Joseph J. Chen

CT Angiography of the Cardiac Valves: Normal, Diseased, and Postoperative Appearances

Although echocardiography remains the principal imaging technique for assessment of the cardiac valves, contrast material-enhanced electrocardiographically gated computed tomographic (CT) angiography is proving to be an increasingly valuable complementary modality in this setting. CT angiography allows excellent visualization of the morphologic features and function of the normal valves, as well as of a wide range of valve diseases, including congenital and acquired diseases, infectious endocarditis, and complications of valve replacement. The number, thickness, and opening and closing of the valve leaflets, as well as the presence of valve calcification, can be directly observed. CT angiography also permits simultaneous assessment of the valves and coronary arteries, which may prove valuable in presurgical planning. Unlike echocardiography and magnetic resonance imaging, however, CT angiography requires ionizing radiation and does not provide a direct measure of the valvular pressure gradient. Nevertheless, with further development of related imaging techniques, CT angiography can be expected to play an increasingly important role in the evaluation of the cardiac valves. Supplemental material available at http://radiographics.rsna.org/cgi/content/full/29/5/1393/DC1.

Use of a computer-aided detection system to detect missed lung cancer at chest radiography.

PURPOSE To study the ability of a computer-aided detection (CAD) system to detect lung cancer overlooked at initial interpretation by the radiologist. MATERIALS AND METHODS Institutional review board approval was given for this study. Patient consent was not required; a HIPAA waiver was granted because of the retrospective nature of the data collection. In patients with lung cancer diagnosed from 1995 to 2006 at two institutions, each chest radiograph obtained prior to tumor discovery was evaluated by two radiologists for an overlooked lesion. The size and location of the nodules were documented and graded for subtlety (grades 1-4, 1 = very subtle). Each radiograph with a missed lesion was analyzed by a commercial CAD system, as was the follow-up image at diagnosis. An age- and sex-matched control group was used to assess CAD false-positive rates. RESULTS Missed lung cancer was found in 89 patients (age range, 51-86 years; mean age, 65 years; 80 men, nine women) on 114 radiographs. Lesion size ranged from 0.4 to 5.5 cm (mean, 1.8 cm). Lesions were most commonly peripheral (n = 63, 71%) and in upper lobes (n = 67, 75%). Lesion subtlety score was 1, 2, 3, or 4 on 43, 49, 17, and five radiographs, respectively. CAD identified 53 (47%) and 46 (52%) undetected lesions on a per-image and per-patient basis, respectively. The average size of lesions detected with CAD was 1.73 cm compared with 1.85 cm for lesions that were undetected (P = .47). A significant difference (P = .017) was found in the average subtlety score between detected lesions (score, 2.06) and undetected lesions (score, 1.68). An average of 3.9 false-positive results occurred per radiograph; an average of 2.4 false-positive results occurred per radiograph for the control group. CONCLUSION CAD has the potential to detect approximately half of the lesions overlooked by human readers at chest radiography.

MR imaging of the brain in fat embolism syndrome

Fat embolism syndrome (FES) is an uncommon but serious complication of traumatic injury and is frequently diagnostically challenging. In this paper, the authors present four patients who sustained lower extremity long bone injury and who had a normal Glasgow Coma Scale before orthopedic surgical intervention. However, postoperatively, significant neurological deterioration developed in these patients. While cranial computed tomography (CT) obtained immediately after surgery for acutely altered mental status was negative in two of the four patients, brain magnetic resonance imaging (MRI) demonstrated white and gray matter abnormalities accounting for the impaired neurological status in all cases. MRI findings in conjunction with clinical presentation established the diagnosis in all patients. MRI is indicated in any patient with orthopedic injuries who manifests an unexplained acute alteration in mental status, despite a normal head CT.

RECIST versus volume measurement in medical CT using ellipsoids of known size.

Two hundred eighty three uniaxial ellipsoids with sizes from 4 mm to 11 mm were measured with a coordinate measuring matching (CMM) and also scanned using a medical computed tomography (CT) machine. Their volumes were determined by counting voxels over a threshold, as well as using equivalent volumes from the length given by the RECIST 1.1 criterion (Response Evaluation Criteria in Solid Tumors). The volumetric measurements yield an order of magnitude reduction in residuals compared to the CMM measurements than the residuals of the RECIST measurements also compared to the CMM measurements.

Continuing challenges in defining image quality

To achieve significant dose reduction without compromising diagnostic efficacy, it is important to understand the effects of exposure reduction on image quality, a concept that is often mentioned but not well defined in the imaging literature. Studies to assess subjective image quality for digital radiography (DR) demonstrate wide variability among radiologists and technologists, resulting in substantial variability in the determination of acceptable image quality and optimal radiation exposure required to obtain a high-quality radiograph. In addition to improving detector technology and image processing techniques and tailoring exposure to the exam type and patient body habitus, it is possible to take advantage of informatics-based and psychoperceptual approaches. These can be used to establish the relative trade-offs among patient exposure, perceived image quality, and diagnostic efficacy. Innovations such as automated quality assessment of digital radiographs, use of a mathematical model of the human visual system to predict the perceived impact of lower radiation exposure, the creation of a quality-assessment database of images, and better definition and training of radiologists in the determination of image quality can help to reduce variability in assessment and facilitate reductions in dose while minimizing negative effects on image quality.

