Current Medical Imaging - Volume 3, Issue 4, 2007

Functional imaging with various radioligands and single photon emission tomography (SPECT) or positron emission tomography (PET) has demonstrated many types of blood flow, glucose metabolic and neurochemical dysfunctions in a variety of neurological disorders. Functional neurotransmitter imaging is an evolving technique to detect neurotransmittersreleased during a task performance. Dr. Alan Fischman reports striatal and extrastriataldopamine neurotransmission during performance of a variety of cognitive and behavioral tasks. Dr. Biswas describes the role of SPECT and magnetic resonance imaging (MRI) for pre- and postoperative evaluation of childhood Moyamoya disease, which is characterized by chronic progressive stenosis leading to occulusion of carotid as well as anterior and middle carotid arteries. Imaging presynaptic dopaminergic markers provides key insights into the pathophysiology of Parkinson's disease (PD), which is characterized by bradykinesia, tremor, rigidity, and postural instability. Dr. Vijay Dhawan covers diagnostic and therapeutic applications of dopaminergic and metabolic imaging in PD and other movement disorders. Functional MRI has ushered in a new area in the imaging of cognitive brain activity and refines the management of patients with a variety of brain disorders while simultaneously revealing new insights into normal and abnormal cognitive function. Clinical applications have been on presurgical mapping of sensorimotor, language, and memory function as well as imaging of brain pathways mediating the emotions. Alzheimer's disease (AD) has been identified as a common form of dementia in the elderly, and its early, objective and quantitative indicators are important for clinical assessment and monitoring of therapeutic interventions. Dr. Frederik Giesel presents a recently developed post processing technique to segment and visulaize the ventricular system and measure ventricular volumes in patients with mild cognitive impairment and AD. Perfusion-weighted MRI is concerned with microscopic flow at the capillary level, and the contrast may be either endogenous or exogenous. Quantitative characterization of the full diffusion tensor is clinically avaliable, and diffusion anisotropy has been shown to vary widely within white matter. Diffusion tensor is a 3D data set in which each element inthe matrix has an associated magnitude and direction of diffusion. Dr. de Marco specifies the use of functional MRI data to explore putative networks of interconnected active areas and the various steps in the analysis of structural equation modeling (SEM) which uses theoretical and/or empirical hypotheses to estimate the effects (path coefficients) of an experimental task. Tracking gliomas dynamics on MRI has become important for therapeutic management. Dr. Hugues Duffau provides an extensive review of existing algorithms for the three computational tasks (image segmentation and registration as well as in silico growth modeling) involved in patient-specific tumor modeling. Interventional and surgical procedures in the abdomen or pelvis can result in urinary injury. Hemodynamically stable patients with microscopic hematuria are treated conservatively and probably do not need additional imaging. Multidetector CT (MDCT) is the method of choice for evaluating trauma patients with macroscopic hematuria and plays an important role in selecting treatment for the indivisual patient. A suspected vascular injury requires evaluation by CT angiography. Suspicion of injury to the renal collecting system or ureters needs delayed imaging during excretory phase. Dr. Maja Hrabak makes a pictorial review of iatrogenic urinary trauma diagnosed fast and accurately by MDCT cystography, urography and angiograpgy. Ultrasound contrast agents in conjunction with contrast specific imaging techniques are increasingly accepted in clinical use. Dr. Christian Gorg reports the use of sulfur hexafluoride based microbubble contrast medium (Sonovue) with contrastspecific continuous mode software (Acuson) for the diagnosis of various splenic pathology.

Functional neurotransmitter imaging (fNTI) is an evolving technique that uses molecular imaging to detect neurotransmitters released during a task performance. This technique provides a tool to study neurochemistry of human cognition and involves dynamic measurement of the concentration of a specific radioligand during the task performance. Since ligands are competitively displaced by endogenously released neurotransmitters, a reduction in ligand concentration during task performance indicates task-induced release of endogenous neurotransmitter. Most of the fNTI experiments have used a specific dopamine receptor ligand 11C-raclopride, which is suitable only for detection of dopamine released in the striatum. Ligands such as 18F-fallypride and 11C-FLB456 are potential candidates for detection of extrastriatal dopamine release. Using this technique, we have studied striatal and extrastriatal dopamine neurotransmission during performance of a variety of cognitive and behavioral tasks. These tasks include, motor planning, conscious and nonconscious motor memory, cured-recall, response inhibition and emotional memory. Since, fNTI is an emerging technique, it has so far been used to study only dopaminergic neurotransmission. Its utility in the study of human brain and cognition depends critically on the development of appropriate ligands for other neurotransmitters.

