Visualization and detection-localization on computed tomographic images

These studies investigated observers' ability to detect and locate highly visible liver lesions on computed tomographic (CT) images, manipulating both the lesion's location and polarity (brighter or darker than liver background). Visibility of a lesion is not sufficient to guarantee accurate localization. With clinical images, possible confusions between a lesion and coexisting normal structures (like blood vessels) is a serious constraint on observer performance.

Enhancing and evaluating diagnostic accuracy

Techniques that may enhance diagnostic accuracy in clinical settings were tested in the context of mammography. Statistical information about the relevant features among those visible in a mammogram and about their relative importances in the diagnosis of breast cancer was the basis of two decision aids for radiologists: a checklist that guides the radiologist in assigning a scale value to each significant feature of the images of a particular case, and a computer program that merges those scale values optimally to estimate a probability of malignancy. A test set of approximately 150 proven cases (including normals and benign and malignant lesions) was interpreted by six radiologists, first in their usual manner and later with the decision aids. The enhancing effect of these feature-analytic techniques was analyzed across subsets of cases that were restricted progressively to more and more difficult cases, where difficulty was defined in terms of the radiologists' judgements in the standard reading condition. Accuracy in both standard and enhanced conditions decreased regularly and substantially as case difficulty increased, but differentially, such that the enhancement effect grew regularly and substantially. For the most difficult case sets, the observed increases in accuracy translated into an increase of about 0.15 in sensitivity (true-positive proportion) for a selected specificity (true-negative proportion) of 0.85 or a similar increase in specificity for a selected sensitivity of 0.85. That measured accuracy can depend on case-set difficulty to different degrees for two diagnostic approaches has general implications for evaluation in clinical medicine. Comparative, as well as absolute, assessments of diagnostic performances--for example, of alternative imaging techniques--may be distorted by inadequate treatments of this experimental variable. Subset analysis, as defined and illustrated here, can be useful in alleviating the problem.

Production and characterization of improved liposomes containing radiographic contrast media

The authors have investigated liposomes prepared by the reverse-phase evaporation method (REVs) and a modification of this technique that employs a microemulsifier (MREVs), for the delivery of radiographic contrast media (RCM) to the liver and spleen. The modification entailed substituting a Microfluidizer (Microfluidics Inc., Newton, MA) for the sonication step of the REV technique. The MREV procedure is amenable to large-scale production and continuous-flow operation and yields products with high RCM encapsulation. Efficiently entrapped are ionic, high-osmolar diatrizoate (24.38 +/- 2.62% versus 8.35 +/- 0.55%; MREV versus REV), and nonionic, low osmolar Iotrolan (Schering AG, Berlin, FRG) (24.84 +/- 2.13% versus 7.25 +/- 1.19%) RCM with iodine-to-lipid ratio of 1.5:1. The MREV procedure, therefore, has practical advantages over the REV method. High liver and spleen uptakes of Iotrolan-containing vesicles were noted in normal rats. The diatrizoate MREVs lost their contents on contact with serum, resulting in urinary excretion of this agent. Computed tomography values of splenic and hepatic sections, 1 hour after intravenous injection of Iotrolan MREV (500 mgI/kg), are 0.78, and 0.08 Hounsfield Units (HU)/mgI/kg, respectively (versus 0.01, and 0.006 HU/mgI/kg for free Iotrolan).

Biodistribution and clearance of contrast-carrying MREV liposomes

Contrast-carrying liposomes (CCLs) have been shown to increase the attenuation coefficient of the liver and spleen during computed tomographic (CT) imaging. A modification of the reverse-phase evaporation preparative technique ("MREV") led to production of CCLs that entrap contrast media efficiently. After intravenous injection, MREVs are phagocytized by the Kupffer cells of the liver and the macrophages of the spleen. The biodistribution and clearance of MREVs were studied to evaluate their potential for clinical use, MREVs carrying iodine-125-iotrolan were administered intravenously to 12 rats at doses of 400 mg lipid (containing 400 mg iodine) per kilogram body weight. Pairs of rats were anesthetized and scanned at 3 hours, and 1, 7, 14, 27 and 48 days; CT attenuation values of liver, spleen, blood, kidneys and bladder were measured. Immediately following CT, the rats were killed and tissue specimens were radioassayed. Maximum iodine content in liver and spleen was reached at one day and sustained at high levels for seven days. Biologic removal half-time of the agent in both the liver and spleen was six days. Maximum CT enhancements over baseline were observed at 24 hours and reached 210 delta HU in the liver and 880 delta HU in the spleen per gram iodine injected per kilogram body weight. It is concluded that MREVs have appropriate imaging characteristics, biodistribution, and clearance to be effective CT contrast agents.

