Conspicuity of hepatic metastases on helical CT: effect of different time delays between contrast administration and scanning

OBJECTIVE

The purpose of this study was to compare two time delays between injection of contrast material and helical CT scanning to determine relative conspicuity of hepatic metastases.

SUBJECTS AND METHODS

Twenty-five patients with hepatic metastases were examined with helical CT. The first imaging phase was initiated at 50 sec and the second 75 sec after the start of contrast material injection (3 ml/sec, 150 ml). Differences in lesion and liver attenuation were measured quantitatively. Four radiologists used a 5-point scale to assess lesion conspicuity subjectively.

RESULTS

Mean differences in enhancement between liver and lesion were 41 H during the first phase and 59 H for the second phase (p = .0001). Radiologists' conspicuity score averaged 2.4 for lesions in the first phase versus 3.3 for lesions in the second phase (p = .0001). In 56 (88%) of 64 lesions, objective measurements showed greater enhancement of lesions during the later phase. Radiologists found 60 (94%) of 64 lesions to be more conspicuous on these later images.

CONCLUSION

Our results show that conspicuity of hepatic metastases on helical CT scans is better with a 75-sec scan delay between contrast administration and scanning than with a 50-sec scan delay. The longer delay time should be used when scanning is used to detect metastases.

Helical CT: practical considerations and potential pitfalls

Helical (spiral) computed tomography (CT) is having a dramatic impact on body imaging. Unlike conventional CT, helical CT provides continued volumetric acquisition as the patient moves through the gantry. Advantages of helical CT include dramatically shortened examination times, improved visibility of vascular structures, better enhancement of parenchymal organs, the capability for retrospective imaging and three-dimensional (3D) vascular studies, and potential reduction in use of contrast material. However, helical CT requires one to be more cognizant of the relationship between contrast material administration and scanning, since the optimal temporal window for detection of disease can be missed. Factors unique to helical technology can produce artifacts, which one must be aware of when interpreting helically generated scans. Many of these artifacts relate to accentuation of vascular or parenchymal enhancement. Others occur during production of high-quality 3D images. Additional artifacts are sure to be identified with increased experience with helical CT.

The optimal temporal window for CT of the liver using a time-density analysis: implications for helical (spiral) CT

OBJECTIVE

Scanning protocols for conventional CT of the liver have been proposed. Current availability of helical CT with a four- to sixfold decrease in scan time requires significant adjustments in these protocols. The present study assesses the implications of time-density curves on the performance of helical liver CT.

MATERIALS AND METHODS

Twenty patients without liver lesions were studied for time-density analysis of the aorta, inferior vena cava (ICV), portal vein, and liver. Scans were performed at the level of the portal vein at baseline and every 15 s for 3 min following uniphasic administration of 150 ml (300 mg I/ml) nonionic contrast agent. Regions of interest were used to measure three areas in each anatomic structure over time. Median and mean peak enhancement times were calculated for all 20 patients. Cubic spline interpretation was employed to determine the point of equilibrium.

RESULTS

Results demonstrated the following average maximum enhancement values and times for peak enhancement: aorta: 227 HU (75 s); liver: 123 HU (105 s); portal vein: 187 HU (90 s); IVC: 142 HU (90 s). Hepatic enhancement achieved 67 HU over baseline. Peak portal enhancement occurred 15 s prior to liver enhancement (p = 0.001). Aortic and hepatic curves became parallel (onset of equilibrium) at a median time of 120 s.

CONCLUSION

Helical scanning requires a longer delay (70-80 s) than used for conventional CT. Upon application of these principles, scan initiation occurs higher on the liver enhancement curve, improving liver enhancement without impinging on equilibrium.

Abdominal aortic aneurysms: evaluation with variable-collimation helical CT and overlapping reconstruction

PURPOSE

To determine the value of variable collimation and overlapping reconstruction in helical computed tomography (CT) to evaluate abdominal aortic aneurysm.

MATERIALS AND METHODS

Twenty-three patients (15 men and eight women, aged 59-85 years) underwent helical CT scanning, nine with fixed 5-mm collimation and 14 with 3- and 7-mm collimation combined. The ability to visualize main and accessory renal arteries, detect stenoses, and determine aneurysm extent were evaluated.

RESULTS

Extent of aneurysm was accurately determined in 17 of 23 cases without overlapping sections; failure to detect ancillary findings such as accessory arteries or stenosis occurred in nine of these cases. With overlapping sections, determination of aneurysm extent improved to 19 of 23 cases and ancillary errors were reduced to four. Five errors occurred with fixed collimation and three errors with variable collimation.

