Directed migration of smooth muscle cells to engineer plaque-resistant vein grafts.

PURPOSE: To test the hypothesis that controlled perivascular release of tissue plasminogen activator (tPA) can generate cleaved extracellular matrix (ECM) chemotactic gradients to guide the migration of vascular smooth muscle cells (SMCs) away from the lumen, thereby limiting neointima formation. METHODS: This hypothesis was tested in rabbit models in which the perivascular surface of vein bypass grafts was treated with microspheres releasing tPA (MS-tPA), microspheres containing no drug (MS-blank), or phosphate buffered saline (PBS). Vein graft segments harvested after 7 days were then evaluated for elastin content, proliferating SMCs, intima-to-media (I/M) ratio, and inflammation; late impact on neointima formation was also examined. RESULTS: The 7-day results demonstrated cleaved elastin gradients and proliferating SMCs that assumed a more peripheral distribution in the MS-tPA group than MS-blank and PBS controls (p<0.05). At 28 days, vein grafts treated with MS-tPA showed a mean I/M ratio (0.35+/-0.04) that was 63.5% lower than PBS controls (0.96+/-0.07, p<0.005) and 43.5% lower than MS-blank specimens (0.62+/-0.08, p<0.05). CONCLUSIONS: Perivascular release of tPA modifies ECM gradients, directionally guides SMC migration away from the lumen, and limits neointima formation.

Sensitivity encoding as a means of enhancing the SNR efficiency in steady-state MRI.

Sensitivity encoding (SENSE) with a receiver coil array is typically used as a means of reducing the scan time in MRI. The speed benefit usually comes at some expense in terms of the signal-to-noise ratio (SNR) efficiency, which has been notorious as the main downside of SENSE and parallel MRI in general. In this work it is shown that in steady-state gradient-echo imaging the parallel approach may as well be used to increase the SNR efficiency. The basic idea is to balance reduced phase encoding by increasing the repetition time. In this fashion both the acquisition duty cycle and the steady-state magnetization can be enhanced, resulting in considerable net gains in SNR yield. It is argued that the reduction factor in parallel imaging is essentially an additional degree of freedom in optimizing the SNR. The optimal SENSE factor depends on scan, tissue, and hardware parameters, assuming values up to 3.0 and higher. The achievable SNR benefit also depends on the spoiling regime and is most pronounced for RF-spoiled techniques. The proposed mechanism is demonstrated by simulations and phantom experiments, as well as by contrast-enhanced angiography in vivo, achieving an approximate doubling of the SNR efficiency.

Local resistance to oxidative stress by overexpression of copper-zinc superoxide dismutase limits neointimal formation after angioplasty.

PURPOSE: To examine the effects of oxidative stress on neointimal hyperplasia through local overexpression of human copper-zinc superoxide dismutase (Cu-Zn SOD). METHODS: The left common femoral arteries (CFA) of 18 New Zealand white rabbits were subjected to balloon overdilation injury. Each dilated CFA was then incubated with either a nonviral (buffer) or viral (adenovirus overexpressing beta-galactosidase) control or an adenovirus overexpressing Cu-Zn SOD. Animals were then sacrificed at 3, 7, or 28 days (3 arteries per group per time point) and the treated CFA segments were harvested for analysis of esterase-positive inflammatory cells and extracellular matrix elements. The intima-to-media ratio (I/M) was measured to assess the degree of neointimal formation. RESULTS: At 3 days, local SOD levels in the Cu-Zn SOD-treated group were significantly elevated relative to both controls (p<0.01). Significant reductions in lipid peroxidation byproducts were also seen in the SOD group relative to viral and nonviral controls (p<0.05). Mean I/M at 28 days was 0.582+/-0.088 for the nonviral control group versus 0.565+/-0.133 for the viral control group. The SOD-treated group had a significant reduction relative to both controls: 0.259+/-0.045 (p<0.05). Statistically significant reductions in I/M were also demonstrated in the SOD group relative to control groups at 7 days (p<0.05). The SOD-treated group demonstrated significant preservation of elastin relative to controls, as well as a significant reduction in esterase-positive granulocytes relative to controls (p<0.05). CONCLUSIONS: Direct buffering of oxidative stress in balloon-injured vessels can significantly alter postinjury response and limit neointimal hyperplasia.

