Single-energy non-contrast hepatic steatosis criteria applied to virtual non-contrast images: is it still highly specific and positively predictive?

AIM: To determine the sensitivity, specificity, and predictive values of single-energy non-contrast hepatic steatosis criteria on dual-energy virtual non-contrast (VNC) images. MATERIALS AND METHODS: Forty-eight computed tomography (CT) examinations, which included single-energy non-contrast (TNC) and contrast-enhanced dual-energy CT angiography (CTA) of the abdomen, were enrolled. VNC images were reconstructed from the CTA. Region of interest (ROI) attenuations were measured in the right and left hepatic lobes, spleen, and aorta on TNC and VNC images. The right and left hepatic lobes were treated as separate samples. Steatosis was diagnosed based on TNC liver attenuation of ≤40 HU or liver attenuation index (LAI) of ≤-10 HU, which are extremely specific and predictive for moderate to severe steatosis. The sensitivity, specificity, and predictive values of VNC images for steatosis were calculated. VNC-TNC deviations were correlated with aortic enhancement and patient water equivalent diameter (PWED). RESULTS: Thirty-two liver ROIs met steatosis criteria based on TNC attenuation; VNC attenuation had sensitivity, specificity, and a positive predictive value of 66.7%, 100%, and 100%, respectively. Twenty-one liver ROIs met steatosis criteria based on TNC LAI. VNC LAI had sensitivity, specificity, and positive predictive values of 61.9%, 90.7%, and 65%, respectively. Hepatic and splenic VNC-TNC deviations did not correlate with one another (R2=0.08), aortic enhancement (R2<0.06) or PWED (R2 <0.09). CONCLUSIONS: Non-contrast hepatic attenuation criteria is extremely specific and positively predictive for moderate to severe steatosis on VNC reconstructions from the arterial phase. Hepatic attenuation performs better than LAI criteria. VNC deviations are independent of aortic enhancement and PWED.

Viewing DICOM-compliant CT images on a desktop personal computer: use of an inexpensive DICOM receive agent and freeware image display applications.

OBJECTIVE: Our objective was to determine the ease of installation and use of relatively inexpensive and free software applications that allow Macintosh users to receive and view CT images from a Digital Imaging and COmmunication in Medicine-compliant imaging network. CONCLUSION: Simple-to-use Macintosh-based options to transfer and view images are readily available and easily installed by users with minimal computer expertise.

Imaging of the liver with helical CT: a survey of scanning techniques.

OBJECTIVE: We conducted a survey of the members of the Society of Computed Body Tomography/Magnetic Resonance to assess current techniques in liver imaging using helical CT. MATERIALS AND METHODS: The survey, which was designed to update earlier surveys from 1987 and 1993, included a questionnaire distributed to 77 members of the Society of Computed Body Tomography/Magnetic Resonance. RESULTS: Forty-nine members responded, representing 28 institutions. In 1993, 19% (5/26) of institutions used helical scanners, compared with 82% (23/28) in 1996. The group of institutions with helical CT served as the focus of this survey. In 1993, 58% of institutions used 1-cm collimation: in 1996, 78% (18/23) used thinner, 7- to 8-mm collimation. In 1987, 41% used power injectors compared with 85% in 1993 and 100% in 1996. In 1996, monophasic injections were used by 96% (22/23) of institutions. In 1993, most institutions used a contrast material injection rate of 1.5-2.0 ml/sec; in 1996, most used a 2.5-3.0 ml/sec injection rate. In 1993, 96% of institutions used 125-150 ml of contrast material; in 1996, 57% (13/23) of institutions used 125-150 ml and 30% of institutions used less than 125 ml of contrast material. A delay time of 21-45 see was used by 83% of institutions in 1993, whereas in 1996, 83% (19/23) of institutions used a longer delay time of 50-80 sec. In 1996, 13% of institutions used an individual scan delay technology and all institutions performed multiphasic scanning of hypervascular lesions. CONCLUSION: The availability of helical CT has changed radiologists' approach to liver imaging. The greatest effects of which are a more widespread use of power injectors, longer delay times, thinner collimation, increased contrast material injection rates, decreased contrast material volumes, and multiphasic scanning.

TNM staging of pancreatic carcinoma using helical CT.

