Enhanced displays of medical images: evaluation of the effectiveness of color, motion, and contour for detecting and localizing liver lesions

RATIONALE AND OBJECTIVES

Many perceptual studies have shown that the detection of large, low-contrast targets is better either in color or in contrast-reversing presentations than in standard gray scale. We determined the value of several new display techniques for viewing liver computed tomography (CT) scans.

METHODS

Eight observers (four radiologists and four nonradiologists) viewed sets of 100 liver CT images (50 with lesions and 50 without) under five display conditions on a Macintosh computer: (1) color (equiluminant color contrast); (2) color-luminance (combined luminance and chromatic contrast); (3) flicker (luminance contrast that reversed polarity at 2 Hz); (4) contour (shaded intensity mapping); and (5) control (conventional gray scale). Receiver operating characteristics (ROC) techniques were used for analysis.

RESULTS

The measured ROC curve areas for the different viewing conditions were as follows: control = 0.77 +/- 0.01 (mean +/- standard error of the mean); color = 0.78 +/- 0.01; color-luminance = 0.82 +/- 0.01; flicker = 0.78 +/- 0.01; and contour = 0.76 +/- 0.01. The percentage of lesions correctly located ranged from 0.82 (color-luminance) to 0.75 (flicker). Performance under the color-luminance condition was significantly better than in the control condition (p = .01), whereas the other experimental conditions were not significantly different from the control condition (p > .21).

CONCLUSION

The use of mixed color and luminance displays may have perceptual advantages for radiologists and can improve performance over that of gray-scale viewing.

Hepatic MR imaging with ferumoxides: a multicenter clinical trial of the safety and efficacy in the detection of focal hepatic lesions

PURPOSE

To assess the safety and diagnostic efficacy of intravenous ferumoxides, a superparamagnetic iron oxide, for depiction of focal hepatic lesions on magnetic resonance (MR) images.

MATERIALS AND METHODS

This open-label study included 208 patients with known or suspected focal hepatic lesions. MR images were obtained before and 45 minutes to 4 hours after intravenous infusion of ferumoxides (10 mumol/kg). The effect of ferumoxides on signal intensity of the liver was assessed with quantitative analysis. Safety was evaluated with patient monitoring and laboratory measurements.

RESULTS

Mean lesion-to-liver contrast-to-noise ratio on T2-weighted images was 9.1 on unenhanced images and 12.7 on enhanced images. Signal intensity of normal liver on enhanced images decreased to 37% of that on unenhanced images. In blinded image evaluations, additional lesions were identified on 27% of enhanced images. No serious adverse events occurred.

CONCLUSION

Ferumoxides is a safe and efficacious contrast agent for the detection of focal liver lesions on T2-weighted images.

Contrast material-carrying liposomes: biodistribution, clearance, and imaging characteristics

PURPOSE

To assess the biodistribution, clearance, and computed tomographic (CT) imaging characteristics of interdigitation-fusion (IF) liposomes that carry iotrolan in their aqueous phases.

MATERIALS AND METHODS

Biodistribution and clearance of liposomes containing iotrolan produced with the IF method (IF vesicles) were assessed in rats. CT scans of rats and dogs were obtained after injection of IF vesicles at 100 and 250 mg of iodine per kilogram of body weight.

RESULTS

A high initial uptake (63%-96% of the injected dose) was found in the liver and spleen. Liver elimination showed half-lives to be 12.9 days at 250 mg of iodine per kilogram, 10.9 days at 100 mg, and 8.7 days at 25 mg. At 250 mg of iodine per kilogram, the rats had an average of 96 HU of hepatic and 321 HU of splenic enhancement. The dogs had 116 HU of hepatic and 65 HU of splenic enhancement.

CONCLUSION

IF liposomes have favorable biodistribution, clearance, and imaging characteristics as hepatosplenic contrast agents.

Spiral computed tomography of the liver: contrast agent pharmacokinetics and the potential for improved hepatic enhancement

RATIONALE AND OBJECTIVES

We conducted a prospective study of 131 patients to evaluate the contrast agent dose-response relationship for liver spiral computed tomography (CT) and to test the hypothesis that spiral CT scanning provides greater enhancement than does dynamic CT scanning.

