The effect of the antiscatter grid on full-field digital mammography phantom images.
Computer Analysis of Mammography Phantom Images (CAMPI) is a method for making quantitative measurements of image quality. This article reports on a recent application of this method to a prototype full-field digital mammography (FFDM) machine. Images of a modified ACR phantom were acquired on the General Electric Diagnostic Molybdenum Rhodium (GE-DMR) FFDM machine at a number of x-ray techniques, both with and without the scatter reduction grid. The techniques were chosen so that one had sets of grid and non-grid images with matched doses (200 mrads) and matched gray-scale values (1500). A third set was acquired at constant 26 kVp and varying mAs for both grid conditions. Analyses of the images yielded signal-to-noise-ratio (SNR), contrast and noise corresponding to each target object, and a non-uniformity measure. The results showed that under conditions of equal gray-scale value the grid images were markedly superior, albeit at higher doses than the non-grid images. Under constant dose conditions, the non-grid images were slightly superior in SNR (7%) but markedly less uniform (60%). Overall, the grid images had substantially greater contrast and superior image uniformity. These conclusions applied to the whole kVp range studied for the Mo-Mo target filter combination and 4 cm of breast equivalent material of average composition. These results suggest that use of the non-grid technique in digital mammography with the GE-DMR-FFDM unit, is presently not warranted. With improved uniformity correction procedure, this conclusion would change and one should be able to realize a 14% reduction in patient dose at the same SNR by using a non-grid technique. (+info)
A new filtering algorithm for medical magnetic resonance and computer tomography images.
Inner views of tubular structures based on computer tomography (CT) and magnetic resonance (MR) data sets may be created by virtual endoscopy. After a preliminary segmentation procedure for selecting the organ to be represented, the virtual endoscopy is a new postprocessing technique using surface or volume rendering of the data sets. In the case of surface rendering, the segmentation is based on a grey level thresholding technique. To avoid artifacts owing to the noise created in the imaging process, and to restore spurious resolution degradations, a robust Wiener filter was applied. This filter working in Fourier space approximates the noise spectrum by a simple function that is proportional to the square root of the signal amplitude. Thus, only points with tiny amplitudes consisting mostly of noise are suppressed. Further artifacts are avoided by the correct selection of the threshold range. Afterwards, the lumen and the inner walls of the tubular structures are well represented and allow one to distinguish between harmless fluctuations and medically significant structures. (+info)
Computerized analysis of abnormal asymmetry in digital chest radiographs: evaluation of potential utility.
The purpose of this study was to develop and test a computerized method for the fully automated analysis of abnormal asymmetry in digital posteroanterior (PA) chest radiographs. An automated lung segmentation method was used to identify the aerated lung regions in 600 chest radiographs. Minimal a priori lung morphology information was required for this gray-level thresholding-based segmentation. Consequently, segmentation was applicable to grossly abnormal cases. The relative areas of segmented right and left lung regions in each image were compared with the corresponding area distributions of normal images to determine the presence of abnormal asymmetry. Computerized diagnoses were compared with image ratings assigned by a radiologist. The ability of the automated method to distinguish normal from asymmetrically abnormal cases was evaluated by using receiver operating characteristic (ROC) analysis, which yielded an area under the ROC curve of 0.84. This automated method demonstrated promising performance in its ability to detect abnormal asymmetry in PA chest images. We believe this method could play a role in a picture archiving and communications (PACS) environment to immediately identify abnormal cases and to function as one component of a multifaceted computer-aided diagnostic scheme. (+info)
3D angiography. Clinical interest. First applications in interventional neuroradiology.
3D angiography is a true technical revolution that allows improvement in the quality and safety of diagnostic and endovascular treatment procedures. 3D angiography images are obtained by reconstruction of a rotational angiography acquisition done on a C-arm (GE Medical Systems) spinning at 40 degrees per second. The carotid or vertebral selective injection of a total of 15 ml of non-ionic contrast media at 3 ml/sec over 5 seconds allows the selection of the "arterial phase". Four hundred sixty 3D angiographic studies were performed from December 1996 to September 1998 on 260 patients and have been analyzed in MIP (Maximum Intensity Projection) and SSD (Shaded Surface Display) views. The exploration of intracranial aneurysms is simplified and only requires, for each vascular axis, a biplane PA and Lateral run followed by a single rotational angiography run. The 3D angiography image is available on the workstation's screen (Advantage Workstation 3.1, GE Medical Systems) in less than 10 minutes after the acquisition of the rotational run. It therefore allows one to analyze, during the intervention, the aneurysm's angioarchitecture, in particular the neck, and select the best therapeutic technique. When endovascular treatment is the best indication, 3D angiography allows one to define the optimal angle of view and accurately select the microcoils dimensions. 3D angiography replaces the multiple oblique views that used to be required to analyze the complex aneurysms and therefore allows a reduction of the total contrast medium quantity, the patient X-ray dose and the length of the intervention time which is a safety factor. Also, in particular for complex cases, it brings additional elements complementing the results of standard 2D DSA and rotational angiograms. In the cervical vascular pathology, 3D angiography allows for a better assessment of the stenosis level and of dissection lesions. Our current research activities focus on the matching without stereotactic frame between 3D X-ray angiography and volumetric MR acquisition, which should allow us to improve the treatment of intracerebral arterio-venous malformations (AVMs). (+info)
Radiolucent lines and component stability in knee arthroplasty. Standard versus fluoroscopically-assisted radiographs.
