Cumulative radiation dose during hospitalization for aneurysmal subarachnoid hemorrhage

BACKGROUND AND PURPOSE

Radiation exposure from neurointerventional procedures and diagnostic neuroimaging can be substantial, with many recommendations offered to guide the interventionalist in the conscientious use of ionizing radiation. Patients presenting with an aneurysmal subarachnoid hemorrhage can undergo multiple imaging procedures during a prolonged hospital course. Therefore, we reviewed a cohort of such patients to identify the sources and quantify the cumulative radiation exposure seen during their hospitalization.

MATERIALS AND METHODS

We retrospectively reviewed a single-center experience with these patients to define the potential for short-term skin injury and long-term oncologic risk due to absorbed radiation dose and sources of ionizing radiation and their contribution to the cumulative absorbed dose to the cranial tissues.

RESULTS

We demonstrated that substantial cumulative doses can be seen, with 87% of the cumulative absorbed dose occurring during neurointerventional procedures and 7% from CT. Mathematic modeling was performed identifying potential techniques to further reduce the cumulative radiation absorbed dose to these patients.

CONCLUSIONS

We conclude that repetitive irradiation during the care of patients with aneurysmal subarachnoid hemorrhage can result in significant cumulative doses and a variety of techniques can be applied to reduce this absorbed dose. Use of radiation for diagnostic and therapeutic purposes during prolonged procedures of patients with subarachnoid hemorrhage demands diligence throughout the hospitalization.

Spiral CT scanning technique in the detection of aspiration of LEGO foreign bodies

BACKGROUND

Radiolucent foreign bodies (FBs) such as plastic objects and toys remain difficult to identify on conventional radiographs of the neck and chest. Children may present with a variety of respiratory complaints, which may or may not be due to a FB.

OBJECTIVE

To determine whether radiolucent FBs such as plastic LEGOs and peanuts can be seen in the tracheobronchial tree or esophagus using low-dose spiral CT, and, if visible, to determine the optimal CT imaging technique.

MATERIALS AND METHODS

Multiple spiral sequences were performed while varying the CT parameters and the presence and location of FBs in either the trachea or the esophagus first on a neck phantom and then a cadaver. Sequences were rated by three radiologists blinded to the presence of a FB using a single scoring system.

RESULTS

The LEGO was well visualized in the trachea by all three readers (both lung and soft-tissue windowing: combined sensitivity 89 %, combined specificity 89 %) and to a lesser extent in the esophagus (combined sensitivity 31 %, combined specificity 100 %). The peanut was not well visualized (combined sensitivity < 35 %). The optimal technique for visualizing the LEGO was 120 kV, 90 mA, 3-mm collimation, 0.75 s/revolution, and 2.0 pitch. This allowed for coverage of the cadaver tracheobronchial tree (approximately 11 cm) in about 18 s. Although statistical power was low for detecting significant differences, all three readers noted higher average confidence ratings with lung windowing among 18 LEGO-in-trachea scans.

CONCLUSION

Rapid, low-dose spiral CT may be used to visualize LEGO FBs in the airway or esophagus. Peanuts were not well visualized.

Three-dimensional computed tomographic volume rendering techniques in endoscopic thoracoplasty

BACKGROUND CONTEXT

Thoracoplasty is occasionally necessary to achieve an acceptable cosmetic result in the presence of a rib hump, especially in previously fused young adults with scoliosis. This usually requires the resection of four to five rib segments, and the morbidity associated with open posterior resection or of open anterior resection by means of thoracotomy is often considerable, apart from leaving an unsightly scar. We thought the use of an endoscopic internal rib resection technique would achieve the desired result with less morbidity. Our experience with using the technique of three-dimensional (3-D) computed tomographic (CT) volume rendering to plan our portals and releases for endoscopic scoliosis correction led us to believe the same techniques could be adapted to plan and endoscopically carry out the thoracoplasty.