Moyamoya disease is a vascular disease of unknown aetiology characterized by chronic progressive stenosis leading to occlusion of the supraclinoid internal carotid arteries and the proximal anterior and middle cerebral arteries along with abundant collateral vessel formation. Clinically the disease manifests with features of cerebral ischaemia including recurrent TIA's, headache, seizures or motor deficits. Characteristic angiographic features on MR angiography and conventional angiography confirm diagnosis. However, as the presence of complete arterial occlusion on angiography does not reliably predict haemodynamic impairment, single photon emission computed tomography (SPECT) is indicated for quantitative assessment of regional cerebral blood flow. SPECT is thus employed to detect regional perfusion instability prior to treatment and to determine the extent of improvement of functional perfusion after treatment. Affected patients with recurrent or progressive cerebral ischemic episodes and haemodynamic deficits SPECT findings require surgical management aimed at improving blood supply to the hypoperfused ischaemic cortical regions. The most commonly suggested revascularization procedure for children is encephaloduroarteriosynangiosis (EDAS). We describe an illustrative case report of 7-year-old boy who presented with sudden-onset of left sided hemiparesis. Findings on CT, MRI and SPECT were consistent with a diagnosis of moyamoya disease with acute cerebral infarction. The boy underwent encephaloduroarteriosynangiosis twice with good outcome. Motor power in his left extremities improved from grade 1 to 3 without cognitive deficit. Postoperative MRI confirmed vascular patency while SPECT showed satisfactory cerebral perfusion consistent with his clinical outcome. We thus conclude that MRI and SPECT are invaluable tools in pre and postoperative evaluation of patients with moyamoya disease.

PET imaging first played an important role in the diagnosis of Parkinson's disease (PD) approximately 20 years ago when studies using the newly developed radiotracer, [18F]fluorodopa, demonstrated a clear dopamine loss in the basal ganglia. Other radiotracers were then developed to image presynaptic dopamine transporters, vesicular monoamine transporters and postsynaptic D2 receptor sites. These studies enhanced our understanding of the way in which the dopaminergic system is altered in PD. Shortly after [18F]fluorodeoxyglucose was used to quantify the expression of metabolic brain patterns in PD patients by comparing them with similar studies conducted in healthy volunteers. This dual approach of studying both dopamine and metabolism in the brain has now been applied successfully to diagnose and differentiate typical and atypical parkinsonian syndromes. These imaging biomarkers have since been applied to assess the effects of dopaminergic therapy and surgical techniques like pallidotomy, subthalamic stimulation, embryonic cell implantation, intraputaminal nerve growth factor infusion and viral vector gene therapy.

Objectives: Clear, objective, quantitative and early indicators of Alzheimer disease (AD) are important for clinical assessment and monitoring of therapeutic interventions. In this article, we present a recently developed post processing technique to segment and visualize the ventricular system and measure ventricular volumes in patients with mild cognitive impairment (MCI) and AD. We applied this method to quantify temporal horn volumes (THV) and the temporal horn index (THI, ratio of temporal horn volume to lateral ventricular volume) and compared the results with both a direct measurement of the hippocampal formation, and neuropsychological test performance. The aim of this article is to present the two most common methods of direct and indirect measurement and their possible limitations in comparison to the neuropsychologic scoring. Methods and materials: All subjects (21 healthy controls, 21 patients with MCI and 10 patients with AD) underwent extensive neuropsychological testing and were scanned using a 1.5 T MRI (Magnetom Vision, Siemens, Germany). A direct measurement of the hippocampal formation was produced via high-resolution T1-weighted volume imaging, while indirect temporal horn volume (THV) was calculated using a watershed algorithm-based software package (MeVis, Germany). Results: In all subjects, a successful direct and indirect quantification of the hippocampus was performed or the THV and THI were calculated. For both the manual and the semi-automated approach, a significant volume difference was found between healthy volunteers and AD patients (p<0.001). Group analysis also showed a significant difference between the THV as well as THI of AD patients compared to MCI subjects and controls (p<0.005). There was a significant negative correlation between the neuropsychological performance and both THV and THI (p<0.01) as well as a significant correlation of direct and indirect measurement (p<0.001). Conclusion: The fast and rapid development of post processing imaging techniques now allow an easy and objective method of performing hippocampal volumetry. These recently developed post processing techniques presented accurate results which are comparable to the conventional direct approach, while offering a faster and more automated technique of assessing THV and THI that could be used as an indicator of AD in a clinical context and may be helpful in studying therapeutic intervention.