OBJECTIVE: The purpose of this study was to determine the accuracy of helical CT scanning in predicting the stage of carcinoma of the exocrine pancreas using TNM staging guidelines and in predicting resectability of carcinoma of the exocrine pancreas. MATERIALS AND METHODS: Twenty-six patients with proven adenocarcinoma of the pancreas underwent uniphasic or biphasic helical CT scanning. Two observers unaware of the patient's surgical stage evaluated the CT examinations using the TNM system (with specific assessment and description of disease sites). In addition, the two observers rated confidence of nonresectability using a 5-point scale (ranging from 1, definitely resectable, to 5, definitely not resectable). Observer results and preoperative interpretations were compared with surgical findings. RESULTS: Nineteen of 26 patients had nonresectable disease. The combined observer scores showed correct determination of T stage in 77% of patients, of N stage in 58%, and of M stage in 79%. The overall accuracy in determining lack of resectability was 96% and 84% for the two observers. All errors in determining resectable versus nonresectable disease occurred when the observer was not maximally confident of his or her diagnosis. CONCLUSION: Helical CT is an effective screening technique for assessing T and M stages of pancreatic carcinoma. However, helical CT is poor at detecting regional lymph node involvement. In patients with equivocal T-stage findings (such as questionable venous involvement), other studies such as endoscopic sonography may be of value.

Solitary fibrous tumors: a series of lesions, some in unusual sites.

Solitary fibrous tumor (SFT) is a rare neoplasm that, in addition to its classic presentation as a pleural-based mass, can also be encountered in unusual sites. The main difficulty in making the diagnosis of SFTs results from the unfamiliarity with its diverse clinical and pathologic features. This series of SFTs, some with unusual clinicopathologic presentation, included nine women and two men, ranging in age from 28 years to 74 years (five in pleura, one in lung parenchyma, one in breast, and four in mediastinum). The tumors were locally excised in eight cases and were resected along with portions of lung parenchyma in three. A panel of immunohistochemical stains was used to characterize these tumors. They were all vimentin-positive and, with the exception of one case, CD34-positive. Tumors were negative with antibodies directed against cytokeratin, factor VIII-related antigen, S-100 protein, muscle-specific actin, and smooth-muscle actin. Various diagnoses were initially rendered for these clinically and pathologically diverse lesions by the examining pathologists. Awareness of the various gross and microscopic patterns of these tumors, the possibility of occurring in unusual sites, and the use of immunohistochemical stains, particularly CD34, should eliminate most of the difficulties in arriving at a correct diagnosis. One patient died of metastatic breast cancer; all other patients were alive and well with a median follow-up of 17 months.

A phantom study: evaluation of renal artery stenosis using helical CT and 3D reconstructions.

PURPOSE: We studied which set of CT parameters and modeling parameters yielded accurate measurements of three graded artificial renal artery stenoses. METHOD: An acrylic phantom resembling the abdominal aorta and renal arteries was constructed. Stenotic segments had diameters of 1.8, 3.2, and 4.8 mm; nonstenotic segment diameter was 6.3 mm. Helical scans were done using 1 and 3 mm collimation at pitches of 1, 1.5, and 2. 3D renderings were produced and measured. Multifactorial and regression tree analysis were used to determine the accuracy of the 3D renderings. Mean squared error (MSE) was used to compare true diameter with measured diameter. RESULTS: Collimation of 1 mm produced an MSE of 0.55 versus an MSE of 1.35 for 3 mm collimation. Stenosis grade was the next most important parameter in the 1 mm subgroup and viewing direction in the 3 mm collimation subgroup. In the 1 mm subgroup, high and mid grade stenoses had an MSE of 0.52 versus low grade stenosis that had an MSE of 0.61. Pitch was a fourth-order effect. CONCLUSION: Collimation of 1 mm combined with a pitch ratio as high as 2:1 is superior to 3 mm collimation. Shaded surface modeling was the single best choice for rendering 3D data. Stenosis grade interacted strongly with user-controllable parameters.

Helical CT of renal masses: the value of delayed scans.

OBJECTIVE: Routine scanning techniques used for helical CT of the abdomen result in dense cortical opacification of the kidney, whereas the medulla and collecting system are not well opacified, which potentially compromises detection of renal masses. The purpose of this retrospective study was to determine if additional delayed views (taken approximately 2-4 min after the start of injection of contrast material) are necessary for the detection and characterization of renal masses. MATERIALS AND METHODS: Early (60-70 sec after the start of the injection of contrast material) and delayed scans of 40 patients with suspected renal masses were blindly evaluated by two observers. The patients harbored a total of 187 renal masses (including 62 solid masses). Each region of the kidney (upper, middle, and lower pole) was scored for the presence of a mass. Scoring was done as a binary decision and also as a five-point confidence score for receiver operating characteristic analysis. RESULTS: We found 97 regions that contained renal masses and 114 regions that did not. Receiver operating characteristic analysis revealed the observers to have significantly greater confidence in detection of renal masses on the delayed scans. The binary data showed the two observers to have a sensitivity of 97% for delayed scans versus 77% (p = .0002) and 89% (p = .027), respectively, for the early scans. For the first observer, early and delayed scans were of equal specificity, but for the second observer, the delayed scans yielded greater specificity (94% versus 85%, p = .024). On the early scans, both observers were significantly more likely to miss a neoplastic lesion than a nonneoplastic lesion. The less experienced of the two observers also tended to have greater difficulty in characterizing the lesions on the early scans. CONCLUSION: Because of the significant risk of missing a renal mass, especially a neoplasm, on early cortical-phase scans, additional delayed scans appear justified when a renal mass is suspected on the basis of other imaging tests or clinical history.