METHODS

Patients were assigned to one of two control groups (dynamic CT) or to one of five experimental groups (spiral CT). Dynamic CT patients received 150 ml and spiral CT patients received either 75, 100, or 150 ml of diatrizoate meglumine. All groups had a monophasic injection rate of 2.5 ml/sec. Hepatic enhancement was compared among experimental and control groups.

RESULTS

In the experimental groups, there was a linear dose-response relationship (p < .0001) among the enhancements achieved for the three dosages. The enhancement of the last slice of liver for the spiral CT versus dynamic CT groups receiving 150 ml was significantly greater (p = .002). Peak, first liver slice, and average liver enhancement values were higher with spiral CT scanning, but the difference was not statistically significant (power > .55).

CONCLUSION

Using uniphasic injection rates and identical doses of contrast agent, spiral CT scanning has the advantage of improved enhancement of the last part of the liver to be imaged.

Flattening of the contrast-detail curve for large lesions on liver CT images

This study evaluated the relative roles of physical and perceptual factors in flattening the contrast-detail (CD) curve on liver CT scans. To estimate the role of physical factors, the theoretical CD curve for a calculated theoretical observer (i.e., a nonprewhitening matched filter) was predicted using the measured noise power spectrum and measured modulation transfer function of the CT system. Another theoretical CD curve was also produced from the output of the same calculated observer after taking the human visual response function (VRF) into account. Perceptual factors were evaluated by analyzing human observers' replicated ratings of the visibility of details super-imposed on liver CT scans. The CD curve for the calculated theoretical observer was below the CD curve actually measured for nine human observers and showed no flattening. With the VRF included, flattening of the theoretical CD curves was only produced by fixed image viewing distances of less than 30 cm, a reading style not employed by the human observers. Correlated ROC analysis of observers' replicated ratings indicated that while random, intraobserver variation was present, the magnitude of this so-called observer noise was insufficient to explain the flattening of CD curves. Use of narrow display windows did not eliminate this flattening effect. The main reason for human observers' inefficient detection of large, low contrast liver lesions appears to be a consistent misuse of the image information.

Small (< or = 3 cm) renal masses: correlation of spiral CT features and pathologic findings

OBJECTIVE

We describe our 3-year experience using spiral CT in the evaluation of small renal masses in order to determine the usefulness of this technique for classifying the lesions and to correlate specific CT features with pathologic findings.

MATERIALS AND METHODS

We retrospectively analyzed spiral CT scans and results of pathologic examinations of surgically extirpated small (< or = 3 cm) renal masses in 35 patients. The masses included 27 renal cell carcinomas, two transitional cell carcinomas, one leiomyoma, one angiomyolipoma, and four benign cysts. Several imaging features, including attenuation, pattern of contrast enhancement, presence and type of calcification, cyst wall, and septation, were correlated with pathologic findings.

RESULTS

Most renal cell carcinomas had a solid growth pattern (n = 19), had attenuation values on unenhanced scans of 20 H or greater (n = 26), and had attenuation values that increased by at least 10 H with contrast enhancement (n = 26). Only three renal cell carcinomas were mostly cystic on pathologic examination. Heterogeneous enhancement correlated with the presence of acellular regions (p = .02). Of 12 cystic masses, spiral CT showed the absence of a thick or nodular fibrous capsule in seven of nine masses (specificity, 0.78) and the absence of several (or nodular) septations in six of seven masses (specificity, 0.86) but was not as sensitive in detecting these features.

CONCLUSION

Spiral CT can show many of the key imaging features of small renal masses used to distinguish between benign and malignant lesions. However, despite the theoretical benefits of volumetric CT, some lesions remain indeterminate and require surgical removal for diagnosis.

