if the titer was 1:4. Autopsies were done by one of us using standard human immunodeficiency virus (HIV) precautions. After 2 weeks fixation in 10% formalin, lesions were evaluated with hematoxylin-eosin, Giemsa, Gomori methenamine silver, periodic acid-Schiff, and methyl green-pyronine stains and appropriate immunohistochemistry. Treatment The therapeutic decisions for each patient were ultimately made by the attending physicians, but therapy was recommended by the protocol on the basis of the schema given in Table 1. Patients with positive Toxoplasma serologic test results and positron emission tomographic scans that showed hypometabolic lesions were assumed to have toxoplasmosis, and antitoxoplasmosis therapy was recommended. Negative serologic test results and a positron emission tomographic scan showing hypermetabolic lesions were considered indicative of lymphoma, and empiric cranial irradiation was recommended. Patients with positive serologic test results and positron emission tomographic scans that showed hypermetabolic lesions were considered to have lymphoma, and empiric cranial irradiation was recommended. Empiric antitoxoplasmosis therapy was allowed in this situation at the discretion of the attending physician. Patients with negative serologic test results and a positron emission tomographic scan showing hypometabolic lesions were considered to be candidates for brain biopsy if an alternative diagnosis was not established. Although this schema was developed to guide therapy, in some cases the actual treatment received was different from that recommended. For example, patient 9 (Table 2) had positive serologic test results and hypermetabolic lesions on a positron emission tomographic scan. The protocol would have allowed both antitoxoplasmosis therapy and radiation therapy. In fact, the patient received only radiation therapy. Similarly, patient 12 (Table 2) had hypermetabolic lesions on a positron emission tomographic scan and negative serologic test results. He received a brain biopsy even though this was not recommended by the protocol. The differences between the recommended treatment and the actual treatment received do not bias the results because confirmation of diagnoses was dependent on the actual treatment received. Table 1. Therapy Recommended for Patients with AIDS and Contrast-Enhancing Central Nervous System Mass Lesions on the Basis of Toxoplasma Serologic Testing and Positron Emission Tomographic Scanning Table 2. Major Diagnostic Findings and Diagnoses in Evaluable Patients with Contrast-Enhancing Central Nervous System Mass Lesions* Patients were followed longitudinally, and a repeated computed tomographic or magnetic resonance imaging scan, or both, was obtained after approximately 2 weeks and then at varying intervals, depending on clinical response. Clinical and radiologic findings were evaluated to determine response to therapy. Diagnoses were confirmed by clinical and radiologic improvement or resolution in response to a single type of therapy (such as antibiotics compared with radiation); by autopsy; or, in one case, by brain biopsy. Patients who had clinical and radiologic improvement in response to more than one type of therapy were only considered to have a confirmed diagnosis if it was confirmed by autopsy or brain biopsy. Results Twenty patients with focal, contrast-enhancing central nervous system lesions were enrolled in the study between May 1991 and June 1993. Two patients were not evaluable because their diagnoses could not be confirmed. Table 2 lists the confirmed diagnoses and major diagnostic findings in the 18 evaluable patients. Confirmation of Diagnoses Eight patients had toxoplasmosis; six of these diagnoses were confirmed by clinical and radiologic response to therapy and two were confirmed by autopsy. Six patients had lymphoma: One diagnosis was confirmed by clinical and radiologic response, one by stereotactic biopsy, and four by autopsy. Two patients with progressive multifocal leukoencephalopathy and one with a cerebral cryptococcoma had their diagnoses confirmed by autopsy. One patient had clinical and radiologic responses to therapy directed at both toxoplasmosis and tuberculosis; he remains alive at 9 months. Results of Serologic Testing and Positron Emission Tomographic Scanning Toxoplasma serologic testing was done in seven of the eight patients with toxoplasmosis, and all results were positive (range, 1:10 to 1:32 768). Three of the six patients with lymphoma also had positive serologic test results. Seven patients with toxoplasmosis each had a positron emission tomographic scan, and all scans showed hypometabolic lesions. In contrast, the six patients with lymphoma all had hypermetabolic lesions on positron emission tomographic scans. The difference between these two sets of results was highly significant (P < 0.001, Fisher exact test, two-tailed). Four patients had other diagnoses. Patient 17 had a cryptococcoma, negative Toxoplasma serologic test results, and hypometabolic lesions on a positron emission tomographic scan. Two patients had progressive multifocal leukoencephalopathy; the positron emission tomographic scans showed hypometabolic lesions in one and hypermetabolic lesions in the other. In patient 18, who had clinical and radiologic responses to therapy directed at both toxoplasmosis and tuberculosis, the positron emission tomographic scan showed hypometabolic lesions. Discussion Cerebral t

