Evaluation of Peripheral Arterial Bypass Grafts with Multi–Detector Row CT Angiography: Comparison with Duplex US and Digital Subtraction Angiography

Intermodality agreement between TTE and low kVp ECG-gated MDCTA in diagnosis of complex CHD in pediatrics

Background

Transthoracic echocardiography (TTE) is considered the primary diagnostic modality in congenital heart disease (CHD). However, it has limited role in evaluation of extra-cardiac major vessels abnormalities. Cardiac catheterization angiography is considered the gold standard investigation, yet, it is invasive. The aim of this study is to evaluate the agreement between TTE and low kVp ECG-gated cardiac multi-detector CT angiography (MDCTA) in detecting cardiac and extra-cardiac findings of complex congenital heart disease in a sample size of 36 patients (19 males and 17 females) with an age ranged between 30 days and 12 years (mean age 25.5 months). All cases were diagnosed to have complex CHD clinically and by TTE then referred to undergo cardiac low kVp ECG-gated MDCTA to confirm diagnosis and for better assessment of extra-cardiac major vessels abnormalities. Data derived from both modalities were then compared to calculate the inter-technique variability by using Cohen’s kappa statistics.

Results

TTE diagnosed 96% of intra-cardiac anomalies and only 54% of extra-cardiac major vessels anomalies detected by MDCTA, with variable degrees of intermodality agreement in detection different anomalies ranging between perfect agreement in diagnosing most of intra-cardiac lesions and very poor agreement in diagnosing extra-cardiac SVC anomalies.

Conclusion

Low kVp ECG-gated cardiac MDCTA is a rapid, non-invasive and reliable diagnostic modality in complex congenital heart diseases. It confirms TTE findings in intra-cardiac anomalies and significantly surpasses TTE reliability in diagnosis of extra-cardiac major vessels anomalies. So, it is indispensable as part of adequate preoperative assessment algorithm in cases of complex CHD and can't be replaced by TTE even with the later providing accurate assessment of intra-cardiac anomalies.

A simple, refined approach to diagnosing renovascular hypertension in children: A 10-year study

BACKGROUND

Despite advances in non-invasive vascular imaging, detection of renal artery stenosis via catheter angiography is the criterion standard for the diagnosis of renovascular hypertension (RVH). However, because of lack of evidence, the utility of various blood tests and imaging modalities remains unclear.

METHODS

We retrospectively analyzed the utility of blood tests (plasma renin activity [PRA], aldosterone, and renal vein renin [RVR] values) and imaging studies (computed tomography angiography [CTA], kidney ultrasonography [US]) by comparing them with catheter angiography. Ten pediatric patients with RVH at two institutions from January 2008 to December 2017 were recruited. The sensitivities for diagnosing RVH via imaging and blood tests (kidney [US], PRA, and aldosterone) were derived by examining patient records. Furthermore, the sensitivity and specificity of CT angiography were calculated by considering both the affected and non-affected renal arteries of the patients.

RESULTS

A high sensitivity for diagnosing RVH via kidney US (89%) and PRA (80%) was observed. The sensitivity and specificity of CTA were 100%, each. RVR sampling did not aid in the diagnosis of RVH; only two of six patients with unilateral RVH showed significant laterality of RVR boundary ratios. Renal scintigraphy facilitated detection of a non-functional kidney (split renal function <5%).

CONCLUSIONS

RVH in children could be diagnosed utilizing non-invasive blood and imaging tests, without catheter angiography. We recommend kidney length measurement along with measurement of PRA level, as a simple and highly useful screening test, followed by CTA as a diagnostic test.

Radiation dose and image quality with new protocol in lower extremity computed tomography angiography

PURPOSE

To compare radiation dose and image quality of lower extremity computed tomography angiography (CTA) between cranio-caudal acquisition with single-source CT (SSCT) and flash caudo-cranial acquisition with dual-source CT (DSCT).

MATERIALS AND METHODS

In this prospective study, 60 patients were randomly assigned to Group A (control) or Group B (experimental) to undergo lower extremity CTA for peripheral obliterative arterial disease. Group A received protocol 1 (P1) with SSCT cranio-caudal acquisition. Group B received protocol (P2) with DSCT flash caudo-cranial acquisition. Intravascular attenuation (IVA), signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR) and image noise were compared. Two radiologists assessed the image quality. Computed tomography volume dose index (CTDI_vol) and dose-length product (DLP) were also compared.