Chronic osteomyelitis: the relative roles of scintigrams, plain radiographs, and transmission computed tomography

We evaluated the relative contribution of transmission computed tomograms (CT), plain radiographs, and bone/gallium scans in the diagnosis of 27 patients with suspected active chronic osteomyelitis. All patients were imaged with all modalities and had surgical proof of the presence or absence of disease. At surgery, osteomyelitis was shown to be active in 20 patients, 15 of whom had sequestra, and inactive in the remaining seven. CT depicted all 15 sequestra, but was falsely positive in three patients, all of whom had bone remodeling only and had negative bone/gallium scintiscans. Plain radiographs had a limited value; they detected sequestra, which was the only findings to indicate the presence of active disease, in 5 patients out of the 15 with surgical proof thereof. The authors conclude that, considering the shortcoming of other modalities with regard to depicting sequestra, scintigraphy is helpful in confirming the presence or absence of active disease and therefore in preventing unnecessary surgery.

Contrast-carrying liposomes. Current status

The goal of recent research has been to encapsulate standard, water-soluble radiographic contrast media (RCM) into liposomes, in order to direct them to reticuloendothelial tissues. Toward this end several varieties of contrast-carrying liposomes (CCLs) have been prepared. Each of these has proven effective in opacifying the liver and spleen of animals on computed tomography (CT). The suitability of two new encapsulation techniques: (1) Microemulsification (MELs), and (2) Dehydration Rehydration Vesicles (DRVs), for CCL production has been explored recently. Each of these two new preparative techniques were valuable in the effort to "scale-up" the CCL production process, leading to "pharmaceutically acceptable" preparation.

Size discrimination in computed tomographic images. Effects of feature contrast and display window

Studies show that features on computed tomographic (CT) images in clinical formats become less detectable when the images are produced with wider CT display windows. We studied the effects of feature contrast and the display window on observer performance in higher-order tasks that involved discriminating small size differences between features on CT images. The features to be discriminated were pairs of disks (9.0 or 9.5 mm in diameter) superimposed on CT images of water phantoms. Sets of image stimuli for two different types of size-discrimination tasks were generated with various CT contrasts specified for the superimposed features and were produced on film transparencies with display windows ranging from 90 to 2880 Hounsfield units (HU) in width. Observers' performance improved with increasing CT contrast in both size discrimination tasks. Unlike performance in feature-detection tasks, however, size discrimination was unaffected by changing the CT display window over a factor of 16 (from 90 to 1440 HU). Performance fell only at the widest display window (2880 HU), for which CT noise was essentially invisible. These results suggest that the effect of changing the CT display window may depend on the spatial frequency content of image information required for a given task.

Evaluation of the dehydration-rehydration method for production of contrast-carrying liposomes

We measured the amounts of three types of radiographic contrast media (RCM) that could be entrapped in liposomes prepared by the dehydration-rehydration vesicle (DRV) technique. To make DRVs, one initially makes water-containing, small unilamellar vesicles, adds contrast media and lyophilizes the mixture. Upon rehydration, the DRVs re-form, passively entrapping RCM. Diatrizoate, iohexol and iotrolan proved to be entrappable in similar amounts (diatrizoate was best), but all of these amounts were less than for other small molecules, such as carboxyfluorescein (P less than 0.05). Entrapment was directly proportional to lipid concentration (r = 0.76; P less than 0.002), and inversely related to iodine concentration (r = 0.86; P less than 0.002). Under ideal conditions with neutral lipids, 19.45 +/- 9.9% of diatrizoate was entrapped, corresponding to 1.05 +/- 0.50 g I per g lipid. These values are close to those achievable for large unilamellar vesicles. Use of an automated mixing device (the Microfluidizer) in place of sonication, facilitated production of large liposome batches and improved entrapment (P less than 0.05). Computed tomography (CT) scans of rats showed 30 and 218 HU of liver and spleen enhancement, respectively, per g I/kg injected DRVs. These studies showed this method (possible augmented by the Microfluidizer) allows efficient production of contrast-carrying liposomes.