Assessment of a technology that permits individualized scan delays on helical hepatic CT: a technique to improve efficiency in use of contrast material.

OBJECTIVE: We performed this study to assess the usefulness of a computer automated scan technology (CAST) for individualizing scan delay during helical CT to improve the efficiency of hepatic enhancement. SUBJECTS AND METHODS: We prospectively evaluated 183 patients who were randomized into five groups. Control patients received 100 or 150 ml of contrast material (320 mg I/ml) with a 60-sec delay between contrast injection at 3 ml/sec and scanning. CAST patients received 100, 125, or 150 ml. In our latter groups we used an hepatic enhancement threshold of 50 H over baseline to determine the optimum delay between contrast injection and scanning. For the intergroup comparisons, we measured the liver on baseline and enhanced helical CT scans at the upper, mid, and lower levels of the liver. RESULTS: The mean enhancement in patients who received 150 ml of contrast material was 70.7 +/- 19.4 H for the control group and 81.0 +/- 17.5 H for the CAST group (p < .05). Hepatic enhancement above 50 H was achieved in 84% of the control subjects compared with 100% of CAST subjects; more than 60 H hepatic enhancement was achieved in 73% of control subjects and in 89% of CAST subjects. The use of CAST software with 125-ml contrast doses provided enhancement equivalent to that of control subjects who received 150 ml of contrast material (mean enhancement in CAST subjects, 70.3 +/- 15.4 H). Enhancement above 50 H was reached in 98% of CAST and 84% of control patients. With 100 ml of contrast material, 24% of patients failed to initiate CAST, resulting in enhancement similar to control patients (CAST, 54.2 +/- 11.4 H; controls, 56.9 +/- 15.2 H). CONCLUSION: Using a contrast dose of 150 ml, CAST provided significantly increased hepatic enhancement than that achieved in control subjects with less variability. For equivalent hepatic enhancement, contrast doses could be decreased by 25 ml using CAST technology because it provides individualized scan delays.

MR imaging appearance of the uterus in postmenopausal women receiving tamoxifen therapy for breast cancer: histopathologic correlation.

PURPOSE: To describe the spin-echo and dynamic gadolinium-enhanced magnetic resonance (MR) imaging appearance of the uterus in women receiving tamoxifen. MATERIALS AND METHODS: Thirty-five postmenopausal women with breast carcinoma receiving tamoxifen therapy underwent pelvic MR imaging. T1-weighted, T2-weighted, and dynamic gradient-echo T1-weighted sequences were used. Twenty-seven patients underwent uterine sampling within 3 months of MR imaging. RESULTS: Endometrial width on T2-weighted images ranged from 0.1 to 7.5 cm (mean thickness, 1.1 cm). Two uterine imaging patterns were noted. Patients with pattern 1 findings had homogeneous high signal intensity of the endometrium on T2-weighted images (mean, 0.5 cm) and enhancement of the endometrial-myometrial interface and a signal void in the lumen on gadolinium-enhanced images (18 patients). Patients with pattern 2 findings had heterogeneous endometrial signal intensity on T2-weighted images (mean, 1.8 cm) with enhancement of the endometrial-myometrial interface and latticelike enhancement traversing the endometrial canal on gadolinium-enhanced images (17 patients). Other imaging findings included subendometrial cysts, nabothian cysts, leiomyoma, and adenomyosis. Ten patients with pattern 1 findings had atrophic or proliferative endometria at histopathologic analysis; 12 of the 17 patients with pattern 2 findings had polyps, one of which had a focus of endometrial carcinoma. CONCLUSION: MR imaging of the uterus showed two distinct patterns in women receiving tamoxifen therapy.

Helical (spiral) CT of the upper airway with three-dimensional imaging: technique and clinical assessment.

