Volume detection threshold: quantitative comparison of computed radiography and screen-film radiography in detection of pneumothoraces in an animal model that simulates the neonate.

PURPOSE: To quantitatively compare computed radiography (CR) and screen-film radiography (SFR) in the detection of pneumothorax in an animal model that simulates the neonate. MATERIALS AND METHODS: Three rabbits underwent placement of 5-F catheters in the right pleural space. Eight CR and eight SFR images were obtained. Volume-controlled pneumothorax was induced by incrementally injecting 4 cm3 of air (24 cm3 total) and four CR and four SFR images were obtained after each injection. Four radiologists blindly viewed the images twice (eight readings per image, 1,600 total observations). A dichotomous yes-no score for the presence of pneumothorax was used to calculate the volume detection threshold (VDT), defined as the air volume at which 50% of the pneumothoraces can be detected. The authors plotted the likelihood of a pneumothorax against the air volume by using the confidence indicator. RESULTS: Intraobserver VDT values for CR and SFR were not significantly different. CONCLUSION: CR is as accurate as SFR in the detection of pneumothorax in this quantitative animal model.

Rabbit pneumothorax. Feasibility of an animal model to simulate neonatal pneumothorax.

RATIONALE AND OBJECTIVES: The feasibility of developing an animal model to simulate radiographic features of neonatal pneumothorax was investigated, and supine computed radiography (CR) and film-screen radiography (FS) images were compared. METHODS: 5-Fr pigtail catheters were inserted into the right pleural space of three New Zealand white rabbits. Two CR and two FS supine images were obtained using identical technique. After serial 4-mL injections of air, one CR and one FS supine image were obtained. The images were masked and randomized, and four radiologists reviewed the images for typical signs of pneumothorax. Chest computed tomography (CT) was performed before the injection of any air and after completion of the study. RESULTS: At zero-mL air volume, radiologists did not perceive a pneumothorax. As the air volume increased, the number of signs of a pneumothorax increased; there was no significant difference between CR and FS in the number of signs of pneumothorax detected at any volume. Chest CT confirmed that there was no unexplained air leak. The volume of air injected correlated with the calculated volume from the CT. CONCLUSIONS: This induced, volume-controlled, animal model simulated the supine radiographic features of neonatal pneumothorax.

Prospective study of magnetic resonance imaging and SPECT bone scans in renal allograft recipients: evidence for a self-limited subclinical abnormality of the hip.

We recently reported that typical abnormalities of avascular necrosis (AVN) in magnetic resonance images (MRI) of the hips of asymptomatic renal transplant recipients whose plain radiographs are normal may improve spontaneously and even disappear completely. We present the results of serial bone scans, most of which were performed with single-photon emission computed tomography obtained over periods as long as 24 mo after transplantation in 72 of these patients. Three paired imaging studies (i.e., MR and bone scan performed within 30 days of each other) were available for each of these patients. In three patients, both the MR images and the bone scans showed changes consistent with bilateral AVN within 4 mo after transplantation. All three patients developed hip pain which was bilateral in two and unilateral in one. Two patients (three hips) required surgical intervention at which time AVN was found on pathologic examination of all three hips. None of the remaining 69 patients developed hip pain during the study. However, in nine patients whose MR studies were consistently normal, at least one bone scan was abnormal (13 hips). The presence of AVN was pathologically confirmed in each of the hips subjected to surgery. Where the imaging findings were identical to those in the asymptomatic patients as well as those in whom the imaging abnormality regressed, we suggest that the subclinical imaging abnormalities represent mild AVN, which is reversible in some cases. Since the process was identified in 10 hips by MRI and in 13 hips by bone scan, both studies are needed to detect subclinical AVN. This may be important if treatment of subclinical disease is clearly shown to prevent progression to symptomatic AVN.

Apparent avascular necrosis of the hip: appearance and spontaneous resolution of MR findings in renal allograft recipients.

The sensitivity of magnetic resonance (MR) imaging in the detection of avascular necrosis (AVN) of the hip and natural history of the MR findings were determined prospectively in renal allograft recipients, a group at risk for development of the disease. One hundred four patients were studied up to 24 months after transplantation. In 25 hips in 14 patients, MR findings were consistent with AVN. Pain developed in seven hips in four patients; in each hip, the MR images showed abnormality before the onset of symptoms. Plain radiographs showed abnormality in all hips that became painful; however, the plain radiographs of 17 of 18 asymptomatic hips in which MR imaging showed evidence of AVN showed no abnormality over a mean follow-up period of 16 months. All MR lesions in the symptomatic hips were larger than those in the asymptomatic cohort. MR lesions in seven hips (in five asymptomatic patients) regressed in size; in six hips, the MR images returned to normal. The findings suggest that some patients with MR evidence of AVN of the hip have spontaneous improvement.

