Clinical evaluation of irreversible compression of ultrasound images using the JPEG algorithm at approximately 9:1. Joint Photographic Expert's Group.
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Algorithms↗
Biomedical subjects
J M Knudsen
Publications and source records attributed to J M Knudsen.
Fracture interpretation using electronic presentation: a comparison.
The purposes of this study were to determine whether (1) fractures are interpreted differently after digitization and electronic presentation; (2) there are differences in accuracy between screen radiographs and electronic presentation; (3) differences in interpretation are a function of monitor resolution; and (4) differences in interpretation between radiographs and electronic images relate to radiological subspecialty. Forty cases with fractures of varying degrees of subtlety and 35 cases without fractures were interpreted. Radiographs were digitized with 2 different systems and displayed on 3 monitors of different spatial resolution. Four radiologists, with varying experience, were asked to decide whether fractures were present, absent, or they were uncertain. Accuracy of interpretation increased with improved electronic image presentation and monitor resolution. The sensitivity, specificity, and accuracy of fracture detection on System A were 63%, 98%, and 78%, respectively. The results were 72%, 98%, and 84% with System B. System C results were 81%, 97%, and 88% with Lumiscan 75, and 82%, 96%, and 88% with Lumiscan 150. Sensitivity, specificity, and accuracy results of the original radiograph interpretation were 89%, 95%, and 92%. Results were significantly different for System A. No significant differences were found for the other systems compared with film radiographs. System A did not have adequate monitors for interpretation of subtle fractures. Systems B and C were capable of displaying even subtle fractures. Our initial results indicate that interpretation with high-quality 1K x 1K monitors is substantially similar to radiograph interpretation.
Adult↗
Pheochromocytoma in an incidentally discovered asymptomatic cystic adrenal mass.
Cystic adrenal lesions can be either cortical or medullary, and distinguishing between these 2 types of lesions may be important in patient management. Pheochromocytomas, which are adrenal medullary neoplasms, typically manifest with hypertension, headaches, palpitations, tachycardia, sweating, and anxiety symptoms; however, 10% to 17% of patients with pheochromocytomas are asymptomatic. We describe a 67-year-old woman with lifelong headaches and recent persistent cough in whom a left cystic adrenal mass was incidentally discovered by computed tomography of the chest. A moderate increase in normetanephrine and total metanephrine values in two 24-hour urine samples suggested a pheochromocytoma. Computed tomography with use of contrast medium revealed ring enhancement of the cyst wall, a finding consistent with an adrenal medullary tumor. This report demonstrates the importance of repeated 24-hour urine samples to determine the metanephrine values together with contrast-enhanced computed tomography in a patient with nonspecific symptoms.
Adrenal Cortex Function Tests↗
Arteriovenous fistula of the thyroid gland associated with spontaneous bleeding from a flow-induced aneurysm of the inferior thyroid artery.
A case of acute, spontaneous cervical hemorrhage caused by a ruptured aneurysm of the inferior thyroid artery is described. This lesion was accompanied by an arteriovenous fistula within the thyroid gland that caused a flow-induced aneurysm. Diagnosis and treatment were successfully performed by selective angiography with endovascular occlusion and embolization. Both diagnostic and therapeutic management are discussed, and the related literature is reviewed. To our knowledge, this is the first reported case of an aneurysm of a thyroid artery in conjunction with an intraparenchymatous arteriovenous fistula of the thyroid gland.
Aged↗
Overview of the Mars Pathfinder mission and assessment of landing site predictions.
Chemical analyses returned by Mars Pathfinder indicate that some rocks may be high in silica, implying differentiated parent materials. Rounded pebbles and cobbles and a possible conglomerate suggest fluvial processes that imply liquid water in equilibrium with the atmosphere and thus a warmer and wetter past. The moment of inertia indicates a central metallic core of 1300 to 2000 kilometers in radius. Composite airborne dust particles appear magnetized by freeze-dried maghemite stain or cement that may have been leached from crustal materials by an active hydrologic cycle. Remote-sensing data at a scale of generally greater than approximately 1 kilometer and an Earth analog correctly predicted a rocky plain safe for landing and roving with a variety of rocks deposited by catastrophic floods that are relatively dust-free.
Atmosphere↗
Magnetic properties experiments on the Mars Pathfinder lander: preliminary results.
Many of the particles currently suspended in the martian atmosphere are magnetic, with an average saturation magnetization of about 4 A. m2/kg (amperes times square meters per kilogram). The particles appear to consist of claylike aggregates stained or cemented with ferric oxide (Fe2O3); at least some of the stain and cement is probably maghemite (gamma-Fe2O3). The presence of the gamma phase would imply that Fe2+ ions leached from the bedrock, passing through a state as free Fe2+ ions dissolved in liquid water. These particles could be a freeze-dried precipitate from ground water poured out on the surface. An alternative is that the magnetic particles are titanomagnetite occurring in palagonite and inherited directly from a basaltic precursor.
Atmosphere↗