Analytic reconstruction of magnetic resonance imaging signal obtained from a periodic encoding field

We have proposed a two-dimensional PERiodic-Linear (PERL) magnetic encoding field geometry B(x,y) = g(y)y cos(q(x)x) and a magnetic resonance imaging pulse sequence which incorporates two fields to image a two-dimensional spin density: a standard linear gradient in the x dimension, and the PERL field. Because of its periodicity, the PERL field produces a signal where the phase of the two dimensions is functionally different. The x dimension is encoded linearly, but the y dimension appears as the argument of a sinusoidal phase term. Thus, the time-domain signal and image spin density are not related by a two-dimensional Fourier transform. They are related by a one-dimensional Fourier transform in the x dimension and a new Bessel function integral transform (the PERL transform) in the y dimension. The inverse of the PERL transform provides a reconstruction algorithm for the y dimension of the spin density from the signal space. To date, the inverse transform has been computed numerically by a Bessel function expansion over its basis functions. This numerical solution used a finite sum to approximate an infinite summation and thus introduced a truncation error. This work analytically determines the basis functions for the PERL transform and incorporates them into the reconstruction algorithm. The improved algorithm is demonstrated by (1) direct comparison between the numerically and analytically computed basis functions, and (2) reconstruction of a known spin density. The new solution for the basis functions also lends proof of the system function for the PERL transform under specific conditions.     

Current therapy of retrolental fibroplasia. Retinopathy of prematurity

Retrolental fibroplasia, frequently referred to now as the "retinopathy of prematurity," has shown an increased incidence in recent years. This is apparently due to advances in neonatal care, which have resulted in a four- to five-fold improvement in the survival of the extremely low birthweight infants and it is these infants who are at the highest risk of developing retrolental fibroplasia. The use of large supplements of vitamin E, a known antioxidant, is discussed along with other forms of therapy.     

Anterior cruciate reconstruction using a Dacron ligament prosthesis. A long-term study.

A single-center prospective study is presented on 35 patients who underwent anterior cruciate ligament reconstruction using a Dacron ligament prosthesis. All of the reconstructions were performed by the same surgeon, using the same technique. All of the patients had a history of symptomatic chronic ACL insufficiency. The mean follow-up interval for all patients was 50 months. There was an overall failure rate of 37.1% (13 patients), based on the presence of at least one of the following criteria: the presence of a pivot shift; a 2+ or greater anterior drawer or Lachman; instrumented laxity of greater than 3 mm side-to-side translation in 20 degrees of flexion at 89 N; or by arthroscopic documentation. Six of these 13 patients were documented by arthroscopy and 7 were clinical failures. There were 26 patients with only anterior cruciate ligament laxity, and 9 patients with multiple instabilities or failed previous ACL reconstruction ("salvage"). In the group with isolated anterior cruciate ligament insufficiency, the failure rate was 23% (6 patients). In the salvage group, the failure rate was 78% (7 patients). There was a significant improvement in patient performance with respect to clinical laxity, Lysholm scores, and Tegner activity levels at 2 years postoperatively. There has been a subsequent deterioration in the performance of these patients through time.     

The natural history of serous retinal pigment epithelium detachment in patients with age-related macular degeneration

One hundred ten patients with serous detachment of the retinal pigment epithelium (RPE) were reexamined to enhance our knowledge of the natural course of this condition. All patients were greater than 50 years of age, had age-related macular degeneration, and had neither blood, lipid, nor angiographic evidence of a definite choroidal neovascular membrane (NVM) at the time of the initial examination. All patients were followed up for at least six months except for two patients who had developed a choroidal NVM within the first six months of the initial exam. Forty-five of 140 eyes (32%) developed a choroidal NVM within an average of 19.6 months (median, 12 months). This was associated with a final visual acuity of 20/200 or worse (P less than 0.0001). Ophthalmoscopic and angiographic features present at the initial visit which were associated with the development of NVM and poor final visual acuity were: sensory retinal detachment; increased size of PED; hot spot; late filling; notching; and irregular filling. At the most recent examination, 39% of the eyes had a final visual acuity of 20/20 to 20/40, while 24% of the eyes had a final visual acuity of less than or equal to 20/200.     

Distal esophageal ballooning following Heller myotomy

Eccentric ballooning of the distal esophagus was observed radiographically in 11 of 23 patients (48%) who underwent Heller myotomy for achalasia. While, to the authors' knowledge, ballooning at the site of myotomy incision has not been described previously in the radiologic literature, it should be recognized as a normal and frequent postoperative finding. Radiologists should be aware of this finding so that it is not mistaken for postoperative abnormalities following esophagomyotomy or an epiphrenic diverticulum.     

Pulmonary nontuberculous mycobacterial infection: radiologic manifestations.