PURPOSE

To define the utility of 3-D CT volume rendering of the spine and thorax in the preoperative planning of endoscopic rib resection.

STUDY DESIGN

A prospective evaluation of the utility of 3-D CT volume rendering for preoperative planning in patients with scoliosis undergoing endoscopic thoracoplasty for correction of rib humps.

PATIENT SAMPLE

Four consecutive patients with previously fused scoliotic spines and pronounced right-sided rib humps requiring operative correction were selected.

OUTCOME MEASURES

Outcome was assessed at a minimum follow-up of 6 months by clinical examination, patient satisfaction with the clinical result, and repeat helical CT scanning with 3-D reconstruction.

METHODS

Four patients with previously fused scoliotic spines and pronounced rib humps underwent helical CT scanning with 3-D volume rendering, prior to endoscopic corrective surgery. All four patients had right-sided rib humps requiring corrective rib resection for cosmetic reasons. Using the technique of 3-D volume rendering, a vector plane was created to mirror the left scapula, and its intersections on the right chest wall were noted. The ribs to be resected were marked, and the length of rib resection was measured from the vector plane's intersection points with the ribs. In this way an estimate of the resection required to achieve the desired final position of the right elevated scapula could be determined. Entry portals were also estimated with vector lines to achieve optimal access to each rib. During surgery, the portal sites were assessed for access to the selected ribs. Also, the extent of rib resections was compared with the estimates. The final clinical outcome was assessed by clinical examination, patient satisfaction with the cosmetic result, and repeat helical CT scanning with 3-D reconstruction.

RESULTS

The male to female ratio was 1:3, and the average age was 21 years. Our average estimated blood loss was 307 ml and average hospital stay was 4.75 days. The estimated portal sites were accurate and did provide for direct access to each selected rib involved in the deformity. We were able to resect the ribs at the points suggested by 3-D CT volume rendering, with the lengths of our resected segments matching our preoperative estimates. In all cases the elevated right scapula did descend into the rib resection bed, thus balancing the shoulder heights. An excellent cosmetic result was achieved in all cases as evaluated by clinical examination, patient's perception, and repeat helical CT scanning.

CONCLUSION

The technique of 3-D CT volume rendering with vector plane estimates provides a reliable estimate of the rib resection required to achieve a cosmetically acceptable correction of the rib hump through minimally invasive techniques.

Preoperative use of 3D volume rendering to demonstrate renal tumors and renal anatomy

With increased use of computed tomography (CT) and abdominal ultrasonography, the indications for nephron-sparing surgery are also increasing. Triphasic helical CT and three-dimensional (3D) volume rendering can be combined into a single noninvasive test to delineate renal tumors and normal and complex renal anatomy prior to nephron-sparing surgery. This combination technique has proved accurate and very useful for both preoperative and intraoperative planning by demonstrating renal position, tumor location and depth of tumor extension into the kidney, relationship of the tumor to the collecting system, and renal vascular anatomy. Knowledge of the position of the kidney relative to the lower rib cage, iliac crest, and spine helps in planning the initial surgical incision. By depicting tumor location and depth of extension, helical CT with 3D volume rendering helps ensure complete tumor excision and conservation of adjacent normal renal parenchyma. Depiction of the relationship of the tumor to the collecting system helps anticipate further tumor extension and minimize postoperative complications. Identification of normal renal vasculature and anatomic variants can help minimize ischemic injury and intraoperative bleeding. Radiologists should be familiar with current indications for nephron-sparing surgery and understand what information is required prior to surgery.

Quantitative analysis of breast parenchymal density: correlation with women's age

RATIONALE AND OBJECTIVES

The authors evaluated the relationship between a woman's breast parenchymal density and her age by means of a quantitative method for measuring density from digitized mammograms.

MATERIALS AND METHODS

The percentage of the breast considered to be dense was evaluated from mammograms of 50 women stratified by age. Quantitative analysis based on the computer segmentation of tissue in digitized mammograms was performed by three expert mammographers. The results of this analysis were compared with results from a review of the film mammograms by three expert mammographers.