CONCLUSION

Overlapping, variable-collimation helical CT allows for a more complete evaluation of abdominal aortic aneurysms than does nonoverlapping, fixed-collimation CT.

Preoperative assessment of abdominal aortic aneurysm: the value of helical and three-dimensional computed tomography

PURPOSE

The purpose of this study was to evaluate the utility of helical computed tomography (CT) in the preoperative assessment of abdominal aortic aneurysms (AAA) and to compare its accuracy with aortography and operative findings.

METHODS

Thirty-two patients with suspected AAA were evaluated by helical CT with either 5 mm collimation (slice thickness) or a combination of 3 mm collimation through the renal and mesenteric arteries and 7 mm collimation through the remainder of the AAA. Three-dimensional reconstructions were performed with use of three different techniques, and results were compared with aortography and surgery.

RESULTS

Twenty-five patients were found to have an aneurysm, and 19 subsequently underwent surgery. Standard angiography was also performed in 13. The location, size, and extent of the aneurysm, as well as the wall calcification and intraaneurysmal thrombus, were well depicted with helical CT. The visceral aortic branches, including the detection of renal artery stenosis and accessory renal arteries, were consistently seen with the 3 mm/7 mm collimation protocol and three-dimensional reconstruction.

CONCLUSION

Helical CT with three-dimensional display of the aorta and its branches combines the advantages of conventional CT imaging and aortography. This technique appears to provide comprehensive preoperative evaluation of AAA.

Acute diseases of the gallbladder and biliary ducts

Approximately 10% to 15% of adults have gallstones, resulting in more than 600,000 cholecystectomies being performed annually in the United States. It is not surprising, therefore, that biliary disease is a major consideration in the patient with acute abdominal pain. Although there is no substitute for skillful physical diagnosis, the radiologist is often the central player in the evaluation of biliary disease. This article focuses on three specific areas of importance to the radiologist: (1) the diagnostic approach to acute biliary disease, (2) imaging of specific clinical entities, and (3) the relationship between imaging findings and the use of new therapeutic modalities.

Three-dimensional models of the abdominal vasculature based on helical CT: usefulness in patients with pancreatic neoplasms

Three-dimensional (3D) rendering of helical (spiral) CT data is used increasingly to show abnormalities of the vascular system [1]. Abdominal applications have focused mainly on the arterial system, but the portal venous system also can be depicted effectively with this technique. In patients with pancreaticobiliary neoplasms, axial display of helical CT images generally allows accurate staging of the lesion [2, 3]. Many surgeons, however, continue to request arteriography to specifically look for evidence of vascular encasement that would preclude surgery or vascular anomalies that would alter the surgical approach [4, 5]. The purpose of this essay is to illustrate the value of 3D rendering of CT data in providing useful information for surgical planning and showing the extent of vascular involvement by tumor.

Cluster scanning in body CT

Rapid, dynamic computed tomography (CT) is essential in scanning the body in order to maintain adequate contrast enhancement during the entire examination. In the case of the liver, this is most critical in order to complete scanning prior to the equilibrium phase when lesions are less conspicuous or may be missed entirely. This technical note describes the application of "cluster scanning" to conventional scanning in order to optimize body CT by decreasing the total exam time.

Adenomyosis: prospective comparison of MR imaging and transvaginal sonography

PURPOSE

To prospectively compare conventional spin-echo magnetic resonance (MR) imaging and transvaginal sonography for the diagnosis of adenomyosis.

MATERIALS AND METHODS

Twenty women with clinically suspected adenomyosis underwent MR imaging and transvaginal sonography performed within 3 months of each other. Pathologic proof was obtained in all cases.

RESULTS

Seventeen patients were proved to have adenomyosis. The correct diagnosis was achieved with MR imaging in 15 of 17 cases. One false-positive and two false-negative diagnoses were made with MR imaging. With transvaginal sonography, nine of 17 cases of adenomyosis were correctly diagnosed. One false-positive and eight false-negative diagnoses occurred. The most frequent cause of false-negative diagnoses with transvaginal sonography was the misinterpretation of adenomyosis as leiomyomas (seven cases).

CONCLUSION

MR imaging is significantly better (P < .02) than transvaginal sonography in the diagnosis of adenomyosis.

Quantitative ultrasonic detection of parenchymal structural change in diffuse renal disease

OBJECTIVE

The authors determined whether quantitative ultrasound could be useful in the evaluation of diffuse renal disease.