Gadolinium‐enhanced magnetic resonance imaging in bell's palsy

Inflammation of the facial nerve in Bells palsy can be demonstrated on gadolinium‐enhanced magnetic resonance imaging. We have studied a series of 17 Bells palsy patients with gadolinium‐enhanced magnetic resonance imaging, and the purpose of this paper is to report our findings and discuss their significance. Most acute Bells palsy cases demonstrate facial nerve enhancement, usually in the distal internal auditory canal and labyrinthine/geniculate segments. Other segments demonstrate enhancement less often. Gadolinium enhancement occurs regardless of the severity of the paralysis and can persist after clinical improvement of the paralysis. The findings of this study corroborate other evidence that the segments of the facial nerve most often involved in Bells palsy are the only segments that are most often enhanced with gadolinium‐enhanced magnetic resonance imaging. The role of gadolinium‐enhanced magnetic resonance imaging in the management of Bells palsy patients is discussed.

Magnetic resonance perfusion/diffusion imaging of the excised dog kidney

RATIONALE AND OBJECTIVES The authors developed a model of tissue capillary beds applicable to perfusion/diffusion imaging with magnetic resonance imaging (MRI). The model consists of a formalin-fixed excised dog kidney attached to a variable speed pump. With this system, it is possible to perfuse the kidney at selected rates. METHODS Using the intravoxel incoherent motion model (IVIM), the apparent diffusion coefficient (ADC), diffusion coefficient (D), and perfusion fraction (f) were computed for a region of interest (ROI) in the renal cortex and in the medulla of seven kidneys, one of which was injected with a vasodilator before fixation. ADC and D values were computed for both cortex and medulla. These values were normalized to zero flow and plotted against renal perfusion. The perfusion fraction f was expressed in percent and was not normalized to zero flow. RESULTS Normalized ADC and f were correlated with tissue perfusion rates using the Spearman rank-sum test (n = 18, rs greater than 0.5, P less than or equal to .02 for the standard preparation in both cortex and medulla), whereas normalized D (rs much less than 0.5) was uncorrelated for both preparations in cortex and medulla. CONCLUSIONS The isolated perfused dog kidney is a useful model of tissue capillary beds for perfusion imaging technique development. The perfusion/diffusion-related parameters ADC and f increase as flow increases in the tissues, whereas D does not.

Magnetic Resonance Angiography Techniques

&NA; Price RR, Creasy JL, Lorenz CH, Partain CL. Magnetic resonance angiography techniques. Invest Radiol 1992;27:S27‐S32. After a radio frequency pulse, the decay of the magnetic resonance (MR) signal is described by two relaxation processes, T1 and T2. T1 describes the rate at which the magnetization realigns itself along the external magnetic field direction (ML), and T2 describes the rate of decay of the magnetization component along the transverse axis (MT). Magnetic resonance angiography (MRA) sequences have been developed that encode flow as changes in the apparent T1 or T2 of the moving blood relative to stationary tissues. MRA sequences typically use either time‐of‐flight (TOF) techniques to encode T1 or phase‐contrast techniques to encode T2. TOF techniques encode flow as an apparent T1 shortening through the wash‐in of fully relaxed blood from outside the image volume. The shorter T1 produces an enhancement of vascular structures relative to stationary tissues. TOF methods may use either sequential two‐dimensional, three‐dimensional, or multi‐slab three‐dimensional imaging sequences to produce a three‐dimensional MRA data set. Phase‐contrast methods use additional magnetic field gradients to encode flow as shifts in the phase of MT. Both TOF and phase‐contrast methods use maximum intensity projection (MIP) images displayed in a cine format to aid in the visualization of three‐dimensional vascular structures.

Magnetic resonance imaging of neurocysticercosis.

Neurocysticercosis (NCC) is involvement of the central nervous system (CNS) by the porcine tapeworm. common in developing countries with poor sanitation. The disease has been noted increasingly in nonendemic areas because of travel and immigration from atlected regions. The magnetic resonance (MR) appearance can be characteristic. with single or multiple cysts and varying degrees of wall enhancement and surrounding edema, depending on the stage of the life cycle of the larva and its associated cyst.

