SUMMARY: Conebeam x-ray CT (CBCT) is a developing imaging technique designed to provide relatively low-dose high-spatial-resolution visualization of high-contrast structures in the head and neck and other anatomic areas. This first installment in a 2-part review will address the physical principles underlying CBCT imaging as it is used in dedicated head and neck scanners. Concepts related to CBCT acquisition geometry, flat panel detection, and image quality will be explored in detail. Particular emphasis will be placed on technical limitations to low-contrast detectability and radiation dose. Proposed methods of x-ray scatter reduction will also be discussed.C onebeam x-ray CT (CBCT) is a relatively recent installment in the growing inventory of clinical CT technologies. Although the first prototype clinical CBCT scanner was adapted for angiographic applications in 1982, the emergence of commercial CBCT scanners was delayed for more than a decade. 1 The arrival of marketable scanners in the last 10 years has been, in part, facilitated by parallel advancements in flat panel detector (FPD) technology, improved computing power, and the relatively low power requirements of the x-ray tubes used in CBCT. These advancements have allowed CBCT scanners to be sufficiently inexpensive and compact for operation in office-based head and neck as well as dental imaging applications. These systems are distinguished by a conical x-ray beam geometry and the use of 3D reconstruction algorithms; most recent models are also fit with FPDs. As they are employed for specific imaging tasks in restricted anatomic regions such as the head and neck, preliminary research suggests that they can produce images with high isotropic spatial resolution while delivering a relatively low patient dose. This first part in a series of 2 articles will review the physical principles underlying CBCT as it is employed in head and neck diagnostic imaging. C-arm CBCT systems used in the interventional suite and CBCT systems used in radiation therapy have been the subject of other reviews.2-4 Although there are numerous differences between CBCT and conventional fan-beam CT techniques, many of the fundamental physical concepts are the same. Fundamental Principles of CTThe original clinical CT scanner was introduced by Sir Godfrey N. Hounsfield in 1967. Data acquisition was based on a translaterotate parallel-beam geometry wherein pencil beams of x-rays were directed at a detector opposite the source and the transmitted intensity of photons incident on the detector was measured. The gantry would then both translate and rotate to capture x-ray attenuation data systematically from multiple points and angles.5 Although x-ray sources, acquisition geometries, and detectors have rapidly evolved since Hounsfield's original scanner, the theory behind CT has not changed.The attenuation of a monochromatic x-ray beam through a homogeneous object is described by the Lambert-Beer law:where I is the transmitted photon intensity, I o is the original intensity, x is the lengt...

SUMMARY: Conebeam x-ray CT (CBCT) is being increasingly used for point-of-service head and neck and dentomaxillofacial imaging. This technique provides relatively high isotropic spatial resolution of osseous structures with a reduced radiation dose compared with conventional CT scans. In this second installment in a 2-part review, the clinical applications in the dentomaxillofacial and head and neck regions will be explored, with particular emphasis on diagnostic imaging of the sinuses, temporal bone, and craniofacial structures. Several controversies surrounding the emergence of CBCT technology will also be addressed. C onebeam CT (CBCT) is an advancement in CT imagingthat has begun to emerge as a potentially low-dose crosssectional technique for visualizing bony structures in the head and neck. The physical principles, image quality parameters, and technical limitations relevant to CBCT imaging were discussed in Part 1 of this 2-part series. The second part presented here will highlight the evidence related to CBCT applications in head and neck as well as dentomaxillofacial imaging. Controversial aspects of this technology will also be addressed, including limitations in image quality and its often officebased operational model.CBCT was first adapted for potential clinical use in 1982 at the Mayo Clinic Biodynamics Research Laboratory. 1 Initial interest focused primarily on applications in angiography in which soft-tissue resolution could be sacrificed in favor of high temporal and spatial-resolving capabilities. Since that time, several CBCT systems have been developed for use both in the interventional suite and for general applications in CT angiography. 2,3 Exploration of CBCT technologies for use in radiation therapy guidance began in 1992, 4,5 followed by integration of the first CBCT imaging system into the gantry of a linear accelerator in 1999. 6 The first CBCT system became commercially available for dentomaxillofacial imaging in 2001 (NewTom QR DVT 9000; Quantitative Radiology, Verona, Italy). Comparatively low dosing requirements and a relatively compact design have also led to intense interest in surgical planning and intraoperative CBCT applications, particularly in the head and neck but also in spinal, thoracic, abdominal, and orthopedic procedures. [7][8][9][10][11] Diagnostic applications in CT mammography and head and neck imaging are also under evaluation. 12-14 The technical and clinical considerations pertaining to CBCT imaging in many of these applications have been the subjects of several recent reviews. [15][16][17][18][19] The recent review by Dörfler et al 16 of the neurointerventional applications of CBCT is of particular interest to the field of neuroradiology.The discussion below will focus on the diagnostic and treatment-planning applications of CBCT in dentomaxillofacial and head and neck imaging. Commercially available CBCT systems for dentomaxillofacial imaging include the CB MercuRay and CB Throne (Hitachi Medical, Kashiwi-shi, Chiba-ken, Japan), 3D Accuitomo products (J. Mor...