Design and implementation of a new radiology consultation service in a teaching hospital

The steady increase in costs related to testing has been a major factor in the overall growth of health care expenses. Concern is substantial about the excessive number of tests ordered by physicians without measurable improvement in patients' outcomes. This is of particular concern in teaching hospitals, because in addition to the direct impact on national health care expenditures, these are the institutions in which young physicians train and formulate test-ordering practices. Proper selection of imaging tests is a complex process that requires detailed information about the patient; specific questions to be answered; and knowledge of the characteristics of the test, including sensitivity, specificity, risks, and cost. To date, no systematic method exists for combining the expertise of the radiologist with that of the referring physician before the tests are selected. Therefore, we designed a new clinical service within the radiology department that allows formal, on-the-ward consultation to assist internal medicine housestaff in the selection of radiologic tests. The goal of this study was to assess the feasibility of this formal radiology consultation service and to determine how often its imaging recommendations were implemented for patients with complicated medical conditions.

Spiral CT of the abdomen: region coverage with a 24-second breath-hold

A retrospective review of 75 spiral CT examinations of the abdomen was performed to assess: (1) patient's ability to sustain a 24-s breath-hold, and (2) the proportion of targeted regions or organs that were completely imaged at different table feed speeds. Seventy of 72 patients sustained a 24-s breath-hold without motion artifact. Region coverage depended on the prescribed table feed speed and length of exposure. With a fixed exposure time, there was a tradeoff between the volume of tissue that could be imaged and the slice colimation.

Dual-angled CT-guided biopsy

A new computed tomographic (CT)-guided biopsy technique is described which employs angling both the CT-gantry and the patient to access lesions considered unapproachable using conventional CT techniques. Angling the gantry and the patient, or dual angulation, was applied in five patients with masses located in the pelvis and retroperitoneum that were not easily accessible using gantry angling or patient tilting alone. In each case, the needle tip was demonstrated in the lesion and diagnostic tissue was retrieved. No complications were recorded. A dual-angled approach defines a safe path to a mass and allows obtaining a CT image in the plane of the biopsy needle.

Expediting the turnaround of radiology reports: use of total quality management to facilitate radiologists' report signing

OBJECTIVE

The purpose of this study was to determine whether total quality management techniques could be used to speed radiologists' performance on the task of signing reports.

SUBJECTS AND METHODS

Total quality management represents a group of tools that can be used to improve the functioning of complex processes in the workplace. The steps involved in our total quality management project were as follows: (1) commit to improving radiologists' performance, (2) commission an interdisciplinary study team, (3) propose hypotheses for the causes of signing delays, (4) identify the key issues constraining performance (Pareto analysis), (5) intervene to correct systematic problems in a test system, (6) evaluate the results of intervention on radiologists' report signing performance, and (7) hold the gains achieved by the intervention. An interdisciplinary study team identified five key obstacles to prompt signing of reports: (1) radiologists' absence from the department when reports were available for signing (e.g., nights and weekends), (2) dysfunctional hand-off between transcriptionist and radiologist, (3) requirement that a fellow or resident sign before a staff radiologist, (4) lack of a system for signing by proxy (if primary radiologist is away), (5) perceived lack of impact of signed report on clinical decision making.

RESULTS

Interventions included (1) providing home computer terminals, (2) implementing a buddy system for proxy signing, (3) eliminating the requirement for a signature from a fellow or resident, (4) teaming groups of radiologists with specific transcriptionists, and (5) streamlining transcription service. When these enhancements were used in a test system, the mean time required to sign reports decreased 59% from 26.0 +/- 8.4 hr (mean +/- standard error) in the baseline period to 10.6 +/- 2.9 hr (in the enhanced period, p = .05).

CONCLUSION

We conclude that total quality management methods can accelerate radiologists' signing of reports.

Impact of positive findings at image-guided biopsy of lymphoma on patient care: evaluation of clinical history, needle size, and pathologic findings on biopsy performance

PURPOSE

To analyze the effect of findings at image-guided biopsy of abdominal lymphoma (IGBL) on patient care and define the key determinants of clinical success.

MATERIALS AND METHODS

A retrospective, bi-institutional study was performed in 102 patients with positive or suspicious IGBL findings (93 patients with non-Hodgkin and nine patients with Hodgkin lymphoma). The proportion of patients treated on the basis of IGBL findings only was calculated and correlated with 10 determinants, including history of lymphoma, biopsy technique, needle size, immunocytochemical findings, and tumor grade.