METHODS

Digitized radiofrequency ultrasound data were acquired from the kidneys of patients with biopsy-proven diffuse renal disease and transplant rejection (37 patients plus 18 normal volunteers). The results of the quantitative analysis were compared with histology results to determine if microscopic renal structure could be correlated with quantitative features such as scatterer size and scatterer spacing. The results also were analyzed using receiver operating characteristic analysis to determine if diffuse disease could be detected reliably using quantitative methods.

RESULTS

The three most useful features in the native kidneys were mean scatterer spacing (MSS), sigma's, and average scatterer size (D). Using these features, it was possible to detect diffuse renal disease causing a decrease in renal function with an area under the ROC curve (Az) of 0.93. The feature D corresponded closely to histologically measured average glomerular diameters. For normals, D = 216 microns and glomerular diameter = 211 microns. No histologic correlate was found for scatterer spacing. In transplants, MSS and integrated backscatter were most useful for detecting rejection (Az = 0.87), and D in rejection was similar to the values for normal kidney and normally functioning transplants.

CONCLUSIONS

The D value corresponds to glomerular diameter, and glomerular enlargement can be detected readily using quantitative ultrasound. Combinations of two to four quantitative features can detect diffuse renal disease and transplant rejection reliably.

Laparoscopic cholecystectomy. Postoperative sonographic findings

Seventeen consecutive patients undergoing elective laparoscopic cholecystectomy (LC) were serially evaluated with transabdominal ultrasound before, one day after, and six days after LC to document what, if any, changes occur in the surgical bed and surrounding parenchyma. The most common postoperative finding was focal sonolucency in the hepatic parenchyma adjacent to the gallbladder fossa in six (35%) of 17 patients. Five patients (29%) had postoperative fluid collections in the gallbladder fossa; in four of these five, it was technically difficult to dissect the gallbladder from the liver at the time of original surgery. In one patient the fluid resolved by the sixth postoperative day. It persisted in the remaining four. Two patients had transient ductal dilation and one had pneumobilia. Shadowing and ring-down artifact was identified in 12 patients due to surgical clips in the triangle of Calot. Because gallbladder fossa fluid may persist up to six days after uncomplicated laparoscopic cholecystectomy, caution should be used before attaching significance to isolated imaging findings. Clinical judgement remains the best means of selecting which patients need additional evaluation.

Routine helical CT of the abdomen: image quality considerations

PURPOSE

Both helical and nonhelical abdominal computed tomographic (CT) scans were obtained to compare image quality, study the effect of patient size and collimation, and compare the frequency of visualization of normal abdominal structures.

MATERIALS AND METHODS

The study group consisted of 60 consecutive patients with clinically suspected metastatic malignancy.

RESULTS

Both helical and nonhelical image quality was excellent, with equal mean image quality scores of 4.1 on a 5-point scale. In patients weighing more than 175 lb (79 kg), both helical and nonhelical image quality degraded equally when 5-mm collimation was used; 10-mm collimation resulted in excellent image quality, regardless of patient size. Small in-plane structures (eg, renal arteries, renal veins, pancreatic duct) were seen best on helical scans. With the addition of retrospectively reconstructed overlapping images, improvement in visualization of these structures was statistically significant.

CONCLUSION

Helical CT scanning should be the preferred means of acquiring routine abdominal CT images.

Delayed contrast enhancement of ascitic fluid on CT: frequency and significance

OBJECTIVE

Enhancing peritoneal fluid has been described as an uncommon finding resulting from active extravasation of contrast material from the bowel, urinary tract, or blood vessels. We have noted that enhancing peritoneal fluid occurs in other clinical settings. The CT number of ascites frequently increases between initial images obtained during bolus injection of IV contrast material and delayed images obtained after completion of the routine study. The objective of this study was to define the frequency and clinical significance of this phenomenon.

SUBJECTS AND METHODS

Fifty patients (32 with malignant disease and 18 with benign disease) with free intraperitoneal fluid were examined with abdominal CT with IV contrast material. Active intraperitoneal bleeding or perforation of the bowel or bladder was not clinically suspected in any patient studied. When intraperitoneal fluid was detected on review of initial dynamic scans, a limited number of delayed scans were obtained also. Significant enhancement was determined by comparing the CT numbers of fluid on dynamic and delayed images.

