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

Measuring acetabular dysplasia in plain radiographs

BACKGROUND

Several radiologic parameters have been used to qualify an acetabular coverage in studies determining whether an association exists between acetabular dysplasia and osteoarthritis of hip. However, it is not known which parameter is optimum for these epidemiologic studies. We evaluate the reliability, validity, and robustness of the radiologic parameters of acetabular coverage used in these studies.

METHODS

Center-edge angle (CEA), acetabular depth (AD), acetabular angle (AA), acetabular roof obliquity (ARO), and roof angle (RA) were evaluated. The components of intra- and interobserver reliability were tested. The correlations between each parameter were used to depict convergent validity. The robustness of the parameters to different projection (urogram), different definitions of the lateral acetabular margin, and a differing pelvic tilt were evaluated.

RESULTS

The intra- and interobserver reliabilities of CEA, AD and AA ranged from 0.777 to 0.925. The CEA, AD and AA showed acceptable validity in the correlation. The AD on the urograms was 22.0% higher than those on the standing hip radiographs (P < 0.001). When the osteophyte was included in the definition of lateral acetabular margin, the CEA and AD increased significantly (P < 0.001). In simulating pelvic tilting, the AD increased significantly with the anterior pelvic tilt (P < 0.001). The ARO and RA showed poor clinical relevance.

CONCLUSION

When measuring acetabular dysplasia, the AD is unsuitable for use, because it is not robust to different projection of beam and different pelvic tilts. Furthermore, one should consider that the CEA and AA are significantly influenced by different definitions of lateral acetabular margin.

What imaging studies are necessary for abdominal aortic endograft sizing? A prospective blinded study using conventional computed tomography, aortography, and three-dimensional computed tomography

OBJECTIVE

Preoperative imaging modalities for endovascular abdominal aortic aneurysm repair (EVAR) include conventional computed tomography (CT), aortography with a marking catheter, and three-dimensional computed tomography (3D CT). Although each technique has advantages, to date no study has compared in a prospective manner the reproducibility of measurements and impact on graft selection of all three modalities. The objective of this study was to determine the most useful imaging studies in planning EVAR.

METHODS

Twenty patients being considered for EVAR were enrolled prospectively to undergo a conventional CT scan and aortography. The CT scans were then reconstructed into 3D images using Preview Treatment Planning Software (Medical Media Systems, West Lebanon, NH). Four measurements of diameter and six of length were made from each modality in determining the proper graft for EVAR.

RESULTS

Measurements from all three modalities were reproducible with intraobserver correlation coefficients of 0.79 to 1.0 for aortography, 0.87 to 1.0 for CT, and 0.96 to 1.0 for 3D CT. Measurements between observers were also similar from each modality; interobserver correlations were 0.70 to 0.97 for aortography, 0.76 to 0.97 for CT, and 0.73 to 0.99 for 3D CT. Significant differences ( P < .01) in diameter measurements were noted at D2 with aortography compared with 3D CT, whereas differences in length measurements were found between CT and 3D CT at L4 (nonaneurysmal right iliac) ( P < .01). The correlation between CT and 3D CT for most length measurements was acceptable (0.63 to 1.0). Aortography for diameters correlated poorly (0.35 to 0.67) with 3D CT. When the endograft selected by aortography/CT or 3D CT alone was compared with the actual endograft used, there was agreement in 11 of 11 patients when adjusted for +/- one size in diameter or length.

CONCLUSION

Reproducible and comparable measures of diameter and length can be obtained by each of three imaging modalities available for endograft sizing. As a single imaging modality, 3D CT appears to have the best correlation for both diameters and lengths; however, the difference is not sufficient enough to alter endograft selection. Three-dimensional CT may be reserved for challenging aortic anatomy where small differences in measurements would affect patient or graft selection for EVAR.

Angioscanner hélicoïdal de l’aorte abdominale

The purpose was to illustrate that single or multirow spiral CT angiography has become the main modality for the examination of the abdominal aorta. Our multidisciplinary group investigates weekly 15 abdominal aortas, with a single slice spiral CT since 1995, and a 4 row detector spiral CT since 1999. CT scans protocols and parameters optimization for the 2 CT systems are described. Indications and results of CT to investigate the various abdominal aortic diseases are illustrated and discussed: aneurisms (pretherapeutic staging, selection of indications of endovascular stent-grafting); obstructive aorto-arteriopathies (pretherapeutic staging, follow up after endovascular revascularization); dissection (diagnosis, pretherapeutic staging, follow up); inflammatory diseases; normal patterns and principal complications after surgery. Situations where multislice CT is superior to single slice CT and compared advantages of MRI are discussed. CT is at the present time the main technique to image abdominal aorta. Multislice CT is especially interesting to explore the whole aorta, poly traumatisms, and to plan and follow up endovascular treatments.

Quand, comment et pourquoi réaliser une imagerie d’un anévrisme de l’aorte abdominale ?