RESULTS

A slight decrease in the percentage of breast considered to be dense with increased age was observed. The average difference in the percentage of dense breast tissue between the youngest and the oldest age groups was 6.4% based on the digital review and 14.6% based on the film review. Within each age group, the total variability was on the order of 75%.

CONCLUSION

The difference in mean magnitude between the youngest and oldest age groups was small and may not be clinically important. The variability within an age group was large, which suggests that age is not a reliable indicator of percentage of dense breast tissue.

3-dimensional volume rendered computerized tomography for preoperative evaluation and intraoperative treatment of patients undergoing nephron sparing surgery

Background:

Live donor nephrectomy has gained popularity on account of the laparoscopic technique, to overcome a small donor pool. Laparoscopic donor nephrectomy requires a precise study of the vascular and morphological renal anatomy, as laparoscopy is technically challenging due to the limited field of vision. In-depth knowledge of the renal anatomy before a laparoscopic procedure is essential for a successful transplant. The left kidney is preferred over the right even in cases of multiple vessels because of the long renal vein, which requires precise preoperative vascular mapping. Helical computerized tomography (CT) angiography, with its axial, coronal, and 3D reconstruction, gives a better understanding of renal anatomy. There are instances where the helical CT findings are misleading and less informative in a small number of cases. This study highlights a case study of the helical CT findings compared with the intraoperative findings of 200 live donors, who underwent laparoscopic donor nephrectomy, and the renal anatomy has been understood at the same time.

Aims:

1. To compare the helical CT findings on the operated side with the intraoperative findings. 2. To analyze the CT findings

Materials and Methods:

Two hundred cases of laparoscopic transperitoneal donor nephrectomy were included in this study.

Statistical Method Used:

Chi square test was the statistical test used to compare the findings between CT and the intraoperative data.

Results:

The axial, coronal, and 3D images of the CT findings were on par with the intraoperative findings in most of the cases. Incidental findings help in the better planning of surgery. Multiple vessels on the left side are preferred over the right sided normal anatomy; with not much technical difficulty with the aid of a helical CT. Male donors had more incidences of multiple vessels, gonadal vein, Retroaortic Renal Vein (RARV), lumbar vein, and duplication of ureter, compared to females. Furthermore, these variations are more in the left side donors. Ninety-two percent of the cases in this study are left-sided donors. The helical CT finding shows that renal vein variations are more on the right side.

Conclusions:

Helical CT is important in delineating the arterial, venous, and ureteral anatomy and can show the important incidental findings. Left renal donors and males have more variations in their renal anatomy. Technically challenging laparoscopic nephrectomy on the multiple-vessel-side donor is possible with the aid of helical CT. The importance of the CT in evaluating donor renal anatomy for a technically challenging laparoscopic donor nephrectomy is commendable.

3-dimensional volume rendered computerized tomography for preoperative evaluation and intraoperative treatment of patients undergoing nephron sparing surgery

PURPOSE

Computerized tomography (CT) is the diagnostic and staging modality of choice for renal neoplasms. Existing imaging modalities are limited by a 2-dimensional (D) format. Recent advances in computer technology now allow the production of high quality 3-D images from helical CT. Nephron sparing surgery requires a detailed understanding of renal anatomy. Preoperative evaluation must delineate the relationship of the tumor to adjacent normal structures and demonstrate the vascular supply to the tumor for the surgeon to conserve as much normal parenchyma as possible. We propose that helical CT combined with 3-D volume rendering provides all of the information required for preoperative evaluation and intraoperative management of nephron sparing surgery cases. We prospectively evaluated the role of 3-D volume rendering CT in 60 patients undergoing nephron sparing surgery for renal cell carcinoma at the Cleveland Clinic Foundation.