RESULTS

Significant delayed enhancement of intraperitoneal fluid was seen in 54% of patients, with increases averaging 25 H (range, 7-54 H). Parametric analysis indicated enhancement was inversely proportional to the amount of intraperitoneal fluid but independent of the type of IV contrast material (ionic vs nonionic), time delay (range, 10-104 min), clinical history, and serum creatinine and serum albumin levels. Enhancement occurred in both malignant and benign diseases and was more likely when small amounts of ascites were present.

CONCLUSION

Enhancement of intraperitoneal fluid is a common and often striking finding on delayed CT scans after administration of IV contrast material. The phenomenon is nonspecific, occurring in a wide spectrum of clinical conditions. Caution should be used in interpreting the significance of high-attenuation intraperitoneal fluid on delayed images to avoid an erroneous diagnosis of active intraperitoneal bleeding or contrast extravasation.

Improving the distinction between benign and malignant breast lesions: the value of sonographic texture analysis

To improve the ability of ultrasound to distinguish benign from malignant breast lesions, we used quantitative analysis of ultrasound image texture. Eight cancers, 22 cysts, 28 fibroadenomata, and 22 fibrocystic nodules were studied. The true nature of each lesion was determined by aspiration (for some cysts) or by open biopsy. Analysis of image texture was performed on digitized video output from the ultrasound scanner using fractal analysis and statistical texture analysis methods. The most useful features were those derived from co-occurrence matrices of the images. Using two features together (contrast of a co-occurrence matrix taken in an oblique direction, and correlation of a co-occurrence matrix taken in the horizontal direction), it was possible to exclude 78% of fibroadenomata, 73% of cysts, and 91% of fibrocystic nodules while maintaining 100% sensitivity for cancer. These findings suggest that ultrasonic image texture analysis is a simple way to markedly reduce the number of benign lesion biopsies without missing additional cancers.

Laparoscopic cholecystectomy: intraoperative ultrasound of the extrahepatic biliary tree and the natural history of postoperative transabdominal ultrasound findings

Laparoscopic cholecystectomy (LC) has been rapidly embraced as an alternative to conventional open cholecystectomy (OC). While LC is less invasive than OC, it is still a surgical procedure with potential complications such as retained bile duct stones, iatrogenic injury to the bile duct with or without bile leak, hemorrhage, intestinal injury, and abscess formation. This article discusses the feasibility of intraoperative transmural ultrasound of the extrahepatic biliary tree with a 6.2 French catheter-based ultrasound probe and reviews the natural history of postoperative changes in the liver and gallbladder bed with conventional transabdominal ultrasound.

Helical (spiral) CT of the abdomen

Since its clinical introduction in the mid 1970s, techniques for CT have undergone many changes that have dramatically altered how CT scans are obtained. Helical (spiral) CT allows for faster acquisition of truly volumetric CT data than is possible with conventional scanners. Routine helical CT of the abdomen is now possible because of three major technical refinements: the development of the slip-ring gantry, improved detector efficiency, and greater tube cooling capability. This article reviews the technical principles that govern helical CT, the potential advantages and disadvantages of this technique, and initial clinical experience with helical CT of the abdomen.

The effects of a soft tissue mimicking medium and increased power settings on the location and magnitude of lithotripter peak positive pressure

In vitro experiments showed that a tissue mimicking medium alters the peak positive pressure (p+), focal zone properties and frequency content of shockwaves compared with their behavior in water. The reduction in (p+) ranged from 5% at 10 kV. to 19% at 18.1 kV., when measured at the geometric focus with the tissue mimicking medium present. As power settings were increased, the relative gain in pressure was damped by attenuation. A 2 mm. shift in the acoustic focus was seen both axially and laterally with the tissue mimicking medium. While the former is probably not significant, the latter may be clinically significant given the narrow lateral beam width at the acoustic focus. These attenuation experiments suggest that clinical targeting through tissue may not be as precise or result in as high peak pressures as the clinician expects. Especially at high power settings, the depth of tissue traversed should be minimized to limit attenuation effects.

Intraoperative bile duct sonography during laparoscopic cholecystectomy: experience with a 12.5-MHz catheter-based US probe

During elective laparoscopic cholecystectomy, 20 patients underwent intraoperative evaluation of the biliary tract with a commercial 6.2-F, 12.5-MHz catheter-based ultrasound (US) probe. The study tested the feasibility of this technology for mapping the anatomy of the hepatoduodenal ligament and Calot triangle, assessing bile duct integrity, and detecting choledocholithiasis. The duct was studied with a transmural approach, the catheter being placed parallel to, but remaining outside, the bile duct. The common hepatic duct and common bile duct in the vicinity of the cystic duct were seen in all 20 patients; the junction of the cystic duct with the common hepatic duct was seen in nine patients (45%). After the cystic duct was clamped, no sonographic evidence to suggest bile duct injury was noted in any patient. The transmural imaging approach was tested in four pigs in whose common bile duct a single human calculus had been placed. In all instances the size and location of the calculus were accurately detected. Intraoperative US with a catheter-based system is a safe and effective means for interrogation of the extrahepatic biliary tree during laparoscopic cholecystectomy.