Pathways to improved radiologic research. An NIH workshop.

In summary, the workshop recommended two years of research training as being essential for radiologists to acquire the skills and knowledge necessary to begin a successful research career in today's funding and academic environment. Many pathways can combine two years of research training and provide fulfillment of existing requirements to achieve specialty certification and subspecialty credentialing. Departments of radiology supporting the beginning qualified investigator should allow him or her approximately 75% research time for the first three years of the academic appointment. Departmental research time accorded faculty members may best be concentrated on a few individuals, providing them sufficient time to be competitive for peer-reviewed grants and enabling research advances to provide a solid foundation for the future of radiologic imaging.

Duplex Doppler US of renal allografts: causes of elevated resistive index.

The authors retrospectively investigated the utility of the resistive index (RI) in evaluating the major causes of renal allograft dysfunction. Three hundred fourteen duplex US studies in 162 patients with 150 episodes of renal allograft dysfunction within a 17-month period were reviewed. Histologic findings were available in 69 cases. Three patients had hyperacute rejection with a mean RI of 0.85 +/- 0.049. There were 37 episodes of acute rejection (mean RI, 0.76 +/- 0.054) and 22 instances of chronic rejection (mean RI, 0.71 +/- 0.065). Ureteral obstruction (nine cases; mean RI, 0.72 +/- 0.026) was the only cause of allograft dysfunction other than rejection with a mean RI greater than 0.70. Mean RI values associated with rejection were significantly elevated above those in the 88 cases of dysfunction without rejection (mean, 0.64 +/- 0.064) and in baseline examinations (mean, 0.63 +/- 0.066). The results identified two causes of increased RI values in addition to acute rejection: chronic rejection and ureteral obstruction.

Cranial MR imaging in neurofibromatosis.

Cranial MR images of 53 patients with neurofibromatosis were reviewed to determine the nature, extent, and number of intracranial abnormalities present. All patients studied met tentative definitions established for the diagnosis of neurofibromatosis. Twenty-three were scanned for evaluation of known CNS of cranial nerve involvement; the remainder were neurologically asymptomatic patients without suspected lesions referred for screening. Single lesions were noted in 32 patients. Multiple lesions were identified in 14 patients. Seven had normal scans. In 23 patients small focal areas of increased signal on T2-weighted scans within the brain were though to represent heterotopias. Eight patients had chiasmal gliomas and two had optic nerve gliomas. Nine patients had parenchymal gliomas, two had ischemic changes, and one had a colloid cyst. Extraaxial lesions included acoustic neuromas (five patients), meningiomas (four), trigeminal neurofibromas (one), and dysplasia of a sphenoid wing (two). Of the 30 asymptomatic patients referred for screening, lesions were found in 23. MR was found to be an excellent method of imaging known disease and of detecting lesions in asymptomatic patients. Because of the large number of asymptomatic lesions detected in this population, a screening MR study is recommended in patients with neurofibromatosis.

Gd-enhanced MR imaging of acute and chronic experimental demyelinating lesions.

Experimental allergic encephalomyelitis, a demyelinating disease with marked similarity to multiple sclerosis, was produced in two of 12 dogs. All dogs were studied with serial MR imaging. T1- and T2-weighted MR images were obtained both before and after IV Gd-DTPA. Multiple, new periventricular white matter demyelinating lesions were observed after each clinical episode of the disease. Like multiple sclerosis, the acute lesions of experimental allergic encephalomyelitis on T2-weighted MR images were indistinguishable from the older, more chronic lesions. However, after Gd-DTPA, there was bright paramagnetic enhancement of the acute lesions and, in one animal, no enhancement of the chronic lesions on T1-weighted MR images. At necropsy, the differences in the MR paramagnetic enhancement correlated well with the relative histologic age of the demyelinating lesions. Our results suggest that MR with Gd-DTPA may be used to differentiate acute, active demyelinating lesions from the more chronic, inactive lesions in this animal model.

In vitro study of high-pressure catheters and various contrast agents.