Intestinal ischemia, which refers to insufficient blood flow to the bowel, is a potentially catastrophic entity that may require emergent intervention or surgery in the acute setting. Although the clinical signs and symptoms of intestinal ischemia are nonspecific, CT findings can be highly suggestive in the correct clinical setting. In this chapter we review the CT diagnosis of arterial, venous, and non-occlusive intestinal ischemia. We discuss the vascular anatomy, pathophysiology of intestinal ischemia, CT techniques for optimal imaging, key and ancillary radiological findings, and differential diagnosis. In the setting of an acute abdomen, rapid evaluation is necessary to identify intraabdominal processes that require emergent surgical intervention (1). While a wide-range of intraabdominal diseases may be present from trauma to inflammation, one of the most feared disorders is mesenteric ischemia, also known as intestinal ischemia, which refers to insufficient blood flow to the bowel (2). Initial imaging evaluation for intestinal ischemia is typically obtained with CT. Close attention to technique and search for key radiologic features with relation to the CT technique is required. Accurate diagnosis depends on understanding the vascular anatomy, epidemiology, and pathophysiology of various forms of mesenteric ischemia and their corresponding radiological findings on MDCT. At imaging, not only is inspection of the bowel itself important, but evaluation of the mesenteric fat, vasculature, and surrounding peritoneal cavity also helps improves accuracy in the diagnosis of bowel ischemia.

SUMMARY: ITB pumps are widely used in the treatment of intractable spasticity for many clinical indications, including cerebral palsy and spinal cord injury. High-dose intrathecal administration places the patient at significant risk for withdrawal in the event of device malfunction, necessitating rapid and complete evaluation of the pump-catheter system. This article reviews the approach to imaging evaluation of ITB pump-catheter systems, with specific emphasis on radiography, fluoroscopy, CT, and nuclear scintigraphy.ABBREVIATIONS: AP ϭ anteroposterior; DTPA ϭ diethylene-triamine pentaacetic acid; GABA ϭ gamma-aminobutyric acid;111 In ϭ Indium-111; IT ϭ intrathecal; ITB ϭ intrathecal baclofen; Tc99m ϭ technetium-99m