OBJECTIVE: The purpose of this study was to evaluate the application of helical CT-generated three-dimensional images of the upper airway. MATERIALS AND METHODS: Thirty patients, 10 healthy and 20 with upper-airway disease, were studied with helical CT (5-mm collimation). Overlapping images at 2-mm intervals were retrospectively generated. In the group of healthy patients, two radiologists in independently compared overlapping with nonoverlapping images, ranked confidence in identifying small airway structures on a scale of 1-5, and tabulated the number of images demonstrating these structures. In the 20 patients with disease, three-dimensional (3D) surface models were rendered on an independent workstation and were reviewed by two radiologists and one otolaryngologist for image quality, appreciation of lesion morphology, and ability to judge lesion extent, using a similar scale. A phantom was used to optimize parameters for the 3D reconstructions. RESULTS: Viewing of the retrospectively generated overlapping images increased by 122% the number of images in which laryngeal and hypopharyngeal structures could be identified (p < .01). Image confidence scores for the radiologists averaged 3.3 for nonoverlapping and 4.0 for overlapping (p < .05). Radiologists and otolaryngologist rated the quality of the 3D images equally. The otolaryngologist's assessment of the value of the models for understanding the lesion morphology was 3.5 compared with the radiologists assessment of 2.5; and for judging the lesion extent, the otolaryngologist's assessment was 3.8 compared with 2.7 for the radiologist, a statistical significance of p < .01. CONCLUSION: Helical CT with the application of overlapping images and 3D reconstructions significantly assists the understanding of upper-airway disease.

Pneumatosis intestinalis in adults with AIDS: clinical significance and imaging findings.

OBJECTIVE: The significance of pneumatosis intestinalis in adults with AIDS is unknown. Adults with AIDS are predisposed to pneumatosis intestinalis. The purpose of this study is to determine the clinical significance and to characterize the imaging appearance of this finding in patients with AIDS. MATERIALS AND METHODS: In just over 3 years at our institution, pneumatosis intestinalis in adults with AIDS was detected in six cases. Medical records of those cases were retrospectively analyzed for clinical history, laboratory data, and surgical and pathologic findings. CT scans and abdominal radiographs were analyzed for location and severity of pneumatosis, presence of portal venous gas, pneumoperitoneum, and cystic versus linear gas. RESULTS: Five of the six patients with AIDS-associated pneumatosis intestinalis were managed conservatively or medically without surgical procedures and were discharged from the hospital with resolved or decreasing gastrointestinal complaints. The other patient underwent an exploratory laparotomy because of free intraperitoneal and retroperitoneal air; however, no bowel perforation was found at surgery. CONCLUSION: Pneumatosis intestinalis is a late-stage phenomenon in adult patients with AIDS that characteristically involves the cecum or right colon. Pneumatosis in patients with AIDS may be an indolent abnormality and does not necessarily constitute a surgical emergency or a sign of impending bowel necrosis.

CT angiography.

CT angiography is an exciting yet controversial application of helical (spiral) CT technology. Although many radiologists equate CT angiography with three-dimensional (3D) rendering, we believe that axial images, multiplanar reformatted (MPR) images, and true 3D models all contribute to a better evaluation of the vascular system than was possible with conventional CT. This occurs because helical scans are volumetric and are accomplished rapidly with high levels of circulating contrast material. This article reviews the indications for CT angiography, compares CT angiography with other techniques, and offers a practical methodology for neuroradiologic, thoracic, and abdominal applications of CT angiography.

Helical (spiral) CT of the pancreas and biliary tract.

Helical scanning offers many advantages for the evaluation of benign and malignant pancreatobiliary disease. This article presents these advantages, recommended screening protocols, and guidelines for the use of three-dimensional rendering of the peripancreatic vessels and bile ducts.

Biliary tract: three-dimensional helical CT without cholangiographic contrast material.

Bile duct anatomy depicted with a three-dimensional (3D) model developed with helical computed tomography (CT) data was compared with cholangiographic depiction. The ductal system was completely displayed from all angles in four of six patients, as well as the stricture and length of bile duct between strictures and the bifurcation in five of six cases. 3D rendering can depict preoperative ductal anatomy.

Helical CT of the upper airway: normal and abnormal findings on three-dimensional reconstructed images.

Imaging of the hypopharynx, larynx, and upper airway are effectively achieved with CT and MR imaging. These techniques have proved their diagnostic usefulness in assessing the deep soft tissues not visible with laryngoscopy [1]. However, with axial imaging, large numbers of images often need to be mentally stacked to envision the appearance of the airway. With helical CT, we can create high-quality three-dimensional (3D) reconstructions [2, 3]. Advantages of helical technology include rapid scanning, decreased motion artifact, and minimization of misregistration artifacts. Recent work has suggested a role for multiplanar and 3D reconstructions of helical data for assessing the tracheobronchial tree [3]. The helically derived 3D models illustrate the normal and abnormal findings affecting the airway.