The nontuberculous mycobacteria (NTMB) are a group of bacteria that can infect the cervical lymph nodes, skin, soft tissues, and lung. Pulmonary NTMB disease is increasing in prevalence and is most commonly caused by Mycobacterium avium-intracellulare or M kansasii. Occasionally, M xenopi, M fortuitum, or M chelonae also causes pulmonary disease. Diagnosis of pulmonary NTMB infection is often difficult because isolation of the organism from sputum or bronchoalveolar lavage fluid can represent airway colonization. The radiologic manifestations of pulmonary NTMB infection are protean and include consolidation, cavitation, fibrosis, nodules, bronchiectasis, and adenopathy. Pulmonary NTMB infection has five distinct clinicoradiologic manifestations: (a) classic infection, (b) nonclassic infection, (c) nodules in asymptomatic patients, (d) infection in patients with achalasia, and (e) infection in immunocompromised patients. Although classic NTMB infection may be indistinguishable from active tuberculosis, it is usually more indolent. The radiologic features of nonclassic NTMB infection are characteristic: bronchiectasis and centrilobular nodules isolated to or most severe in the lingula and middle lobe. In patients with acquired immunodeficiency syndrome, mediastinal or hilar adenopathy is the most common radiographic finding. Knowledge of the full spectrum of clinical and radiologic features of pulmonary NTMB infection is important to facilitate diagnosis and treatment.     

Fibronectin binding to thrombin-stimulated platelets: evidence for fibrin(ogen) independent and dependent pathways

Plasma fibronectin binds in a specific and saturable manner to thrombin- stimulated platelets. gamma-Thrombin stimulated 80% as much fibronectin binding to platelets as alpha-thrombin with conversion of less than or equal to 1% of platelet fibrinogen to fibrin. Afibrinogenemic and normal platelets bound similar quantities of fibronectin in the presence of calcium or magnesium-ethylene glycol tetra-acetic acid (EGTA). These observations indicate that fibronectin can interact with platelets without involvement of fibrin or fibrinogen. Nevertheless, two different effects of fibrin(ogen) on fibronectin binding were observed. First, exogenous fibrinogen inhibited fibronectin binding to thrombin-stimulated platelets. This inhibition was unidirectional, as fibronectin did not inhibit fibrinogen binding to ADP or thrombin- stimulated cells. Second, formaldehyde-fixed cells with surface- associated fibrin bound significant quantities of fibronectin. This interaction required calcium and did not occur on fixed cells with or without surface-bound fibrinogen. A portion of the ligand bound to fixed cells with surface-associated fibrin was modified to form a derivative with a molecular weight identical to that of the fibronectin subunit cross-linked to the alpha-chain of fibrin. This high mol wt derivative was also observed to a variable extent with living cells in the presence of magnesium or calcium but not in the presence of magnesium-EGTA. Thus, fibronectin binds to platelets by at least two mechanisms: (1) a fibrin(ogen)-independent pathway that requires divalent ions and is inhibited by exogenous fibrinogen; and (2) a fibrin-dependent pathway with an absolute calcium requirement. With nonaggregated, thrombin-stimulated platelets, the former pathway appears to predominate.     

New insights on the emergence of cholera in Latin America during 1991: the Peruvian experience

After a century of absence, in late January 1991, Vibrio cholerae invaded the Western Hemisphere by way of Peru. Although a number of theories have been proposed, it is still not understood how that invasion took place. We reviewed the clinical records of persons attending hospital emergency departments in the major coastal cities of Peru from September through January of 1989/1990 and 1990/1991. We identified seven adults suffering from severe, watery diarrhea compatible with a clinical diagnosis of cholera during the four months preceding the cholera outbreak, but none during the previous year. The patients were scattered among five coastal cities along a 1,000 km coastline. We postulate that cholera vibrios, autochthonous to the aquatic environment, were present in multiple coastal locations, and resulted from environmental conditions that existed during an El Nino phenomenon. Once introduced into the coastal communities in concentrations large enough for human infection to occur, cholera spread by the well-known means of contaminated water and food.     

Diamond-Blackfan syndrome: evidence against cell-mediated erythropoietic suppression

The profound anemia of Diamond-Blackfan syndrome (DBS) is due to marrow red cell failure, but the pathogenesis is not understood. Studies by others indicated cell-mediated erythropoietic suppression in this condition. To explore this mechanism further, Ficoll-Hypaque--separated peripheral blood lymphocytes (PBL) from four anemic untreated patients with DBS, or from normals were cocultured with control marrow in vitro and the growth of erythropoietin-responsive stem cell colonies (CFU-E) was dermined. CFU-E numbers obtained from cultures with added normal PBL were not significantly different from the number without PBL. Similarly, CFU-E from cultures with added DBS PBL were not significantly different from the number without PBL (215 versus 220, 229 versus 220 and 84 versus 60, 74 versus 94/10(5) cells, respectively). Mixing marrows from a control and one DBS patient in ratios of 2:1, 1:1, or 1:2 prior to culture failed to disclose a decrease of colony growth. We could not show cellular inhibition of erythropoiesis in these patients with DBS. The mechanism of anemia in this disorder remains an open question.