MATERIALS AND METHODS

Triphasic spiral CT was performed preoperatively in 60 consecutive patients undergoing nephron sparing surgery for renal neoplasms. A 3 to 5-minute videotape was prepared using volume rendering software which demonstrated the position of the kidney, location and depth of extension of the tumor(s), renal artery(ies) and vein(s), and relationship of the tumor to the collecting system. These videotapes were viewed by a radiologist and urologist in the operating room at surgery, and immediately correlated with surgical findings. Corresponding renal arteriograms of 19 patients were retrospectively compared to 3-D volume rendering CT and operative findings.

RESULTS

A total of 97 renal masses were identified in 60 cases evaluated with 3-D volume rendering CT before nephron sparing surgery. There were no complications related to the 3-D protocol and 3-D rendering was successful in all patients. The number and location of lesions identified by 3-D volume rendering CT were accurate in all cases, while enhancement and diagnostic characteristics were consistent with pathological findings in 95 of 97 tumors (98%). Of 77 renal arteries identified at surgery 74 were detected by 3-D volume rendering CT (96%). Helical CT missed 3 small accessory arteries, including 1 in a cross fused ectopic kidney. All major venous branches and anomalies were identified, including 3 circumaortic left renal veins. Of 69 renal veins identified at surgery 64 were detected by 3-D volume rendering CT (93%). All 5 renal veins missed by CT were small, short, duplicated right branches of the main renal vein. Renal fusion and malrotation anomalies were correctly identified in all 4 patients.

CONCLUSIONS

The 3-D volume rendering CT accurately depicts the renal parenchymal and vascular anatomy in a format familiar to most surgeons. The data integrate essential information from angiography, venography, excretory urography and conventional 2-D CT into a single imaging modality, and can obviate the need for more invasive imaging. Additionally, the use of videotape in an intraoperative setting provides concise, accurate and immediate 3-D information to the surgeon, and it has become the preferred means of data display for these procedures at our center.

Selenium-based digital radiography versus conventional film-screen radiography of the hands and feet: a subjective comparison

OBJECTIVE

The purpose of this study was to subjectively compare the visibility of normal anatomy of the hands and feet using selenium-based digital radiography versus conventional film-screen (100-speed) radiography.

SUBJECTS AND METHODS

Digital and film-screen images of the hands and feet of 24 patients were obtained without an antiscatter grid using identical X-ray exposure. Each pair of images was evaluated independently by five experienced radiologists for visibility of normal anatomy using a six-point rating scale. Soft tissues, cortical bone, and trabeculae were evaluated. For each observer, "equivalence" was defined as a mean difference in image quality of less than 1 unit on the 0-5 scale used in the study. Paired t tests were also performed to determine whether the average visibility rating of one technique was statistically superior to that of the other at a .05 level of significance for each observer and at each anatomic landmark.

RESULTS

In all categories, selenium-based digital images were rated equivalent to film-screen images by the five observers. Using the sum of the nine landmarks, four of the five observers rated the quality of selenium-based digital images superior to that of film-screen images.

CONCLUSION

Subjective visibility of normal anatomy of the hands and feet using selenium-based digital radiography was similar to that achieved using conventional film-screen radiography.

Comparison of examination times between CT scanners: are the newer scanners faster?

OBJECTIVE

The purpose of this study was to determine if a newer technology helical CT scanner can reduce CT examination times.

MATERIALS AND METHODS

Data from 1049 CT examinations were recorded prospectively during a 5-week period. "Room time" was defined as the time each patient spent in the CT room (time patient exited minus time patient entered) and "scanner time" was defined as the time a scanner was dedicated to a specific patient (longer of either time that image processing was complete minus time patient entered room, or total time that patient spent in the scanner room). Data to calculate the room and scanner times were recorded along with the scanner type, examination protocol, and five other covariates. Both times were calculated for the 10 most common examination protocols (n = 769 patients) and compared between the older and newer model CT scanner using analysis of covariance models. The most common protocols were abdomen and pelvis (n = 211); head (n = 146); chest (n = 99); simple sinus (n = 99); and chest, abdomen, and pelvis (n = 68).