Functional neuroimaging first allowed researchers to describe the functional segregation of regionally activated areas during a variety of experimental tasks. More recently, functional integration studies have described how these functionally specialized areas (i.e. areas whose activity is temporally modified) interact within a highly distributed neural network. When applied to the field of functional magnetic resonance imaging (fMRI), structural equation modeling (SEM) uses theoretical and/or empirical hypotheses to estimate the effects (path coefficients) of an experimental task within a putative network. Structural equation modeling represents a linear technique for multivariate analysis of fMRI data and has been developed to simultaneously examine ratios of multiple causality in an experimental design; the method attempts to explain a covariance structure within an anatomical (constrained) model. This method, when combined with the concept of effective connectivity, can provide information on the strength and direction of the functional interactions which take place between identified nodes of a putative network. After having provided a brief reminder of the principle of the blood oxygen level-dependent (BOLD) contrast effect, the physiological bases of brain activity and the concepts of functional integration and effective connectivity, we specify the various steps in the SEM analysis and the use of fMRI data to explore putative networks of interconnected active areas.

Tracking gliomas dynamics on MRI has became more and more important for therapeutic management. Powerful computational tools have been recently developed in this context enabling in silico growth on a virtual brain that can be matched with real 3D segmented evolution through registration between atlases and patient brain MRI data. In this paper, we provide an extensive review of existing algorithms for the three computational tasks involved in patient-specific tumor modeling: image segmentation, image registration, and in silico growth modelling (with special emphasis on the proliferation-diffusion model). Accuracy and limits of the reviewed algorithms are systematically discussed. Finally applications of these methods for both clinical practice and fundamental research are also discussed.

Abdomino-pelvic interventional and surgical procedures can result in iatrogenic urinary tract injury. Radiological diagnosis can be difficult to establish because findings are caused by iatrogenic trauma, and by underlying disease and therapeutical procedures. We performed multidetector computed tomography (MDCT) in patients with suspected urinary tract trauma with scanning protocol selected according to the suspected type of injury: non-enhanced scanning for detection of fluid collections, MDCT angiography for renal parenchymal and vascular changes, MDCT urography for pelvicalyceal and ureteric injuries, and MDCT cystography for bladder and urethral lesions. The injuries were found after urologic, general surgical and gynaecological/obstetric procedures. Renal parenchymal injuries were caused by blunt (extracorporeal shock-wave lithotripsy) or penetrating trauma (renal biopsy), with formation of subcapsular, perinephric and/or paranephric haematomas. Renal vascular pedicle changes after kidney transplantation were precisely defined using MDCT angiography. MDCT urography depicted leakage of contrast material from the pelvicalyceal system after nephron-sparing surgery, from the ureter after kidney transplantation, and from bladder tear after caesarean section, while urethral injury after bladder catheterization was diagnosed using MDCT cystography. MDCT angiography and/or MDCT urography present methods for evaluation of iatrogenic urinary tract trauma because they enable fast and accurate diagnosis and planning of surgical and interventional procedures.

Objective: Ultrasound contrast agents in conjunction with contrast specific imaging techniques, are increasingly accepted in clinical use for diagnostic imaging in several organs. Contrast enhanced sonography (CES) of second generation contrast media have shown a spleen-specific uptake of the microbubble contrast agent. The aim of this review is to illustrate indications for the use of CES in patients with suspected (peri-)splenic pathology. Methods: This pictorial review based on the experience of transcutaneous CES in 180 consecutive adult patients with (peri-)splenic pathology diagnosed by B-mode sonography at an internal medicine center. CES studies were performed with a contrast-devoted unit (Acuson, Sequoia, Siemens medical solution) that had contrast-specific, continuous-mode software. A low mechanical index was used. A sulfur hexafluoride-based microbubble contrast medium (Sonovue®, Bracco SpA, Milan, Italy) was injected. Results: On our experience there are six clinical conditions which indicates the use of CES for diagnosis of (peri-)splenic pathology: 1. the perisplenic tumor, 2. the small sized spleen, 3. the inhomogenous spleen of unknown cause, 4. the incidentally found hypoechoic splenic tumor, and 5. pain in the left upper quadrant, and 6. patients with blunt abdominal trauma. CES is of value 1. to diagnose or exclude accessory spleen, 2. to diagnose functional asplenia/hyposplenia, 3. to diagnose focal lesions in an inhomogenous spleen, 4. to diagnose high vascular splenic hemangioma, 5. to diagnose or exclude splenic infarction and splenic abscess, and 6. to diagnose splenic laceration. Conclusion: CES is of diagnostic value in several clinical circumstances to diagnose accessory spleen, functional asplenia, small sized splenic involvement, high vascular splenic hemangioma, and vascular splenic pathology like splenic infarction, splenic abscess, and splenic laceration.

The Figure No. 2 was mistakenly inverted in the article entitled “TMS&fMRI - A New Neuroimaging Combinational Tool to Study Brain Function” published in Current Medical Imaging Reviews 2007; 3(2): 109-115.