Thin-section CT of the lung: does electrocardiographic triggering influence diagnosis?

PURPOSE: To determine the impact of prospective electrocardiographic (ECG) triggering on image quality and diagnostic outcome of thin-section computed tomography (CT) of the lung. MATERIALS AND METHODS: Forty-five consecutive patients referred for thin-section CT of the lung were examined with prospectively ECG-triggered and nontriggered thin-section CT of the lung with a multi-detector row helical CT scanner. Subjective image quality criteria (image noise, motion artifacts, and diagnostic accessibility) were rated by three radiologists in consensus for the upper lobe, middle lobe and/or lingula, and lower lobe. Pathologic changes were assessed for the various lobes, and a diagnosis was assigned. The diagnoses were compared by two radiologists in consensus to determine the effects of CT technique on diagnostic outcome. Quantitative measurements were performed, including determination of image noise and signal-to-noise ratios in different anatomic regions. The Wilcoxon signed rank test and paired sign test (both with Bonferroni correction) were used for statistical analysis. RESULTS: Subjective assessment showed significant differences in motion artifact reduction in the middle lobe, lingula, and left lower lobe. The diagnostic assessibility of triggered CT was rated significantly higher only for the left lower lobe compared with nontriggered data acquisition. No differences in diagnostic outcome were determined between triggered and nontriggered techniques. Mean image noise in tracheal air was 68.2 +/- 17 (SD) for triggered CT versus 37.4 +/- 9 for nontriggered CT (P <.05). Mean signal-to-noise ratio in the upper versus lower lobes was 22.5 +/- 8 versus 25.4 +/- 10 for triggered and 35.6 +/- 9 versus 39.2 +/- 10 for nontriggered techniques (P <.05). CONCLUSION: Given the lack of improvement in diagnostic accuracy and the need for additional resources, ECG-triggered thin-section CT of the lung is not recommended for routine clinical practice.

Aortoiliac and renal arteries: prospective intraindividual comparison of contrast-enhanced three-dimensional MR angiography and multi-detector row CT angiography.

PURPOSE: To compare contrast material-enhanced three-dimensional (3D) magnetic resonance (MR) angiography and multi-detector row computed tomographic (CT) angiography in the same patients for assessment of the aortoiliac and renal arteries, with digital subtraction angiography (DSA) as the standard of reference. MATERIALS AND METHODS: DSA, 3D MR angiography, and multi-detector row CT angiography were performed in 46 consecutive patients. A total of 769 arterial segments were analyzed for arterial stenosis by using a four-point grading system. Aneurysmal changes were noted. The time required for performing 3D reconstructions and image analysis of both MR and CT data sets was measured. Patient acceptance for each modality was assessed with a visual analogue scale. Statistical analysis of data was performed. RESULTS: Sensitivity of MR angiography for detection of hemodynamically significant arterial stenosis was 92% for reader 1 and 93% for reader 2, and specificity was 100% and 99%, respectively. Sensitivity of CT angiography was 91% for reader 1 and 92% for reader 2, and specificity was 99% and 99%, respectively. Differences between the two modalities were not significant. Interobserver and intermodality agreement was excellent (kappa = 0.88-0.90). The time for performance of 3D reconstruction and image analysis of CT data sets was significantly longer than that for MR data sets (P <.001). Patient acceptance was best for CT angiography (P =.016). CONCLUSION: There is no statistically significant difference between 3D MR angiography and multi-detector row CT angiography in the detection of hemodynamically significant arterial stenosis of the aortoiliac and renal arteries.