RESULTS

The mean room and scanner times, adjusted for covariates, were both significantly shorter for the newer scanner (p = .0001). The results for room time were statistically significant for six of the 10 examination protocols (84% of examinations). Likewise, the results for scanner time were statistically significant for four examination protocols (68% of examinations). Examination times were longer for inpatients (p = .0001) and when problems occurred during the examination (p = .0001). Sex and age did not significantly affect examination times (p > .08).

CONCLUSION

The newer helical CT scanner we studied significantly reduced the time for many types of examinations.

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.

Optimization of Cd1-xZnxTe Detectors for Digital Radiography

In this study, measurements of the electrical and detection parameters of the Cd1-xZnxTe detectors, within the x-ray diagnostic energy range, have been performed with the aim of optimizing the image quality parameters of these solid-state-ionization detectors. Namely, the leakage current and system capacitance of the x-ray imaging system have been measured as they relate to signal parameters. Similarly, the detected signal and noise contributions were measured and related to the radiation exposure and tube current setting. Furthermore, the detector contrast has been experimentally determined. The experimental results indicate that Cd1-xZnxTe detectors have low leakage current, high resistivity, and high detector contrast resolution. Therefore, they appear to be very attractive for imaging applications with applications in x-ray digital radiography.

Contrast Study of CdZnTe Detectors for Digital Mammography

Experiments have been performed with the aim of optimizing the image quality parameters of CdZnTe detectors for digital mammography. A geometrical breast phantom has been designed, and the dependence of the contrast resolution of a planar CdZnTe detector on the phantom thickness has been experimentally determined. Specifically, the detected signal and noise contributions were measured and related to phantom thickness. The results of this study indicate that the CdZnTe detectors exhibit a high contrast resolution. On the other hand, the dynamic range of this detector can be improved significantly by further implementation of the data acquisition electronics.

Power injection of intravenous contrast material through central venous catheters for CT: in vitro evaluation

PURPOSE

To determine the feasibility of use of a power injector to deliver contrast material through central venous catheters for computed tomographic (CT) examinations.

MATERIALS AND METHODS

Ioversol 240 and iothalamate meglumine 43% were separately injected through three 9.6-F Hickman catheters and three 10.0-F Leonard catheters with a power injector in an in vitro study. Flow rates of 1.0, 1.5, 2.0, and 2.5 mL/sec were tested. Peak pressures were mechanically recorded from two sites. A 95% prediction interval was calculated for each peak pressure, and the upper limits at the prediction interval were evaluated to determine if it was less than the recommended limit of 25 psi (175 kPa).

RESULTS

Contrast medium, flow rate, and catheter type each statistically significantly affected the measured peak pressures (P = .0001). For each flow rate tested, the upper limits of the prediction interval for the peak pressure at the connection between the coiled tubing and the catheter were below the manufacturer's specified peak pressure.

CONCLUSION

In vitro analysis demonstrates that power injection of intravenous contrast medium through central venous catheters does not exceed the pressure limits of these catheters at the flow rates tested. In vivo testing to evaluate the safety and efficacy of power injection through central venous catheters is necessary.

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.

Determination of spiral CT slice sensitivity profiles using a point response phantom

OBJECTIVE

This study was done to compare the slice sensitivity profiles (SSP) for combinations of collimation, pitch, and table speed for spiral CT using a point response phantom. The goal was to determine the optimal combination of parameters to reduce partial volume averaging without compromising z-axis coverage.

MATERIALS AND METHODS

A copper ball bearing measuring 0.4 mm was embedded in a closed-cell air-foam background to create a point response input phantom. The phantom was scanned at pitches from 0.1 to 2.0 for collimations of 5, 8, and 10 mm. The full width half maximums (FWHMs) and full width tenth maximums (FWTMs) were estimated from SSP curves generated by plotting the maximum pixel value in HU for each reconstructed image against table position. FWHMs and FWTMs were compared separately for constant collimation and increasing table speed and for constant table speed and decreasing collimation using either a two-tailed z-test or chi-square test.