The radiolucent lines and the stability of the components of 66 knee arthroplasties were assessed by six orthopaedic surgeons on conventional anteroposterior and lateral radiographs and on fluoroscopic views which had been taken on the same day. The examiners were blinded as to the patients and clinical results. The interpretation of the radiographs was repeated after five months. On fluoroscopically-assisted radiographs four of the six examiners identified significantly more radiolucent lines for the femoral component (p < 0.05) and one significantly more for the tibial implant. Five examiners rated more femoral components as radiologically loose on fluoroscopically-assisted radiographs (p = 0.0008 to 0.0154), but none did so for the tibial components. The mean intra- and interobserver kappa values were higher for fluoroscopically-assisted radiographs for both components. We have shown that fluoroscopically-assisted radiographs allow more reproducible, and therefore reliable, detection of radiolucent lines in total knee arthroplasty. Assessment of the stability of the components is significantly influenced by the radiological technique used. Conventional radiographs are not adequate for evaluation of the stability of total knee arthroplasty and should be replaced by fluoroscopically-assisted films. (+info)
Ectopic eruption of the maxillary canine quantified in three dimensions on cephalometric radiographs between the ages of 5 and 15 years.
The eruption paths of 20 ectopic maxillary canine teeth (10 right, 10 left) were measured in three dimensions on annual lateral and depressed postero-anterior cephalometric radiographs of 15 patients between the ages of 5 and 15 years and compared with the eruption of normal canines. It was found that between the ages of 8 and 12 years ectopic canines on the left side moved more anteriorly than the normally erupting canines and the same was true of the right canines between the ages of 7 and 12 years. While the ectopic canines moved occlusally, their vertical movement was less than normal which accounts for the clinical finding that canines are impacted in the palate at a high level. The average palatally ectopic canine always moves palatally, and never shares in the buccal movement shown by normally erupting canines between the ages of 10 and 12 years. It was interesting to find that the differences between growth of normal and ectopic canines in the lateral plane of space are present as early as 5-6 years. (+info)
Angiographic correlation of CT calcification in the carotid siphon.
BACKGROUND AND PURPOSE: Calcification in the coronary arteries has been correlated with significant vessel stenosis. The predictive value of calcification within the carotid siphon has not been characterized; however, stenosis in the carotid siphon is potentially important in determining management of patients with ipsilateral carotid bifurcation stenosis. The purpose of this study was to determine optimal parameters for assessing carotid siphon calcification on head CT scans and to compare the CT findings with angiographic results. METHODS: We performed a retrospective review of patients referred for diagnostic carotid arteriography. Those patients who also had undergone a head CT study at our institution were selected. The CT scans and angiograms of 64 patients (128 vessels) were reviewed. Carotid siphon calcification on CT scans was characterized on brain and bone windows as mild, moderate, or severe. Comparison was then made with angiographic findings. RESULTS: The sensitivity and specificity of CT for depicting greater than 50% angiographic stenosis in the carotid siphon were 86% and 98%, respectively, for bone windows and 100% and 0%, respectively, for brain windows. The positive predictive value (PPV) for a stenosis of greater than 50% as evidenced by severe calcification was 86% on bone windows and 11% on brain windows. The PPV for mild and moderate calcification on bone windows was 2.5% and 0%, respectively. CONCLUSION: Severe CT calcification in the carotid siphon as characterized on bone windows correlates with a carotid siphon stenosis of greater than 50% as determined angiographically. Therefore, the identification of severe calcification offers a potential noninvasive method for identifying stenosis of the carotid siphon. This information may be essential in determining management and prognosis for patients with carotid bifurcation stenosis. (+info)
Calcification in chronic maxillary sinusitis: comparison of CT findings with histopathologic results.
BACKGROUND AND PURPOSE: It is important to differentiate fungal from nonfungal sinusitis in order to determine the optimal treatment for chronic sinusitis. The purpose of this study was to describe the CT findings of calcifications in chronic fungal and nonfungal maxillary sinusitis. METHODS: Five hundred ten patients with pathologically proved chronic maxillary sinusitis were studied with unenhanced CT before undergoing sinonasal surgery. In 36 patients, the CT scans were reviewed retrospectively to ascertain the shape and location of intrasinus calcifications. RESULTS: Calcifications were found in 20 (51%) of 39 patients with fungal sinusitis and in 16 (3%) of 471 patients with nonfungal sinusitis. Direct histopathologic correlation was performed in two of 16 patients with nonfungal sinusitis who had intrasinus calcification. The location of intrasinus calcification was central in 95% of the patients with fungal sinusitis and peripheral in 81% of those with nonfungal sinusitis. Although calcifications with a nodular or linear shape were seen in both fungal and nonfungal sinusitis, fine punctate type calcifications were seen only in those with fungal sinusitis (50%) and round or eggshell type calcifications only in those with nonfungal sinusitis (19%). CONCLUSION: Intrasinus calcifications are different in location and shape between fungal and nonfungal maxillary sinusitis. Although intrasinus calcification is uncommon in nonfungal sinusitis, the CT finding of intrasinus calcification may be helpful for differentiating fungal from nonfungal maxillary sinusitis. (+info)