ECG-gated multi-detector row CT for assessment of mitral valve disease: initial experience.

Our objective was to evaluate applicability and image quality of contrast-enhanced, retrospectively ECG-gated multi-detector row CT (MDCT) for visualization of anatomical details of the mitral valve and its apparatus, and to determine the value of MDCT for diagnosing abnormal findings of the mitral valve. Twenty consecutive patients with mitral valve disease underwent MDCT preoperatively. Two readers assessed visibility of the mitral valve annulus, mitral valve leaflets, tendinous cords, and papillary muscles by using a four-point Likert grading scale. Abnormal mitral valve findings [thickening of the mitral valve leaflets, presence of mitral annulus calcification (MAC), and calcification of the valvular leaflets] were compared with preoperative echocardiography and intraoperative findings. Visibility of the mitral valve annulus and mitral valve leaflets was good or excellent in 15 patients (75%) and in 19 patients (95%) for papillary muscles. The MDCT yielded a 95-100% agreement compared with echocardiography and surgery with regard to the assessment of mitral valve leaflet thickening and the presence of calcifications of the mitral valve annulus or mitral valve leaflets. Intermodality agreement between MDCT and echocardiography was excellent with regard to classification of mitral valve leaflet thickness (kappa=1.00) and good regarding classification of MAC thickness (kappa=0.73). Contrast-enhanced, retrospectively ECG-gated MDCT allows good to excellent visualization of anatomical details of the mitral valve and its apparatus, and demonstrates good agreement with echocardiography and surgery in diagnosing mitral valve abnormalities.

Electrocardiographically gated multi-detector row CT for assessment of valvular morphology and calcification in aortic stenosis.

PURPOSE: To evaluate the applicability and image quality of nonenhanced and contrast material-enhanced multi-detector row computed tomography (CT) combined with retrospective electrocardiographic (ECG) gating for visualization of the aortic valve, determination of aortic valve morphology and diameter of the aortic valve annulus, and assessment of the degree of valvular calcification in patients with aortic valve stenosis, as compared with results of surgery and echocardiography. MATERIALS AND METHODS: Prior to surgical valve replacement, 25 patients with aortic valve stenosis and sinus rhythm underwent nonenhanced (n = 15) and contrast-enhanced (n = 25) retrospectively ECG-gated multi-detector row CT. Two readers working in consensus evaluated image quality and assessed valvular morphology and the degree of valvular calcification. In addition, the diameter of the aortic valve annulus was measured. Results were compared with surgical and echocardiographic findings by using the paired sign test, kappa statistics, and the method of Bland and Altman. RESULTS: The aortic valve could be visualized nearly free of motion artifacts on all multi-detector row CT images. Image quality and diagnostic confidence for classification of aortic valve morphology were significantly superior on contrast-enhanced rather than nonenhanced images (P =.004 and P =.006, respectively). Nonenhanced and contrast-enhanced CT showed good agreement with surgical findings with regard to quantification of the degree of aortic valve calcification (kappa = 0.77 and kappa = 0.74, respectively). Measurement of the diameter of the aortic valve annulus was more reliable on contrast-enhanced images. CONCLUSION: Contrast-enhanced retrospectively ECG-gated multi-detector row CT allows determination of aortic valve morphology, measurement of the diameter of the aortic valve annulus, and assessment of the degree of aortic valve calcification in patients with aortic stenosis.

Multidetector CT: detection of active hemorrhage in patients with blunt abdominal trauma.