The versatility of angiography has been expanded by the introduction of low-osmolality contrast agents; high-pressure, high-flow catheters with small outer diameters; and the use of contrast agents with low iodine concentrations. These changes have resulted in the need for a review of the physical factors that influence the flow of contrast agents through flush catheters. Various contrast agents were injected through several types of high-pressure, high-flow catheters with small outer diameters, and the flow rates were measured. Great differences in the viscosities of contrast agents resulted in proportionately smaller differences in maximum flow rates, and warming the contrast agent from room to body temperature had little effect on the maximum flow rate, except for the most viscous contrast agents. The maximum flow rates of the new low-osmolality contrast agents did not differ significantly from those of conventional ionic contrast agents of similar iodine concentration. With unheated contrast agents, iodine delivery was more rapid for contrast agents with iodine concentrations of 280-300 mg/mL.

Fibrinolytic therapy.

The state of the art of fibrinolytic therapy is constantly changing; perhaps no other area of medicine is developing as rapidly. This paper presents the status of fibrinolytic therapy from the authors' viewpoint. Many statements are controversial. It is possible to find divergent opinions expressed by experts on almost any aspect of fibrinolysis. Objective data are rapidly accumulating, but because new substances continue to be developed, the present and future statuses of fibrinolysis remain unclear. The current results of fibrinolytic therapy are excellent but will be dwarfed by the effects of new compounds and techniques in the near future. Continued developments in this field will have a major impact on improved health care delivery.

Magnetic resonance imaging of extremity masses.

Twenty-seven adults with extremity masses were examined by magnetic resonance imaging (MRI). In 26/27 cases, computed tomography (CT) scans were available for comparison. Imaging with multiple pulse sequences is necessary to optimize diagnosis by MRI. Advantages of MRI include direct sagittal and coronal imaging, demonstration of vessels without contrast and superior soft tissue contrast. CT better demonstrates cortical destruction and small calcifications, which may be important in some cases. For noncalcified masses without bone involvement, MRI is equivalent or superior to CT. In those cases with calcification or bone involvement, MRI plays a role complementary to CT.

Intracoronary administration of streptokinase in a canine model. Disturbance in thromboxane A2-prostacyclin balance.

The potential impact of local intracoronary infusion of streptokinase (SK) on vascular prostaglandin synthetic pathways was studied in a canine model. Control animals (n = 10) underwent left coronary artery (LCA) infusion of 50,000 units SK for 90 minutes; experimental animals (n = 10) underwent LCA infusion of normal saline. Plasma samples for radioimmunoassay (RIA) of prostacyclin (PGI-2) and thromboxane (TXA-2) were obtained from the coronary sinus (CS) as follows: one sample preinfusion, six samples during infusion, and three samples postinfusion in each animal. Comparisons between control and experimental plasma levels of PGI-2 and TXA-2 were made for each sampling time. The PGI-2 levels remained at or below the lower limits of detectability by RIA (the most sensitive assay available) in both control and experimental animals. TXA-2 levels were higher in experimental than in control animals at all sampling times, with the most significant differences occurring in samples 3 (after 30 minutes of infusion, .001 less than P less than .01), 4 (after 45 minutes of infusion, .05 less than P less than .10), and 5 (after 60 minutes of infusion, .02 less than P less than .05). We suggest (1) it is unlikely that any of the beneficial effects of coronary streptokinase infusions are PGI-2-mediated, (2) that the TXA-2 increases in our model may represent a pathophysiologic-biochemical correlate of previously identified morphologic evidence of endothelial damage in animals infused with fibrinolytic agents, and (3) that our findings may indicate that fibrinolytic infusions produce competing effects: lysis of thrombi and endothelial injury with TXA-2 production.(ABSTRACT TRUNCATED AT 250 WORDS)

Renal vascular hypertension. Surgery vs. dilation.

The blood pressure response to surgery or percutaneous transluminal angioplasty (PTA) was determined an average of 3 years after treatment. In atherosclerotic disease, 85% of patients benefited. Furthermore, the extremely low overall cure rate of 6% (4/67) suggests that renal artery stenosis due to atherosclerosis is rarely a sole cause of hypertension, but more likely is an atherosclerotic complication of essential hypertension that develops in patients who are cigarette smokers. In fibrodysplastic disease both treatments were likely to improve the blood pressure. However, surgery resulted in a 41% rate of loss of the operated kidney. The response to PTA or surgery is strongly influenced by the etiology of the lesion being treated.

Experimental laser-assisted end-to-side microvascular anastomosis.

The authors present a new technique of end-to-side microvascular anastomosis in a rat carotid artery model, employing a milliwatt CO2 laser. Both carotid arteries were isolated and approximated in an end-to-side fashion by the placement of four 10-0 nylon stay sutures. The milliwatt CO2 laser was used to effect vessel anastomosis between the sutures, using 70-100 mW of power. Animals were killed 8 weeks postoperatively. Angiography of each anastomosis was performed in all animals. All anastomoses were then harvested, and submitted for histological analysis. Anastomotic patency was 100%, both intraoperatively and angiographically. There was no evidence of intravascular thrombus, anastomotic stenosis, or pseudoaneurysm formation. Early in the experiment, some anastomoses showed localized dilatation at the anastomotic site. The histologic changes at the anastomotic site are described. Laser-assisted microvascular anastomosis is a feasible technique, and a potential alternative to conventional suture techniques.