ACR Appropriateness Criteria® on Cerebrovascular Disease

Stroke is the sudden onset of focal neurologic symptoms due to ischemia or hemorrhage in the brain. Current FDA-approved clinical treatment of acute ischemic stroke involves the use of the intravenous thrombolytic agent recombinant tissue plasminogen activator given <3 hours after symptom onset, following the exclusion of intracerebral hemorrhage by a noncontrast CT scan. Advanced MRI, CT, and other techniques may confirm the stroke diagnosis and subtype, demonstrate lesion location, identify vascular occlusion, and guide other management decisions but, within the first 3 hours after ictus, should not delay or be used to withhold recombinant tissue plasminogen activator therapy after the exclusion of acute hemorrhage on noncontrast CT scans. MR diffusion-weighted imaging is highly sensitive and specific for acute cerebral ischemia and, when combined with perfusion-weighted imaging, may be used to identify potentially salvageable ischemic tissue, especially in the period >3 hours after symptom onset. Advanced CT perfusion methods improve sensitivity to acute ischemia and are increasingly used with CT angiography to evaluate acute stroke as a supplement to noncontrast CT. The ACR Appropriateness Criteria(®) are evidence-based guidelines for specific clinical conditions that are reviewed every 2 years by a multidisciplinary expert panel. The guideline development and review include an extensive analysis of current medical literature from peer-reviewed journals and the application of a well-established consensus methodology (modified Delphi) to rate the appropriateness of imaging and treatment procedures by the panel. In those instances in which evidence is lacking or not definitive, expert opinion may be used to recommend imaging or treatment.

Ganglioglioma of the pineal gland: clinical and radiographic response to stereotactic radiosurgical ablation.

Case Report This 10-year-old, right-handed male third grader presented with a 3month history of behavioral changes followed by abulia, &dquo;dizziness,&dquo; ataxia, and urinary incontinence. His apathy and inactivity were initially attributed to a grief reaction after the death of a great-grandfather. However, a week before admission, his ataxia worsened, impairing safe ambulation. He had urinary incontinence for 1 to 2 days before admission. He did not complain of headache or double vision. His medical history was otherwise noncontributory. On examination, he was afebrile and normotensive. Abnormal findings were confined to the neurologic examination. He was inattentive, with flat affect and no spontaneous movements. Although disoriented to date and place, memory was intact. The cranial nerve examination revealed swollen optic discs. His color vision was significantly impaired bilaterally, and he had no stereopsis (by Titmus test). Confrontation fields showed a generalized constriction bilaterally, worse nasally. Regarding ocular motility, he was orthotropic but had impaired pursuit bilaterally. He had normal horizontal and vertical saccades, with no impairment of upgaze. Convergence was present but a little slow. His pupils reacted briskly to light. There was a limited upward gaze, and gaze evoked nystagmus in all directions. Cerebellar signs revealed severe axial ataxia with a positive Romberg sign. The sensory examination was indeterminate. There was no corticospinal tract deficit. Visual acuity, without correction, was 9/200 and 6/200, there was no improvement with pinhole, and his near vision was worse than J14 OU. Analysis of the cerebrospinal fluid revealed no cells or elevations in a-fetoprotein, #-human choriogonadotropin, chorioembryonic antigen, the lactate dehydrogenase 5 isoenzyme, or placental alkaline phosphatase. Neurodiagnostic imaging demonstrated a 2.7-cm mass in the

Design and evaluation of a flow phantom.

RATIONALE AND OBJECTIVES We constructed a near-anatomically correct large-vessel phantom to perform repeatable flow dynamics research examinations by angiography, magnetic resonance (MR) angiography, and computed tomography (CT) angiography. METHODS An internal carotid artery was constructed within a head phantom. The internal carotid artery branches into a middle and an anterior cerebral artery; the former trifurcates and ends in the superior sagittal sinus, and the latter ends in the inferior sagittal sinus. A transverse and sigmoid sinus drains the model. All four vessels connecting the arterial and venous vessels have variable flow-constricting ligatures placed around them. These ligatures are accessible on the skull surface. The skull cavity is filled with a silicone polymer that is isodense to brain on CT scans and isointense on most MR images. RESULTS The flow in the phantoms vessels may be varied in a repeatable manner. Multiple scan sequences may be performed without the image degradation caused by patient motion. The homogeneity of the filler polymer allows visualization of flow-related artifacts that may be hidden by complex human anatomy. CONCLUSION Preliminary images of each modality show promise for use of the phantom in imaging research on large-vessel flow dynamics.

Clinical Impact of Picture Archiving and Communication Systems: Evaluation of a Prototype System

Opinion surveys were gathered before and 6 months after installation of a prototype picture archiving and communication system (PACS) (PACS/1, Siemens Medical Systems, Iselin, NJ). Median turnaround times and the percent of delayed or missing reports were calculated for 1,026 baseline and 8,438 follow-up studies at 6 months. Neuroradiological (neuro) computed tomography (CT) used PACS, while neuro magnetic resonance (MR), body CT, and body MR served as controls. The opinion surveys showed improved service in all categories, including those not directly affected by PACS. PACS images favorably impressed 86% of respondents, but most considered the system too slow, unreliable, and the storage capacity too low. A majority of 81% recommended against purchase of PACS now. There was an overall increase in the median report turnaround time for both neuro CT and the controls. Neuro CT showed a 41% decrease in delayed or missing reports, but controls also showed similar decreases. The effects of this prototype PACS on turnaround time or on report delivery could not be distinguished from section-wide changes in CT and MR services. Future improvements in PACS should vigorously address increased speed, reliability, and storage capacity.