RESULTS

Differences between FWHMs and between FWTMs for comparisons made between different collimations at constant table speeds of 8 and 10 mm/s were significantly different (p < or = 0.0001). Differences between FWHMs and between FWTMs showed a linear trend, increasing with increasing pitch for constant collimation (p < or = 0.0013).

CONCLUSION

Scanning at narrower collimation but higher pitch provides a narrower SSP when scanning at equivalent table speeds without compromising z-axis coverage.

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.

Diagnosis of aortic dissection: value of helical CT with multiplanar reformation and three-dimensional rendering

OBJECTIVE

Twenty-three patients with suspected aortic dissection were evaluated in this preliminary study of helical CT to determine the usefulness of axial sections, multiplanar reformation, and three-dimensional (3D) rendering in assessing the presence of dissection and the extent of intimal flap.

MATERIALS AND METHODS

Patients were referred for helical CT scanning because of chest pain or an abnormal chest radiograph. Scans were performed during bolus injection of nonionic contrast material at 2.0-2.5 ml/sec using a mean scan delay of 47 sec. Axial scans with 5-mm collimation were obtained in all patients. They extended from the great vessels to the distal thoracic aorta just above the hiatus. Delayed nonhelical sections were obtained through the upper abdomen. Multiplanar reformations and 3D models were reconstructed from the helical data in 13 patients and were compared to axial sections in 7 patients who proved to have documented dissection. The efficacy of CT was determined using surgery, angiography, or clinical outcome to establish the diagnosis.

RESULTS

Of the 23 patients studied, axial sections resulted in 15 true-negative, 7 true-positive, and 1 false-positive interpretation. In three of seven patients with dissection, it was difficult to determine the extent of the intimal flap on axial sections; multiplanar reformation or 3D views clarified the relevant anatomy in all 3 cases. Among the 3D display methods, ray-sum projection views were superior to surface model or maximum-intensity-projection views.

CONCLUSION

If studies of larger numbers of patients confirm our preliminary findings, multiplanar reformation and 3D rendering of helical CT scans will be a valuable addition to axial display of CT studies used to detect aortic dissection and to determine the extent of the intimal flap.

Abdominal aortic aneurysms: findings on three-dimensional display of helical CT data

Excellent vascular opacification, reduction in misregistration artifacts, and the option of reconstructing overlapping scans from which three-dimensional (3D) models of the abdominal vessels may be rendered are among the benefits of helical CT [1-4]. The purpose of this essay is to illustrate the findings of 3D rendering of helical CT data in patients with abdominal aortic aneurysms.

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.

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.

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.

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.

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.

Gallstone lithotripsy: results when number of stones is excluded as a criterion for treatment

The Siemens Lithostar Plus protocol (Siemens Medical Systems, Iselin, NJ) allows investigators to perform gallstone lithotripsy on patients regardless of the number of stones they have, provided the stones occupy less than 50% of the gallbladder lumen. The purpose of this study was to determine the interrelationships between stone burden, fragmentation response, and stone-free rates when treatment is not limited to three stones or fewer. Of 200 patients initially examined, 80 (40%) underwent lithotripsy. The mean number of treatments per patient was 2.1, and the mean number of shock waves per patient was 7386. In 60 patients in whom 6-month follow-up was available, the overall stone-free rate, based on actual results, was 32% (19/60). The stone-free rates for solitary stones, two or three stones, and four or more stones were 50%, 12%, and 26%, respectively. Regardless of number of stones, patients who ultimately became stone free had significantly smaller mean fragment size (0.25 cm) 2 weeks after lithotripsy than did those who did not become stone free (0.51 cm). Retrospective volume analysis showed that seven (47%) of 15 patients with multiple stones occupying less than 2000 mm3 were stone free; none became stone free when this volume was exceeded. Lithotripsy remains a practical option for patients with solitary stones. Comparable stone-free rates to those achieved for solitary stones can be obtained in patients with multiple stones, regardless of their number, provided treatment is aggressive and the stone aggregate is less than 2000 mm3.