Facial Recognition Software Success Rates for the Identification of 3D Surface Reconstructed Facial Images: Implications for Patient Privacy and Security

Image de-identification has focused on the removal of textual protected health information (PHI). Surface reconstructions of the face have the potential to reveal a subject’s identity even when textual PHI is absent. This study assessed the ability of a computer application to match research subjects’ 3D facial reconstructions with conventional photographs of their face. In a prospective study, 29 subjects underwent CT scans of the head and had frontal digital photographs of their face taken. Facial reconstructions of each CT dataset were generated on a 3D workstation. In phase 1, photographs of the 29 subjects undergoing CT scans were added to a digital directory and tested for recognition using facial recognition software. In phases 2–4, additional photographs were added in groups of 50 to increase the pool of possible matches and the test for recognition was repeated. As an internal control, photographs of all subjects were tested for recognition against an identical photograph. Of 3D reconstructions, 27.5% were matched correctly to corresponding photographs (95% upper CL, 40.1%). All study subject photographs were matched correctly to identical photographs (95% lower CL, 88.6%). Of 3D reconstructions, 96.6% were recognized simply as a face by the software (95% lower CL, 83.5%). Facial recognition software has the potential to recognize features on 3D CT surface reconstructions and match these with photographs, with implications for PHI.

A low-cost density reference phantom for computed tomography.

The authors characterized a commercially available foam composed of polyurethane and polyisocyanurate which is marketed for modeling parts in the aircraft, automotive, and related industries. The authors found that the foam may be suitable for use as a density reference standard in the range below -400 Hounsfield units. This range is coincident with the density of lung tissue. The foam may be helpful in making the diagnosis of lung disease more systematic.

Computed tomography assessment of valvular morphology, function, and disease.

Recent advancement in computed tomography angiography (CTA) has enabled the noninvasive delineation of cardiac valves using this method. Although echocardiography is the current standard, CTA is a valuable complementary imaging method to evaluate valvular morphology and function. In addition, CTA may contribute to the assessment of both congenital and acquired valvular heart disease, infectious endocarditis, and postsurgical complications of valve replacement.

MDCT diagnosis and endovascular management of bullet embolization to the heart

Multidetector computed tomography is a useful imaging modality in diagnosing the path of a bullet and evaluating the extent of injury the bullet has caused in the torso. We present a 21-year-old patient who sustained a single gunshot wound to the right flank without any exit wound. Bullet fragments were embolized to the heart and left pulmonary artery via inferior vena cava. Minimally invasive interventional management was performed successfully to retrieve the intracardiac bullet fragments to prevent further complications.

Evaluation of Low-Contrast Detectability of Iterative Reconstruction across Multiple Institutions, CT Scanner Manufacturers, and Radiation Exposure Levels.

PURPOSE To compare image resolution from iterative reconstruction with resolution from filtered back projection for low-contrast objects on phantom computed tomographic (CT) images across vendors and exposure levels. MATERIALS AND METHODS Randomized repeat scans of an American College of Radiology CT accreditation phantom (module 2, low contrast) were performed for multiple radiation exposures, vendors, and vendor iterative reconstruction algorithms. Eleven volunteers were presented with 900 images by using a custom-designed graphical user interface to perform a task created specifically for this reader study. Results were analyzed by using statistical graphics and analysis of variance. RESULTS Across three vendors (blinded as A, B, and C) and across three exposure levels, the mean correct classification rate was higher for iterative reconstruction than filtered back projection (P < .01): 87.4% iterative reconstruction and 81.3% filtered back projection at 20 mGy, 70.3% iterative reconstruction and 63.9% filtered back projection at 12 mGy, and 61.0% iterative reconstruction and 56.4% filtered back projection at 7.2 mGy. There was a significant difference in mean correct classification rate between vendor B and the other two vendors. Across all exposure levels, images obtained by using vendor Bs scanner outperformed the other vendors, with a mean correct classification rate of 74.4%, while the mean correct classification rate for vendors A and C was 68.1% and 68.3%, respectively. Across all readers, the mean correct classification rate for iterative reconstruction (73.0%) was higher compared with the mean correct classification rate for filtered back projection (67.0%). CONCLUSION The potential exists to reduce radiation dose without compromising low-contrast detectability by using iterative reconstruction instead of filtered back projection. There is substantial variability across vendor reconstruction algorithms.