Gated MR imaging of left atrial myxomas.

Two cases of left atrial myxoma were evaluated with magnetic resonance (MR) imaging. In both cases, the myxoma was clearly defined as to its location, origin, and size. In one case, the myxoma prolapsed through the mitral valve. Our study indicates that MR imaging is valuable in the diagnosis of myxomas.

Ethanol thrombotherapy of esophageal varices: further experience.

Fifty patients with liver cirrhosis (13 Child class B, 37 class C) were treated for variceal hemorrhage during a 3-year period using the transhepatic selective catheterization and injection of absolute ethanol. Technical failure of the procedure was encountered in 13 instances. The causes were the presence of massive ascites and rigidly contracted liver, cavernous transformation of the main portal vein, and severe coagulopathy. Of the 13 failures, 12 were in Child class C and one in class B. Of 37 initially successfully treated patients, 13 rebled subsequently. Nine of these were Child class C and four were class B. Rebleeding was fatal in five of nine class C patients. Rebleeding was due to recanalization of previously thrombosed access channel in two of 13 patients. Nine patients died, despite successful thrombosis of varices, due to underlying medical conditions. Fifteen patients survived 6 months or more after initial thrombosis without rebleeding. Child class B patients are better candidates for this treatment technique because more favorable treatment results are expected in them. Child class C patients with massive ascites and severely contracted and rigid liver pose a significant technical challenge, but in about one-third, successful control of variceal bleeding can be achieved. Most of those who survived more than 6 months showed varying degrees of improvement in clinical signs and symptoms.

Cardiopulmonary effects of volume expansion in man: radiographic manifestations.

Cardiovascular and humoral responses to extremes of sodium intake (10-1500 mEq/day) were studied. Chest radiographs of eight normal men were obtained to measure changes in heart volume and central vascular structures. Echocardiographic measurements of cardiac chamber dimensions were also obtained. Sodium loading resulted in a 16-mm-Hg increase in mean arterial pressure and increases in cardiac output, stroke volume, left ventricular end-diastolic volume, and all radiographically determined cardiac dimensions. There was direct correlation between the radiographic cardiac dimensions and left ventricular end-diastolic volume. There was no echocardiographic evidence of pericardial fluid. After sodium loading, there was enlargement of the superior vena cava, innominate veins, azygos vein, pulmonary vessels, and the aortic knob. Small pleural effusions were commonly seen. Volume expansion may cause radiographic changes that may mimic those associated with congestive heart failure. This may particularly be the case in patients with renal failure, those receiving dialysis treatment, or patients receiving large volumes of intravenous fluids.

Influence of cardiac function on the quality of intravenous digital subtraction arteriograms.

In a retrospective comparison between 22 pairs of matched intravenous digital subtraction angiogram (DSA) images, five angiographers made independent determinations as to which one of each pair was superior in image quality (110 image comparisons). Matched pairs were identical for anatomic region filmed, catheter position during injection, amount of contrast material injected, injection rate, and iodine concentration of the contrast material. Each pair consisted of images from one patient with a normal (less than 1 S.D. above the mean) sodium dehydrocholate circulation time and images from one patient with a prolonged (greater than 1 S.D. above the mean) circulation time. In 85 of the 110 instances (77.3%) an image judged superior in quality to its matched counterpart derived from a DSA exam in a patient with normal circulation time; images from the exam with prolonged circulation time were judged equal in quality to the ones with the normal circulation time in 14 comparisons (12.3%); in 11 comparisons (10%) the images from the DSA with the prolonged circulation time were judged superior to the ones from the DSA with the normal circulation time. These results show that with statistically significant frequency (P less than 0.001) observers judge intravenous DSA images deriving from patients with normal circulation times superior in quality to those deriving from patients with prolonged circulation times.

Magnetic resonance imaging of lymphomas in children.

Magnetic resonance imaging has been used to evaluate 10 children with lymphomas and was able to identify disease in all 10 cases and monitor response to therapy in all three patients with follow-up studies. It could not distinguish between the different histological types of lymphoma. The image intensity of a diseased spleen in one case was different from that of five other normal spleens in six children with Hodgkins disease. Magnetic resonance imaging compared well with computed tomography and it was especially good at identifying blood vessels.