Gallstone fragmentation during biliary lithotripsy: effect of stone composition and structure

In vitro lithotripsy with the Siemens Lithostar was conducted on 36 radiolucent or minimally calcified gallstones housed in an anthropomorphic phantom. The ease and pattern of fragmentation were correlated with global composition for the entire stone, regional or microcomposition (determined by Fourier-transform infrared spectroscopy), and microstructure (determined by scanning electron microscopy). Stones made up of more than 62% cholesterol required 50% more shock waves to pulverize all fragments to 0.3 cm or less than did stones of less than 62% cholesterol (p less than .01). An inverse relationship was found between the number of shock waves needed for fragmentation and the cholesterol content (r = .77). Although a broad range of fragmentation responses occurred, little variation was seen in the ease of fragmentation within stone families. The majority of stones fractured along radially oriented cholesterol plates, but one third of stones treated showed initial chipping or flaking at the periphery before radial fracture. This type of peripheral erosion most often occurred in stones with peripheral pigment rims. These stones required more shock waves and lagged in pulverization compared with more homogeneous cholesterol stones. The efficiency of fragmentation during biliary lithotripsy correlates with the stones' global cholesterol content. A stone's architecture, as reflected by its regional composition and microstructure, partially predicts the mechanism of fragmentation. These in vitro data may be useful in further refining criteria for selecting patients and understanding the fragmentation process.

Gallstone lithotripsy: relevant physical principles and technical issues

A basic understanding of shock wave generation is essential for the radiologist who performs gallstone lithotripsy. Shock waves differ from ordinary acoustic waves in that they have a rapid rise time, a positive pressure component that gives rise to compressive forces approaching 1,000 atm, and a low-amplitude sustained negative pressure (rarefactive) component. Shock waves are created by means of three different types of shock wave generators: spark-gap, electromagnetic, and piezoelectric. The authors describe and compare these three types of shock wave generators with regard to equipment selection. Regardless of how shock waves are generated, they share common interactions with tissue. These interactions are reviewed along with the proposed mechanisms of stone fragmentation.

Cavitation effects during lithotripsy. Part I. Results of in vitro experiments

Cavitation effects and microbubble formation are due to the rarefactive (negative pressure) component of shock waves. The in vitro application of shock waves generated by a commercial lithotriptor to an anthropomorphic phantom showed that stone fragmentation occurred more completely in fluid media that support cavitation than in a solid agar-graphite gel. Various fluids (saline, iodinated contrast material, bile) supported different degrees of cavitation. Bile exhibited cavitation at low energy and gave rise to intense microbubble formation at 19 kV. Cavitation increased dramatically with an increase in the rate of generation from 1.0 to 1.8 shock waves per second. The authors conclude that during biliary lithotripsy the environment of a stone will influence the extent of cavitation and fragmentation.

Cavitation effects during lithotripsy. Part II. Clinical observations

Cavitation effects during biliary lithotripsy can produce sonographically visible microbubbles. The relationship between microbubble formation and clinical outcome of gallstone lithotripsy performed with a commercial lithotriptor was studied in 50 treatments in 29 patients. Microbubble formation in bile was a useful predictor of successful stone fragmentation in 31 of 34 treatments. Microbubble formation in the liver correlated with transient hepatocellular damage (as indicated by a twofold rise in serum transaminase levels) immediately after seven of 10 treatments. Advancing the focal volume of the lithotroptor deeper into the patient (placing the stone at the proximal point of the focal zone) may be a useful strategy for reducing hepatic cavitation effects, which appear to be responsible for temporary hepatocellular damage.