Analysis of the tethered-bowel sign on abdominal CT as a predictor of malignant ascites

The value of the "tethered-bowel sign" as a predictor of the nature of intraabdominal fluid was assessed. In the presence of moderate amounts of abdominal fluid, the sign was said to be positive if small or large bowel loops were not seen to float freely on computed tomographic (CT) images, and did not make contact with the anterior abdominal wall. A positive sign was significantly associated with the presence of malignant cells in the fluid (P less than 0.005). When equivocal cases were excluded, the sign had a sensitivity of 85%, a specificity of 93%, and an accuracy of 88%. In the study population (64% prevalence of malignant fluid), the sign had a positive predictive value of 96%, but a negative predictive value of only 78%. When equivocal cases were included, the sensitivity dropped to 69%, the specificity to 78%, and the accuracy to 72%. It is concluded that CT evidence of tethered-bowel loops strongly suggests a malignant cause of ascitic fluid.

Gaining insight: improved images enhance understanding

The past several decades have witnessed dramatic advances in the technology of image acquisition and display. There have been some parallel but less spectacular advances in understanding human acquisition and analysis of visual information. For the first time, imaging devices are available that allow the operator to determine the brightness relationships between normal and pathologic structures. For the first time too, it is becoming possible for the community of scientists interested in medical imaging to marry knowledge of human observer performance with the capabilities of the modern display devices to permit maximum information extraction from medical images.

Modern imaging of the masseter muscle: normal anatomy and pathosis on CT and MRI

Tremendous advances in diagnostic imaging technology have produced computed tomography (CT) and magnetic resonance (MR) imaging--new ways to depict the normal anatomy and pathosis of the masseter muscle. This article reviews the masseter muscle's normal appearance on CT and MR images and demonstrates the clarity with which CT, in particular, is able to depict soft tissue lesions and neighboring bony involvement. Analysis of the strengths, weaknesses, and availability of these new techniques leads to the conclusion that CT is currently the test of choice for imaging masseteric lesions but that MR shows greater promise for the future.

Characterization of liposomes containing iodine-125-labeled radiographic contrast agents

Multilamellar liposomes were prepared containing either iodine-125-labeled (125I) diatrizoate or 125-I labeled iotrol in their aqueous phase. The in vitro permeabilities of liposomes containing both contrast agents were measured in the presence of saline and serum at 37 degrees C. Two different phospholipid compositions were studied: phosphatidylcholine/cholesterol/stearylamine (PC/C/S, 8: 1:1 molar ratio) and distearoylphosphatidylcholine/sphingomyelin (DSPC/SM, 5:2 mole ratio). In saline, similar permeabilities were observed for the four phospholipid-contrast agent combinations. In serum, however, leakage of 125I activity was 2 to 3 times greater from PC/C/S liposomes than from vesicles composed of DSPC/SM. When PC/C/S liposomes that contained 125I-diatrizoate were injected into rats, the clearance half-times for 125I activity from the liver, spleen, and whole body were 4.4 hours, 4.5 hours, and 2.8 hours, respectively. Liposomes composed of DSPC/SM cleared at a significantly slower rate from the liver, spleen, and whole body with half-times of 24.0 hours, 18.4 hours, and 17.2 hours observed from these tissues, respectively.

The production and evaluation of contrast-carrying liposomes made with an automatic high-pressure system

An automatic, high-pressure system (Microfluidizer) has been found useful for producing contrast-carrying liposomes on an industrial scale. The goal of this investigation was to determine the feasibility of using this new microemulsification process to manufacture contrast-carrying microemulsified liposomes (MELs). Seven contrast media (three ionic, four nonionic) were encapsulated into the MELs. Light and electron microscopy, light scattering, radioisotope, and CT scan techniques were used to characterize these MELs, and the contrast entrapments among the studied media were compared. The contrast-carrying MELs had good properties for imaging normal reticuloendothelial tissues, selectively. They had a narrow size range (0.1-3.0 micron), a single bilayer wall, high liver and spleen upake, and low leakage rates. The nonionic media were significantly more effectively entrapped in the MELs than the ionic media (P less than .05). The iodine-to-lipid weight ratio was about 1:16 for ionic media and 1:4 for nonionic media. Physical properties of the contrast media such as osmotic pressure and charge appeared to affect contrast entrapment. It was concluded that the microemulsification process is a useful system for producing contrast-carrying liposomes continuously, on a large scale and in a reproducible manner.

Organ envelopment in lymphoma visualised by computed tomography

In 12 patients computed tomography revealed an unusual pattern of lymphomatous growth resulting in envelopment or engulfment of an organ. The kidneys were involved in eight cases, and the mediastinum and pericardium, oesophagus, stomach and rectosigmoid colon, and psoas muscle in one case each. Ten patients had non-Hodgkin's lymphoma and two had Hodgkin's disease; in every case, lymphomatous masses surrounded but did not destroy the affected tissues. The potential for both Hodgkin's and non-Hodgkin's lymphomas to enwrap both renal and non-renal tissues has not previously been emphasised.