RESULTS

IVA with P2 was higher than with P1 (586.8 ± 140.3 vs. 496.1 ± 129.3 HU, p = 0.011), as was SNR (33.0 ± 11.3 vs. 27.4 ± 12.3; p = 0.042), CNR (30.1 ± 13.3 vs. 24.2 ± 10.3; p = 0.029) and image quality score of small arteries below the knee (3.8 ± 0.2 vs. 3.1 ± 0.2; p = 0.001). Radiation dose was significantly lower in P2 than in P1 with CTDI_vol reduction of 40.9% (1.3 ± 0.1 vs. 2.2 ± 0.3 mGy; p = 0.006) and DLP reduction of 42.8% (148.7 ± 21.9 vs 260.2 ± 59.1 mGy * cm; p = 0.018).

CONCLUSION

Lower extremity CTA with DSCT flash caudo-cranial acquisition allows lower radiation dose with higher IVA, SNR, CNR and better image quality for small arteries below the knee than SSCT cranio-caudal acquisition.

CT Angiography of Peripheral Arterial Disease by 256-Slice Scanner: Accuracy, Advantages and Disadvantages Compared to Digital Subtraction Angiography

BACKGROUND

Peripheral arterial occlusive disease (PAOD) may cause disabling claudication or critical limb ischemia. Multidetector computed tomography (CT) technology has evolved to the level of 256-slice CT scanners which has significantly improved the spatial and temporal resolution of the images. This has provided the capability of chasing the contrast bolus at a fast speed enabling angiographic imaging of long segments of the body. These images can be reconstructed in various planes and various modes for detailed analysis of the peripheral vascular diseases which helps in making treatment decision.

PURPOSE

The aim of this retrospective study was to compare the CT angiograms (CTAs) of all cases of PAOD done by 256-slice CT scanner at a tertiary care vascular center and comparing these images with the digital subtraction angiograms (DSAs) of these patients.

MATERIALS AND METHODS

The retrospective study included 53 patients who underwent both CTA and DSA at our center over a period of 3 years from March 2013 to March 2016.

RESULTS

The CTA showed high sensitivity (93%) and specificity (92.7%) for overall assessment of degree of stenosis in a vascular segment in cases of aortic and lower limb occlusive disease. The assessment of lesions of infrapopliteal segment was comparatively inferior (sensitivity 91.6%, accuracy 73.3%, and positive predictive value 78.5%), more so in the presence of significant calcification. The advantages of CTA were its noninvasive nature, ability to image large area of body, almost no adverse effects to the patients, and better assessment of vessel wall disease. However, the CTA assessment of collaterals was inferior with a sensitivity of only 62.7% as compared to DSA. Overall, 256-slice CTA provides fast and accurate imaging of vascular tree which can restrict DSA only in few selected cases as a problem-solving tool where clinico-radiological mismatch is present.

Pulse Waves in the Lower Extremities as a Diagnostic Tool of Peripheral Arterial Disease and Predictor of Mortality in Elderly Chinese

Patients with peripheral arterial disease may have elongated upstroke time in pulse waves in the lower extremities. We investigated upstroke time as a diagnostic tool of peripheral arterial disease and predictor of mortality in an elderly (≥60 years) Chinese population. We recorded pulse waves at the left and right ankles by pneumoplethysmography and calculated the percentage of upstroke time per cardiac cycle. Diagnostic accuracy was compared with the conventional ankle-brachial index method (n=4055) and computed tomographic angiography (34 lower extremities in 17 subjects). Upstroke time per cardiac cycle at baseline (mean±SD, 16.4%±3.1%) was significantly ( P <0.0001) associated with ankle-brachial index in men (n=1803; r =−0.44) and women (n=2252; r =−0.32) and had an overall sensitivity and specificity of 86% and 80%, respectively, for the diagnosis of peripheral arterial disease (upstroke time per cardiac cycle, ≥21.7%) in comparison with computed tomographic angiography. During 5.9 years (median) of follow-up, all-cause and cardiovascular deaths occurred in 366 and 183 subjects, respectively. In adjusted Cox regression analyses, an upstroke time per cardiac cycle ≥21.7% (n=219; 5.4%) significantly ( P <0.0001) predicted total and cardiovascular mortality. The corresponding hazard ratios were 1.98 (95% confidence interval, 1.48–2.65) and 2.29 (1.58–3.32), respectively, when compared with that of 2.10 (1.48–3.00) and 2.44 (1.57–3.79), respectively, associated with an ankle-brachial index of ≤0.90 (n=115; 2.8%). In conclusion, pulse waves in the lower extremities may behave as an accurate and ease of use diagnostic tool of peripheral arterial disease and predictor of mortality in the elderly.