Relationship between stone motion, targeting, and fragmentation during experimental biliary lithotripsy

In vitro experiments in an anthropomorphic phantom were performed to clarify the relationship between stone motion, targeting, and fragmentation. Stone motion was minimized by pinning the stone against the dependent wall of a mock gallbladder cavity during shock wave treatment. Fragmentation was most effective (probably due to increased cavitation effects) when the shock wave traversed fluid at the point of its impact with a stone. The results suggest that treatment with the patient in the supine or oblique position may produce a better outcome than treatment in the prone position. Buoyant stones exhibited the greatest motion, which was often to-and-fro in nature. Although restricting the size of the mock gallbladder cavity reduced stone motion, maintaining a 1-cm fluid path was beneficial for achieving optimal pulverization.

Visibility of gallstone fragments at US and fluoroscopy: implications for monitoring gallstone lithotripsy

To assess the value of ultrasound (US), fluoroscopy, and spot radiography in the detection, counting, and measurement of gallstone fragments during lithotripsy, in vitro visibility studies were conducted on fragments from 20 stones. Fluoroscopic visibility was evaluated during and after lithotripsy on 185 fragments placed in an anthropomorphic phantom. Three US experiments were performed on the fragments to study the visibility of fragments as a function of size, the accuracy of the count with large numbers of fragments, and the ability of observers to detect and count fragments larger than both 4 mm and 5 mm. With fluoroscopy, fragment detection rates ranged from 20% (fragments larger than 2.5 mm) to 80% (fragments larger than 4.5 mm). With US, all fragments larger than 1.5 mm were detected, and US was significantly better than fluoroscopy and spot radiography for detection of fragments 2.5 mm or smaller. US was also more accurate than fluoroscopy (11% vs 59% error) in the assessment of the number of fragments. When fragments larger than 4 mm or 5 mm were being counted with US, 92% of the fragments were visualized. The results suggest that US is more accurate for monitoring gallstone lithotripsy than fluoroscopy or spot radiography.

Renal calculi after shock wave lithotripsy: US evaluation with an in vitro phantom

Fragments of renal calculi from patients who had undergone extracorporeal shock wave lithotripsy (ESWL) were embedded in an in vitro tissue-equivalent ultrasound (US) phantom to assess (a) the accuracy with which such fragments could be measured; (b) the influence of stone composition, stone depth, and transducer frequency; and (c) the effect of fragment "clumping" on size determinations and acoustic shadowing. Fragments as small as 0.8 mm in diameter could be detected at 7.5 MHz, although a practical limitation of 1-2 mm for lower transducer frequencies (3.5 and 5.0 MHz) was observed. Fragment diameter tended to be overestimated with US by a mean of 1 mm. Transducers of 5 and 7.5 MHz were more accurate in determination of size than 3.5-MHz transducers. Struvite fragments were less echogenic and were therefore measured more accurately, but smaller struvite fragments were less detectable than other fragment types. Fragment "clumping" led to significant overestimation of residual stone size even when small fragments were separated by as much as the distance equal to the diameter of one fragment. This study demonstrates that even under the best circumstances the disadvantages of US in assessing residual stone disease are significant.

Breast mass detection by US: a phantom study

Phantoms were used to compare imaging of various masses in the glandular region for two types of breasts. In one type, normal glandular tissue contains no fat clumps; in the other type, randomly distributed spherical fat clumps exist. The size distribution and number of fat clumps per unit volume in the phantoms represented those found in actual normal glandular tissue. For a 5-cm path length between the scanning window of the phantom and the centers of the masses, the presence of the fat clumps caused distortions and deviations of the beam, resulting in image distortion. This degradation was reduced when successive slabs of the material containing the fat clumps were removed. Image degradation appeared to be less severe when a 2.25 (rather than a 3.5) MHz transducer was used. The results show that the thickness of tissue containing fat clumps between the scanning transducer and a mass plays a role in the detectability of masses and diagnostic usefulness of the image of a breast. This suggests that imaging of the breast in the compressed configuration should be performed regardless of whether the freely suspended breast is imaged. Also, transducers of lower nominal frequency may have an important role in breast imaging.