Lateral arcuate ligaments of the diaphragm: anatomic variations at abdominal CT

The authors have occasionally observed nodular areas abutting the lateral diaphragmatic surface and extending into the posterior pararenal space on computed tomographic (CT) scans. Review of the anatomy literature revealed that this finding represents inferolateral extension of the lateral arcuate ligaments, which reflect over the quadratus lumborum muscles to fuse with the diaphragm. CT scans from 100 consecutive patients were reviewed to determine the frequency, relationship to habitus, and appearance of this finding. Nodularity was found in five patients (bilateral in three, unilateral in two). The average size was 9.4 mm in the transverse plane, 6.3 mm in the anteroposterior plane, and 4.3 cm in the cephalocaudal plane. The extent of retroperitoneal fat was normal in all five patients. In one patient, there were easily visible lobulations; three patients had prominent lobulations, and one patient had few lobulations. It is important to recognize this anatomic variant to avoid confusion with disease.

Hepatic cavitation. A marker of transient hepatocellular injury during biliary lithotripsy

Sonographically visible microbubbles attributable to cavitation effects have been observed in bile (within the gallbladder), in hepatic vessels, and within the liver of patients undergoing biliary lithotripsy. Cavitation effects are believed to contribute to stone fragmentation and possibly tissue injury during lithotripsy. To study the latter, the relationship between intraparenchymal hepatic cavitation and serum transaminase activity and clinical follow-up was analyzed in 81 patients undergoing 164 lithotripsy treatments. Seventy-one treatments (43%) resulted in sonographically evident microbubbles in the liver parenchyma during lithotripsy. A temporary, yet statistically significant (P < 0.01) rise in SGOT and SGPT was observed within 2 hr of completion of lithotripsy compared to those patients without hepatic microbubbles. All but one patient had a return to pretreatment baseline levels of SGOT and SGPT by two weeks after lithotripsy. In this patient, persistent elevation of transaminases was attributed to the delayed passage of fragments and not to any sequelae from hepatic cavitation effects. Ultrasound immediately after, two weeks after, and 3-12 months after lithotripsy showed no hepatic structural abnormalities. Ursodiol administration at the time of treatment did not predispose to hepatic cavitation or elevation of transaminase. Detection of hepatic microbubbles during lithotripsy is a marker of hepatocellular injury. Their correlation with transaminase elevation refutes the contention that transaminasemia results solely from fragment passage after lithotripsy. Although not associated with recognizable structural damage or long-term sequelae, cavitation effects and transaminasemia reiterate that shockwaves are not entirely benign as they traverse parenchymal organs.

Parameters for predicting electromagnetic lithotripter failure: quality assurance implications

Despite the extensive use of lithotripsy for treating renal and biliary calculi, there has been little data reported regarding the causes and manifestations of lithotripter failure. The clinical and service records for 145 consecutive treatments performed with the Siemens Lithostar Plus were reviewed. Service record analysis revealed eight failures of shock wave generation during a 10-month period. Six of these failures were subtle and still allowed shock wave generation. There were five in-line ultrasound probe failures during this period. The most useful clinical parameter for predicting lithotripter failure was reduced severity of sonographically evident cavitation bubbles during treatment. Lack of stone fragmentation and unexpectedly low analgesia requirements at high-power levels were less useful in predicting lithotripter failure. All clinical parameters suffered from nonspecificity. Preliminary experience, with an ongoing quality assurance program using a test object hydrophone, suggests this is a useful method of predicting lithotripter function and avoiding compromised treatments.

PACS clinical experience at Georgetown University

Georgetown University Hospital has been operating an image management and communications system (IMACS or PACS) for 3.5 years. This work was initially funded under the Army Medical Research and Development Command Digital Imaging Network Systems (DINS) project. The system was taken from a research system supporting only radiology tasks to one extended to clinical use, and has been used in clinical work for 3 years. This paper will summarize our PACS clinical experience and will describe the operational features implemented and those still necessary.