AIDS-associated intussusception in young adults.

We have examined the changing demographics of adult intussusception and implicate human immunodeficiency virus (HIV)- and acquired immune deficiency syndrome (AIDS)-associated gastrointestinal pathology as risk factors for intussusception in young adults. The clinical index of suspicion for intussusception should be raised for an HIV-positive young adult with intermittent crampy abdominal pain. Over a 10-year period, eight cases of adult intussusception were diagnosed at our institution, and we reviewed the diagnostic computed tomography (CT) scans and records of these patients to correlate them with radiological studies, clinical history, surgical findings, laboratory studies, pathologic analysis, and outcome. Three of the eight patients with adult intussusception had AIDS, all diagnosed by CT scans. Their average age was 41 years, whereas average age of the non-HIV-associated patients was 63. These findings suggest that HIV- and AIDS-associated gastrointestinal pathology provide lead points for intussusception and are significant risk factors for intussusception in young adults. We reviewed the five previously reported cases of AIDS and intussusception and conclude that intussusception should be a diagnostic consideration in an HIV-positive young adult with abdominal complaints. It is clear that AIDS-associated intussusception is a real clinical problem and that CT is an effective method of diagnosing it.

Helical CT of the liver: clinical application of an automated computer technique, SmartPrep, for obtaining images with optimal contrast enhancement.

OBJECTIVES: The purpose of this study was to evaluate an automated computer technique (SmartPrep) for achieving a consistently high level of contrast enhancement in the liver with helical CT. The technique compensates for variability between patients by indicating graphically the time at which scanning should be initiated to reach a desired level of hepatic enhancement. MATERIALS AND METHODS: One hundred nine consecutive patients undergoing helical CT of the abdomen were randomly evaluated, using either a standard 70-sec delay from the start of the injection of contrast material to scanning or a newly developed, commercially available automated technique, SmartPrep. A series of multiple low-dose scans was performed until an arbitrary threshold of hepatic enhancement (50 H) over baseline was achieved. Three regions of interest (ROIs) were imaged on a baseline scan and on contrast-enhanced scans at the upper, mid, and lower liver. Average hepatic enhancement and the standard deviation over baseline was calculated for each group at all anatomic levels. For the SmartPrep group, the range of time between scan initiation and onset of scanning was calculated. RESULTS: The mean hepatic enhancement for the control group (n = 56) was 59.8 +/- 20.1 H, which differed significantly (p = .0002) from that for the SmartPrep group (n = 53), which was 71.6 +/- 15.2 H. Comparison of the variability between the two groups' enhancement levels was also significant (p = .02). The range of delay times for the SmartPrep group was 48-86 sec. In two additional cases, abnormal graphically displayed enhancement curves were the first indication of an improper injection. CONCLUSION: Use of SmartPrep yields a greater and more consistent level of hepatic enhancement from patient to patient than does use of a conventional fixed delay time. The ability to scan more efficiently to achieve greater hepatic enhancement using SmartPrep has significant implications for potential contrast cost savings.

Imaging of the liver: a survey update of prevailing techniques for conventional CT scanning.

BACKGROUND: A survey of the Society of Computed Body Tomography/Magnetic Resonance (SCBT/MR) was performed to assess current techniques in liver CT scanning. METHODS: The study was designed as an update to a study performed in 1987. The survey was distributed to 67 members of the SCBT/MR at 35 institutions. RESULTS: Twenty-six institutions responded. As in 1987, none relied solely on noncontrast scans. In 1987, only 54% (12/22) of institutions performed contrast-enhanced scans as their primary technique compared with 73% (19/26) in 1993. Ionic contrast was used exclusively in the earlier study, whereas in the present study 58% used nonionic contrast in the majority of cases and 38% used nonionic contrast routinely. In 1987, 41% performed scans with a power injector compared with 85% in the present study. Enhanced scans were performed during the contrast bolus in 36% of institutions in 1987 compared with 76% in this study. No institution relied on noncontrast scans alone. In the previous study the delay between injection and scanning was variable (0-60 s), whereas in the present study 83% specified a delay of 21-45 s. CONCLUSION: Significant refinements in CT technique, wider use of power injectors, utilization of nonionic contrast, and a more critical approach to optimize liver imaging have created a significant impact on the practice of liver CT.