OBJECTIVE: The aim of this study was to determine the imaging findings and the prevalence of active hemorrhage on contrast-enhanced multidetector CT in patients with blunt abdominal trauma. MATERIALS AND METHODS: Contrast-enhanced multidetector CT images of 165 patients with blunt abdominal trauma were reviewed for the presence of extravasated contrast agent, a finding that represents active hemorrhage. The site and appearance of the hemorrhage were noted on multidetector CT images. These findings were compared with surgical and angiographic results or with clinical follow-up. RESULTS: On multidetector CT images, active hemorrhage was detected in 22 (13%) of 165 patients with a total of 24 bleeding sites (14 intraperitoneal sites and 10 extraperitoneal sites). Active hemorrhage was visible most frequently as a jet of extravasated contrast agent (10/24 bleeding sites [42%]). Diffuse or focal extravasation was less frequently seen (nine [37%] and five [21%] bleeding sites, respectively). CT attenuation values measured in the aorta (mean, 199 H) were significantly higher than those measured in extravasated contrast material (mean, 155 H) (p < 0.001). Sixteen (73%) of 22 patients with active bleeding on multidetector CT images underwent immediate surgical or angiographic intervention. One patient received angiographic therapy 10 hr after undergoing multidetector CT, and five patients died between 1 and 3 hr after multidetector CT examination. CONCLUSION: Active hemorrhage in patients after blunt abdominal trauma is most frequently visible as a jet of extravasated contrast agent on multidetector CT. When extravasation is detected, immediate surgical or angiographic therapy is required.

Experience of 4 years with open MR defecography: pictorial review of anorectal anatomy and disease.

Functional disorders of the pelvic floor are a common clinical problem. Diagnosis and treatment of these disorders, which frequently manifest with nonspecific symptoms such as constipation or incontinence, remain difficult. Fluoroscopic x-ray defecography has been shown to aid in detection of functional and morphologic abnormalities of the anorectal region. With the advent of open-configuration magnetic resonance (MR) imaging systems, MR defecography with the patient in a vertical position became possible. MR defecography permits analysis of the anorectal angle, the opening of the anal canal, the function of the puborectal muscle, and the descent of the pelvic floor during defecation. Good demonstration of the rectal wall permits visualization of intussusceptions and rectoceles. Excellent demonstration of the perirectal soft tissues allows assessment of spastic pelvic floor syndrome and descending perineum syndrome and visualization of enteroceles. MR defecography with an open-configuration magnet allows accurate assessment of anorectal morphology and function in relation to surrounding structures without exposing the patient to harmful ionizing radiation.

Traumatic injuries: imaging of abdominal and pelvic injuries.

The availability of new imaging modalities has altered the diagnostic approach to patients with abdominal and pelvic trauma. Computed tomography and ultrasound have largely replaced diagnostic peritoneal lavage. Ultrasound is used in most trauma centers as the initial imaging technique for the detection of hemoperitoneum and helps to determine the need for emergency laparotomy. Computed tomography allows for an accurate diagnosis of a wide range of traumatic abdominal and pelvic conditions. The speed of single-detector helical and multi-detector row CT (MDCT) permits a rapid CT examination of the seriously ill patient in the emergency room. In particular, the technology of MDCT permits multiple, sequential CT scans to be quickly obtained in the same patient, which is a great advance in the rapid assessment of the multiple-injured patient. The evolving concepts in trauma care promoting non-operative management of liver and splenic injuries creates the need for follow-up cross-sectional imaging studies in these patients. Computed tomography and, less frequently, MR or ultrasound, are used for this purpose.

Dynamic MR imaging of the pelvic floor performed with patient sitting in an open-magnet unit versus with patient supine in a closed-magnet unit.