RESULTS

Overall, 73 patients (72%) were treated on the basis of biopsy findings only, including 41 (91%) of 45 patients with a history of lymphoma and 32 (56%) of 57 patients with no such history (P < .01). No difference in findings existed when three needle-size groups were compared (P > .50).

CONCLUSION

Whenever findings were positive, IGBL provided enough tissue to enable treatment in most patients. Fine needles were just as likely as larger needles to enable both determination of tumor grade and treatment.

Three-dimensional imaging and display of renal tumors using spiral CT: a potential aid to partial nephrectomy

OBJECTIVE

A new technique for creating three-dimensional (3D) images of renal tumors using contrast-enhanced spiral computed tomography (CT) is described and preliminarily investigated.

METHODS

3D spiral CT was employed in 2 patients before radical nephrectomy and in 5 patients before partial nephrectomy. Preoperative and postoperative image analyses were conducted to evaluate the ability of the images to depict key anatomic relationships in planning partial nephrectomies.

RESULTS

3D spiral CT defined the tumor's location and relationship to the kidney surface better than the tumor's proximity to renal hilar vessels and collecting system. Negative surgical margins were obtained in all 4 patients with renal cell carcinoma, and post-operative serum creatinine remained less than 2 mg/dL in all 5 patients after partial nephrectomy.

CONCLUSIONS

This early experience suggests that 3D spiral CT can help in the planning of partial nephrectomy and in attaining complete resection of renal cell carcinoma while conserving normal renal tissue.

Prospective comparison of T2-weighted fast spin-echo, with and without fat suppression, and conventional spin-echo pulse sequences in the upper abdomen

PURPOSE

To evaluate use of fast spin-echo (FSE) magnetic resonance imaging with and without fat suppression in the liver and upper abdomen.

MATERIALS AND METHODS

Conventional spin-echo (SE) T2-weighted, FSE T2-weighted, and fat-suppressed FSE T2-weighted images from 37 patients strongly suspected to have focal hepatic lesions were evaluated.

RESULTS

Quantitative analysis demonstrated that fat-suppressed FSE imaging had the highest lesion-liver contrast-to-noise ratio; conventional SE imaging, the lowest. In a qualitative analysis, FSE imaging was preferred. In a rank order analysis, FSE imaging was preferred 83% of the time and fat-suppressed FSE imaging 17% of the time as regards overall image quality; fat-suppressed FSE imaging was preferred 64% of the time, FSE imaging 23% of the time, and conventional SE imaging 13% of the time as regards signal abnormality detection.

CONCLUSION

FSE imaging with and without fat suppression is a potentially useful pulse sequence for evaluating the upper abdomen.

Predictive value of image-guided adrenal biopsy: analysis of results of 101 biopsies

A retrospective study of 97 patients undergoing 101 image-guided adrenal biopsies (IGABs) was performed to analyze the effects of specific pathologic results on test characteristics. Three categories of pathologic results (benign adrenal tissue, malignant tissue, and nondiagnostic) were compared with outcomes. Diagnostic samples were obtained in 86% of cases. Among 72 patients with proved outcomes, IGAB had an accuracy of 96%, a sensitivity of 93%, and a negative predictive value of 91% (92% in patients with bronchogenic carcinoma). In this subset of patients, 33 had biopsy specimens that contained benign adrenal tissue. In these 33 patients, three masses (each smaller than 3 cm) proved malignant. In the 14 patients with nondiagnostic samples, two masses proved malignant. Obtaining benign adrenal tissue was highly predictive of benignity, even in the setting of lung cancer. The authors conclude that IGAB is an accurate procedure in both oncologic and nononcologic patients. However, when the biopsy specimen does not contain benign adrenal tissue or malignant cells, repeat percutaneous biopsy or surgery should be considered.