Incidentally discovered mass of the adrenal gland

Increasing numbers of asymptomatic masses of the adrenal gland are being discovered by high resolution computed tomography (CT) scanning. The significance of these masses and the question of further evaluation or treatment, or both, have posed a dilemma. From 1976 to 1983, an incidental finding of adrenal gland mass was identified in 88 patients undergoing abdominal CT scanning for unrelated problems. Adrenelectomy was performed upon 23 patients (26 per cent), including three adenomas (2.5, 3.0 and 6.5 centimeters), five carcinomas of the adrenal gland (6 to 20 centimeters), two hyperplasias and three adenocarcinomas of unknown origin. Thirty-eight (43 per cent) of the nonfunctioning masses were observed with repeat scans for an average of 25.1 months (three to 60 months), revealing no change in size. Twenty-seven patients (31 per cent) were lost to follow-up study. Silent primary (nonmetastatic) masses 3.5 centimeters or less manifested benign behavior without exception. Based upon these data, we conclude that all solid metabolically inactive lesions in the adrenal glands greater than 3.5 centimeters on CT abdominal scan deserve exploration. Lesions less than 3.5 centimeters may be safely followed with serial CT scans.

Hepatocellular carcinoma presenting as primary extrahepatic mass on CT

Seven cases of hepatocellular carcinoma (hepatoma) (HCC) presenting as primary extrahepatic masses on CT are reported. All cases were diagnosed at the time of percutaneous biopsy, surgical resection, or autopsy. In none of the cases was the final diagnosis of HCC prospectively suspected on the basis of clinical and radiologic findings. Although three of the patients were at higher risk for development of HCC because of their medical histories, the absence of an elevated serum alpha-fetoprotein level and the extrahepatic location of the masses by CT suggested other disease. This variable pattern of radiologic presentation of HCC should be kept in mind during the evaluation of patients with suspected HCC, or when the findings on abdominal/pelvic CT of mass and presumed hepatic metastases are at variance with the clinical presentation.

CT diagnosis of adrenal abnormalities in patients with primary non-adrenal malignancies

Fifty-seven patients with primary non-adrenal malignancy were found to have unsuspected adrenal abnormality on CT. In 33, comparison of histopathologic findings and/or the patients' hospital course or follow-up lead to the diagnosis of adrenal metastases (23), benign non-functioning adenomas (7), metastasis with hyperplasia (1), benign hyperplasia (1), and fatty infiltration (1). The analysis of CT findings indicated that: I) A heterogeneous adrenal mass showing contrast enhancement was always metastatic, II) Nonfunctioning adenomas were always 3 cm or smaller in diameter, III) Bilateral adrenal masses and growth of adrenal mass on follow-up CT or regression on treatment indicated metastases, and IV) metastatic disease could not be excluded purely on the basis of the size of the adrenal mass.

Malignant mesothelioma with brain metastases

Although malignant mesothelioma is known to spread hematogenously, brain metastases are rare. In the patient presented herein, multiple unilateral symptomatic central nervous system metastases developed that were diagnosed by computed tomography and documented at autopsy. Since malignant mesothelioma is occurring more frequently in the population at risk (asbestos workers), this complication may be observed more commonly in the future.

Computed tomography of the hindfoot with rheumatoid arthritis

We are performing direct, coronally oriented computed tomographic (CT) scans of the subtalar joint in patients with rheumatoid arthritis. To date, 16 examinations have been performed in 14 patients, 5 of whom were scheduled to undergo subtalar arthrodesis. Scans were 4-7-mm thick and spanned the length of the subtalar joint. CT scans depicted and localized subtalar abnormalities clearly and precisely. On CT scans, patients showed a characteristic constellation of abnormalities including: soft tissue swelling, cartilage space narrowing, bony erosions, and a pes planovalgus alignment abnormality (consisting of increased heel valgus angulation, and a tendency toward flattening of the sustentaculum tali, and medial and downward slippage of the talar head). The clarity of the CT images facilitated the surgeon's pre- and postoperative evaluation. In particular, it was easy to plan the correction of the valgus deformity, anticipate any special requirements for reinforcing the articular surfaces, and assess the results of surgery. We conclude that coronal CT scans clearly demonstrate abnormalities and help the surgeon evaluate the rheumatoid hindfoot.