Usually atherosclerotic in origin, aneurysms of the abdominal aorta (AAA) tend to involve the infrarenal aorta. Their biphasic exponential growth pattern, initially slow then accelerated, results in a risk of rupture. Surgical management is recommended for aneurysm diameters of 45-50mm or for growth rates more than 5mm in 6 Months. Imaging is useful for detection and follow-up of nonsurgical aneurysms, presurgical evaluation of aneurysms, and postsurgical follow-up. Frequently asymptomatic, AAA frequently is an incidental finding at the time of abdominal US. The size of the aneurysm sac, the presence of a neck and the size of the iliac arteries are assessed at the time of initial US detection. US is sufficient for follow-up of small aneurysms. Cross sectional imaging evaluation is necessary when surgery is contemplated. Readily available, multidetector row CT scanners with advanced image post-processing capabilities provide all the necessary information prior to surgical or endovascular management: evaluation of the aneurysm sac and neck, iliac and visceral arteries, and adjacent organs. Angiography with graduated catheters remains sometimes indicated. MR angiography provides results similar to CT but is less readily available and is usually reserved for patients with contraindication to iodinated contrast material. While follow-up imaging after surgical management is seldom performed, it is mandatory after endovascular management and includes KUB, Doppler US and CT or MR angiography.

Helical CT in emergency radiology

Today, a wide range of traumatic and nontraumatic emergency conditions are quickly and accurately diagnosed with helical computed tomography (CT). Many traditional emergency imaging procedures have been replaced with newer helical CT techniques that can be performed in less time and with greater accuracy, less patient discomfort, and decreased cost. The speed of helical technology permits CT examination of seriously ill patients in the emergency department, as well as patients who might not have been taken to CT previously because of the length of the examinations of the past. Also, helical technology permits multiple, sequential CT scans to be quickly obtained in the same patient, a great advance for the multiple-trauma patient. Higher quality CT examinations result from decreased respiratory misregistration, enhanced intravenous contrast material opacification of vascular structures and parenchymal organs, greater flexibility in image reconstruction, and improved multiplanar and three-dimensional reformations. This report summarizes the role and recommended protocols for the helical CT diagnosis of thoracic aortic trauma; aortic dissection; pulmonary embolism; acute conditions of the neck soft tissues; abdominal trauma; urinary tract stones; appendicitis; diverticulitis; abdominal aortic aneurysm; fractures of the face, spine, and extremities; and acute stroke.

Three-dimensional CT angiography of the thorax: clinical applications

Spiral CT with three-dimensional (3D) display can provide a rapid noninvasive examination of the vascular system and has been shown to have a wide range of clinical applications in the thorax, including imaging of the aorta, pulmonary vasculature, and venous abnormalities. Three-dimensional images can provide views of the imaging volume from innumerable viewing angles for both the radiologist and referring clinician, and potentially obviate invasive procedures such as angiography. In this article, we will review many of these applications of spiral CT angiography with 3D displays. Emphasis is placed on study design, protocol selection, and display of pathology.

Three-dimensional CT angiography: renal applications

CT angiography has become an effective noninvasive imaging modality for evaluating the renal vasculature. The current clinical applications for CT angiography and three-dimensional (3D) imaging related to the kidneys and renal vasculature include evaluation of renal artery stenosis, renal diseases related to aortic diseases, living-related renal donor candidates, and preoperative evaluation of renal masses for possible nephron sparing surgeries. Imaging parameters need to be individually prescribed for renal CT angiography depending on the diagnostic goal of the examination. Methods for optimizing spiral CT protocols including patient preparation, contrast administration, image acquisition parameters, and image reconstruction will be covered.

Spiral CT: vascular applications

Recent technical advances in CT have renewed interest in the development of CT angiography (CTA). CT angiography is a minimally invasive method of visualising the vascular system and is becoming an alternative to conventional arteriography in some situations. Spiral technology allows a volume of data to be obtained on a single breath-hold with no respiratory misregistration. Fast machines with second or subsecond acquisition times mean the images are obtained while there are high circulating levels of contrast medium giving peak vascular opacification from a peripheral intravenous injection. Accurate timing will ensure either the arterial or venous phase is imaged. Multiple overlapping axial images can be obtained from the data set with no increase in radiation dose to the patient and from these scans computer generated multiplanar and 3D images are obtained which can be viewed from numerous angles. CT angiography can be performed more quickly, less invasively and at reduced cost compared to conventional angiography.

CT angiography of the visceral vessels

CT angiography (CTA) is a promising new technique for vascular imaging. This review focuses first on the technique necessary for successful scanning of the visceral vessels. As in many new modalities, there are different protocols for scanning and rendering of images. The relative strengths and weaknesses of these different approaches are discussed. A discussion of the applications of CTA to depict normal and abnormal anatomy of the visceral vessels follows. These applications include celiac stenosis, splenic artery aneurysms, evaluation for hepatic arterial anatomy before liver transplantation, visceral arterial anatomy in pancreaticoduodenal surgery, the superior mesenteric artery in intestinal ischemia, vascular encasement in patients with pancreatic neoplasms, and, finally, the hepatic vessels before hepatic tumor resection.