Combining evidence from multiple imaging modalities: a feature-analysis method

This study was designed to develop methods to improve radiologists' ability to detect and diagnose breast cancer. We evaluated the ability of a feature-analysis method to help radiologists merge judgements constructively from two rather disparate breast imaging tests. To accomplish these goals, we developed a list of perceptual features and quantitated the importance of each in the diagnosis of patients having both diaphanography (Test 1) and mammography (Test 2). Then, two decision aids were developed: One was a checklist of the critical diagnostic visual features from both tests that also assisted readers in rating these features numerically. The second was a computer-based classifier that assisted readers in merging the assessments of the two tests into one overall diagnostic probability. The value of these aids was assessed by comparing radiologists' accuracy in reading a set of proven cases in their standard fashion with their accuracy when reading in an enhanced mode, utilizing the checklist and computer classifier. When Test 1 was read adjunctively with Test 2, use of the decision aids led to a significant improvement in accuracy (p = .013) over the unenhanced, combined readings. For Test 1 alone, the aids led to a significant improvement over its low level of unenhanced reading (p = .046). For Test 2 alone, the enhancements provided little gain in accuracy over an already high level of performance on the full case set (p = .081), although significant gains were realized on the most difficult ones. We conclude that methods to aid standardization and merging of feature-based judgements can improve radiologists performance on complex diagnostic tasks.

Needle-tip localization during CT-guided abdominal biopsy: comparison of conventional and spiral CT

OBJECTIVE

This study was performed to determine whether the time required for needle-tip localization during biopsy of the abdomen would be reduced if continuous-volume data acquisition, also known as spiral CT, were used for guidance instead of conventional CT.

SUBJECTS AND METHODS

Forty patients had biopsies of an abdominal mass; half underwent needle-tip localizations with conventional CT and half with spiral CT. The times required to localize the needle for 104 needle passes were calculated; scanning and reconstruction times were included, and the radiologist's technique and procedural difficulties were deliberately excluded. The mean needle localization times with conventional and spiral CT were compared for the upper abdominal and pelvic regions by using the two-tailed unpaired Student's t-test.

RESULTS

The mean time (+/- SE) for spiral CT was 35 +/- 2 sec compared with 105 +/- 18 sec for conventional CT (p < .001). When analyzed by region, times with spiral CT were shorter in both the upper abdomen (means, 37 sec for spiral CT vs 150 sec for conventional CT, p < .001) and pelvis (means, 25 sec for spiral CT vs 74 sec for conventional CT, p = .038); the magnitude of the improvement was greater in the upper abdomen.

CONCLUSION

The time required to find the needle tip during guided biopsy of an abdominal mass is reduced with spiral CT compared with conventional CT. This improvement is partly a result of the ability to eliminate respiratory misregistration with spiral CT, which is not possible with conventional multisectional CT; hence the greater advantage in upper abdominal biopsy.

Improved radiology film library operations

An interdisciplinary task force at the authors' institution developed a design for a new film library that placed heavy emphasis on service to its customers. The task force established locations and staffing for "satellite" inpatient film libraries organized by clinical specialties. Inpatient films were not permitted to be taken from the radiology department but were available for 24-hour viewing. Film locations were recorded in the radiology information system. Reorganization led to important improvements in film library operations and in the clinical staff's opinion of film library service. Objective measures of performance, such as the fraction of requested films available for conferences, showed significant improvement (P less than .001). Closer working relationships developed between film librarians, radiologists, and their clinical colleagues. Film library personnel were recruited more easily and stayed on the job longer. Several hundred thousand film-tracking transactions per year were recorded. The authors conclude that decentralization of certain film library activities improved many critical aspects of performance.

Contrast-detail curves for liver CT

Contrast-detail curves were constructed for liver computed tomographic (CT) images using an objective method. Stimuli were created by superimposing disks at specified locations on sets of 92 normal liver CT images. Bright and dark disks of 9 sizes and 36 possible image contrasts were used. Sets of 92 stimuli were rendered on film at five window widths (64, 128, 256, 512, and 1024 HU). The contrast-detail (CD) curve flattened substantially for disks larger than 7-mm diameter, and its slope (on a log-log plot) was less than predicted from signal-detection theory. Manipulation of display window manipulation had little impact on this disks' visibility. The results indicate that human observers have difficulty visualizing large, low-contrast details on liver CT scans, and suggest that narrowing the display window will have little effect on this limitation.