Background and Purpose-Lesion volume measured on MRI has been used as an objective surrogate marker for outcome in clinical trials. However, lesion volumes vary over time because of edema and tissue loss. This study aims to determine if lesion volumes measured at 30 and 90 days after ictus significantly differ. Methods-We performed a retrospective study of 18 patients who had acute (Ͻ24 hours) DWI and follow-up fluid-attenuated inversion recovery imaging at 5, 30, and 90 days. Two expert readers segmented lesions and the mean volumes of both reads were used in all statistical analyses. Results-Patient age was 65.8 (SD, 13.7) years and median NIHSS at baseline was 11.5. Inter-rater variability for lesion volume measurements was 3. [2][3][4][5] DWI is used to detect ischemia during the acute period; 6 T 2 -weighted fluid-attenuated inversion recovery (FLAIR) imaging can likewise be used to visualize vasogenic edema and infarction in the subacute and chronic stages. 7 Standards of lesion measurement have been produced, 8 and acute lesion evolution in various settings has been investigated extensively. 9 -14 Less extensive, however, is the investigation of lesion volume during the chronic stage despite the use of final infarct volume as an outcome measure. There is no consensus of when final occurs, although 30 days 2,3 and 90 days 4,5 have been used as imaging end points in clinical trials. Earlier outcome times minimize both loss to follow-up and the occurrence of confounding adverse events unrelated to the acute intervention. The purpose of this study is to determine if lesion volume measured at 90 days could be approximated at 5 or 30 days, thereby reducing time to imaging outcome while remaining rigorous in a definition of final infarct volume. Patients and Methods PatientsThis is a retrospective analysis of patients who consented to a natural history protocol between June 2000 and January 2006. Inclusion criteria required an imaging-confirmed diagnosis of ischemic stroke that affected the anterior circulation, a baseline lesion volume Ͼ2 mL on DWI obtained within 24 hours of time last known well, and successful follow-up FLAIR imaging at Ϸ5, 30, and 90 days. Patients scanned at all time points were more likely to have received thrombolytic therapy. Patients with evidence of acute hemorrhage were excluded. Image AnalysisImages were blinded to patient identifiers and time point. Lesions were traced according to the segmentation method described elsewhere 8 by 2 expert readers (M.R.G. and M.L.) using MIPAV (Medical Image Processing, Analysis, and Visualization, BIRSS; NIH, Bethesda, Md). Acute lesions were identified from traceweighted, diffusion-weighted images. Lesions on follow-up were identified from FLAIR images. Typical imaging parameters were as follows: DWI: bϭ0, 1000 sec/mm 2 , TR/TE Ϸ6000/72 ms; FLAIR: TR/TE Ϸ9000/140 ms; TI Ϸ2200 ms; FOVϭ22 cm; matrixϭ256ϫ128ϫ40; NEXϭ1; and resolutionϭ0.85ϫ1. Statistical AnalysisValues are reported as mean (SD [range]) unless otherwise noted. Normality was tested us...

Mesenteric inflammatory veno-occlusive disease (MIVOD) is a rare cause of inflammatory enterocolitis whose clinical and imaging presentation can be confused with mesenteric venous thrombosis and inflammatory bowel disease. We report two cases of histologically proven MIVOD in patients presenting with abdominal pain and describe potentially useful distinguishing features at contrast-enhanced CT, including prominent small pericolonic arteries and veins but a diminutive or absent inferior mesenteric vein. Alerting referring clinicians to the possibility of this diagnosis may help avoid unnecessary anticoagulation and reduce diagnostic delay. Treatment of MIVOD is surgical resection, which is typically curative.

Background Differentiating esthesioneuroblastoma (ENB) from other sinonasal tumors is difficult by MRI. We tested whether diffusion weighted imaging (DWI) could distinguish ENB from other sinonasal tumors. Methods Hundred forty‐six patients underwent sinonasal MRI, 75 with technically successful DWI. Pathology: 18 ENB (24%), 34 (45%) other malignant tumors, and 23 (31%) benign lesions. Apparent diffusion coefficients (ADCs) were calculated. Results Average ADC and normalized ADC of ENB (1.22 × 10−3 ± 0.28 mm2/s and 1.55 ± 0.36, respectively) were higher than other malignancies (0.98 × 10−3 ± 0.18 mm2/s and 1.31 ± 0.29, P = .002 and P = .034) and lower than benign disease (1.92 × 10−3 ± 0.33 mm2/s and 2.44 ± 0.50, P < .0001). ADC differentiated ENB from benign disease with 91% sensitivity and 83% specificity. An ADC cutoff of 1.1 × 10−3 mm2/s differentiated other malignancies from ENB with 72% sensitivity and 85% specificity. Conclusions DWI is useful in distinguishing ENB from other sinonasal disease.

SUMMARY:Arterial selection for reference time-enhancement curve generation in deconvolutionbased perfusion CT (PCT) studies of the head and neck is underevaluated. This study of 11 patients with confirmed head and neck squamous cell carcinoma demonstrates significant correlation (range, r ϭ 0.85-0.95) between perfusion parameter values derived with internal carotid artery (ICA) as compared to an external carotid artery reference, supporting the use of the ICA as arterial reference in PCT studies of the neck. P erfusion CT (PCT) is a rapid noninvasive imaging technique conceived originally to assess qualitatively and quantitatively regional cerebral blood flow (rCBF), cerebral blood volume (CBV), mean transit time (MTT), and later capillary permeability surface-area product (PS) within regions of interest (ROIs) in the brain.