PURPOSE: To compare open-magnet magnetic resonance (MR) imaging performed with the patient sitting with dynamic closed-magnet MR imaging of the pelvic floor performed with the patient supine. MATERIALS AND METHODS: Thirty-eight patients underwent dynamic 1.5-T closed-magnet pelvic floor MR imaging while in the supine position. Midsagittal T2-weighted single-shot fast spin-echo and T1-weighted multiphase spoiled gradient-recalled-echo (SPGR) MR images were obtained before and after rectal contrast agent administration, respectively, with the patient at rest, straining, and maximally contracting the sphincter. Subsequently, the patient was transferred to an open 0.5-T system. Midsagittal multiphase T1-weighted SPGR MR images were then obtained every 2 seconds with the patient sitting while at rest, maximally contracting the sphincter, straining, and defecating. Images were analyzed with regard to presence of enteroceles, anterior rectoceles, intussusceptions, rectal descents, bladder descents, and vaginal vault descents. RESULTS: All intussusceptions were missed at supine MR imaging. With sitting MR imaging as the reference standard, the sensitivity of supine MR imaging was 79% for depiction of bladder descents. When MR findings were graded and clinically irrelevant MR findings were excluded, sensitivity increased to 100% for depiction of bladder descents and anterior rectoceles and to 96% for depiction of rectal descents. CONCLUSION: Dynamic supine MR imaging performed with a closed-configuration unit before and after rectal contrast agent administration appears to be an alternative to sitting MR defecography performed with an open-configuration unit for diagnosis of clinically relevant pelvic floor abnormalities.

Multidetector-row helical CT: analysis of time management and workflow.

The purpose of this study was to evaluate time management and workflow for multidetector-row helical CT (MDCT). Time for patient and data handling of at total of 580 patients were evaluated at two different time periods (December 1999, August 2000), each for the following baseline measurements: (a) change of clothes/instruction; (b) patient placement on the CT table/i.v. catheter; (c) CT planning and programming; (d) CT data acquisition; (e) CT data reconstruction; (f) CT data storage/printing. All imaging was performed on a Somatom Volume Zoom (Siemens, Erlangen, Germany). Time measurements summarized for different CT protocols revealed the following: (a) 5:01 min (+/- 2.06 min); (b) 4:36 min (+/- 2.43 min); (c) 4:11 min (+/- 2.55 min); (d) 0:43 min (+/- 0.15 min); (e) 6:59 min (+/- 2.39 min); (f) 09:51 min (+/- 3.51 min). Planning and programming was most time-consuming for CT angiography, whereas chest and abdominal CT needed only 3:26 and 3:30 min, respectively. Reconstruction time was highest for HRCT (9:22 min) and CTA (9:03 min). Data storage/printing was most time-consuming for HRCT (13:02 min), followed by combined neck-chest-abdomen examinations (12:19 min). Comparing the two time periods, during which a software update was performed, a mean time reduction of 4:31 min per patient (15%, p<0.001) was achieved. Whereas CT data acquisition time is no longer a problem with MDCT, patient management, data reconstruction, and data storage are the most time-consuming parts. Well-trained technicians, state-of-the-art workstations, and fast networking are the most important factors to improve workflow.

Thoracic aorta: motion artifact reduction with retrospective and prospective electrocardiography-assisted multi-detector row CT.

The authors compared prospective (n = 20) and retrospective (n = 20) electrocardiography (ECG)-assisted multi-detector row computed tomography (CT) with non-ECG-assisted multi-detector row CT (n = 20) of the thoracic aorta with regard to reduction of motion-related artifacts. Image quality was rated for transverse source and sagittal oblique images of the thoracic aorta, including the aortic valve. ECG-assisted multi-detector row CT compared with non-ECG-assisted multi-detector row CT showed a significant reduction in motion artifacts for the entire thoracic aorta.

Secondary aortoenteric fistula: active bleeding detected with multi-detector-row CT.

We report a case of active bleeding of a secondary aortoenteric fistula (SAEF), in which CT angiography with multi-detector-row CT (MDCT) was finally diagnostic after negative catheter angiography and unsatisfactory endoscopy. The MDCT angiography clearly demonstrated the fistulous tract between the abdominal aortic graft and the duodenum. The dynamic process of bleeding was confirmed as a net increase of contrast agent accumulation in the duodenum through different phases. The MDCT angiography with its excellent 3D image quality is therefore a valuable method in the assessment of active SAEF bleeding.