Reading and decision aids for improved accuracy and standardization of mammographic diagnosis

Image-reading and decision aids were designed to improve the accuracy of mammogram interpretation. The reading aid was a list of diagnostic radiographic features and scales for quantification of each feature. The decision aid, a computer program, converted the reader's scaled values, weighted for predictive power, into an advisory estimate of the probability of malignancy. The features were identified and their importance was assigned in four steps: (a) interviews of five expert readers to establish an initial set of features, (b) perceptual tests to refine the feature set, (c) a consensus meeting to refine this set and establish nomenclature and scales, and (d) the expert's scaling of each feature in a set of 150 mammograms. Those scaled judgments were analyzed to provide the final list of features and their relative importance and to program the computer decision aid. To test the enhancement effect, six other radiologists interpreted a different set of mammograms without, and later with, the two aids. Receiver operating characteristic analysis showed a gain of approximately 0.05 in sensitivity or specificity when the other value remained at 0.85. In a subset of the more difficult cases, the enhancement effect was approximately 0.15 in either sensitivity or specificity.

Marketing CT and MR imaging services in a large urban teaching hospital

A three-phase marketing program was implemented to increase referrals for examination with computed tomographic (CT) or magnetic resonance (MR) imaging and improve services in an academic radiology department. In the research phase, a data base of 135 referring physicians was developed, and a questionnaire was mailed to 130 physicians. The market research identified three key issues: waiting time to get an appointment, scheduling procedures, and communication of findings. In the implementation phase, additional equipment was installed and a program of expanded appointments, service improvements, and public relations was introduced. In the evaluation phase, 1 year after the completion of phase 2, the effect of the marketing program was measured. The average number of physicians who made referrals per month increased from 609 to 653 (an increase of 7.2% over baseline); the average number of CT and MR examinations performed each month increased by 57.3% and 45.2%, respectively. Referrers' ratings of 10 imaging services improved significantly (P = .02). It is concluded that a well-designed marketing program can boost the productivity of a teaching hospital department.

Practices and attitudes about cathode-ray tube-based and film-based image interpretation

A questionnaire was mailed to 708 practicing radiologists and 348 members of the Society for Computer applications in Radiology (SCAR) in order to evaluate current practices and attitudes regarding the perceived advantages or disadvantages of film- and CRT-based image interpretation. A total of 27% of the 1,056 questionnaires (137 practicing radiologists; 145 SCAR members were returned. Ninety percent of practicing radiologists used film at least 75% of the time. Advantages of film-based reading listed by more than 75% of the respondents included: film reading is faster, and facilitates viewing multiple images. Advantages of CRT-based reading included: access to the entire dynamic range and potential imaging processing. Desirable attributes of existing displays included: adjustable grey scale, magnification, ability to view multiple images, allow quick review, and viewing by several individuals. Valued potential advances included: multiple higher resolution monitors, image processing and multimodality display. Practicing radiologists and computer applications society members had similar attitudes. Film-based reading is still nearly universal, but radiologists are interested in CRT-based reading if such devices have the proper features and become more available.

Current use of screening laboratory tests before abdominal interventions: a survey of 603 radiologists

A survey of 2,153 radiologists was conducted to assess both their current practices of evaluating hemostatic function and their use of blood tests before performing image-guided nonvascular abdominal interventions. Among the 603 (28%) who responded, more radiologists routinely perform prothrombin time (81%) or partial thromboplastin time (78%) tests than platelet counts (59%), and relatively few (7%) obtain bleeding times. The most common practice (51%) is to order all of the first three tests. Use of laboratory tests is quite common (greater than 75%) before biopsy of splenic masses, hemangiomas, or hepatomas and before all catheter insertions. These tests are used less frequently (less than or equal to 70%) before fine-needle procedures, including biopsy and cyst aspiration. Only one-third of the radiologists alter their evaluation in patients who have taken aspirin. Most respondents (64%) believe that there should be written guidelines on how to evaluate patients before interventional procedures. Virtually all (97%) thought such evaluation should be the radiologist's responsibility.