Automatic scan triggering software "confused": Computed tomography angiography in foot arteriovenous malformation!

Multidetector computed tomography angiography (MDCTA) has become a well-established modality for limb angiography for a variety of indications. The technique of MDCTA depends on the scanner features including the number of detector rows, rotation speeds and single or dual source energy. Integral to a diagnostic quality CTA is the acquisition timing. Various techniques are available for determining the appropriate timing of scan acquisition which includes fixed delay, test bolus and the bolus tracking technique. The transit times of contrast from the aorta to the peripheral arteries shows a wide variability and is dependent upon the inter individual hemodynamic states. The bolus tracking technique is the most preferred one which allows reliable scan timing with acceptable contrast volume and radiation dose. Pitfalls with all these techniques are well described and we report one such technical pitfall in a case of left foot arteriovenous malformation (AVM) where the bolus tracking technique employed for scan triggering failed to initiate acquisition.

Tissue engineered vascular grafts--preclinical aspects

Tissue engineering enables the development of fully biological vascular substitutes that restore, maintain and improve tissue function in a manner identical to natural host tissue. However the development of the appropriate preclinical evaluation techniques for the generation of fully functional tissue-engineered vascular graft (TEVG) is required to establish their safety for use in clinical trials and to test clinical effectiveness. This review gives an insight on the various preclinical studies performed in the area of tissue engineered vascular grafts highlighting the different strategies used with respect to cells and scaffolds, typical animal models used and the major in vivo evaluation studies that have been carried out. The review emphasizes the combined effort of engineers, biologists and clinicians which can take this clinical research to new heights of regenerative therapy.

Technical considerations for lower limb multidetector computed tomographic angiography

Multidetector computed tomography (MDCT) enables imaging of the entire arterial tree non-invasively. Optimal technical considerations for performing MDCT angiography (MDCTA) are essential for accurate diagnosis and atherosclerotic disease stratification. This review article focuses on the various technical aspects necessary for peripheral computed tomographic angiography (CTA) acquisition. Common clinical indications for peripheral MDCTA and the latest scan protocols are described. The essential issue of radiation dose reduction is discussed, along with methods of optimal contrast bolus detection and delivery. Post-processing techniques are also presented. Previously, digital subtraction angiography was the only established reliable imaging technique to quantify atherosclerotic disease load; however, MDCTA may now challenge this old gold standard, along with other non-invasive techniques such as magnetic resonance angiography (MRA).

Value of MDCT angiography in developing treatment strategies for critical limb ischemia

OBJECTIVE

The purpose of this study was to assess the value of MDCT angiography in the development of strategies for the treatment of patients with critical limb ischemia.

MATERIALS AND METHODS

During a 12-month period, 150 patients were referred to our department for CT angiography of the peripheral arteries. All patients (n = 28) with clinical stage IV peripheral arterial occlusive disease were included in this retrospective study. The treatment reports, discharge summaries, and follow-up examinations were reviewed to ascertain the number of patients correctly treated on the basis of the CT angiographic findings.

RESULTS

After CT angiography, endovascular treatment was indicated for eight patients, surgical revascularization for four patients, and a combined endovascular and surgical approach for two patients. That the correct treatment decision had been made in all 14 cases was confirmed on the basis of successful endovascular or surgical revascularization. In eight patients, medical treatment was indicated, and one patient underwent amputation at the level of the thigh. Five patients were referred for complementary digital subtraction angiography, but no additional findings were made. During follow-up, three of the original 28 patients were in grave general condition and died within 7 weeks after CT angiography. Thirteen patients needed no additional treatment during the follow-up period through January 2008. After a median treatment-free interval of 381 days, 12 patients underwent additional revascularization because of clinical progression of disease.

CONCLUSION

MDCT angiographic findings lead to accurate recommendations for the management of critical limb ischemia. Thus CT angiography seems to be an important technique for the management of stage IV peripheral arterial occlusive disease in patients without absolute contraindications to CT angiography.

Assessment of aortic pathology and peripheral arterial disease using multidetector computed tomographic angiography

The development of multidetector computed tomography represents a remarkable diagnostic advancement because this imaging modality has been widely used in the evaluation of the cardiovascular system. With scanner-adjusted image acquisition and contrast medium administration, multidetector computed tomographic angiography provides a cost-effective and accurate imaging assessment in patients with aortic pathologies or peripheral arterial occlusive disease. Multidetector computed tomographic angiography is associated with several advantages, including high image spatial resolution and rapid imaging acquisition speed. This diagnostic methodology allows accurate detection of a variety of intravascular lesions in the carotid artery, thoracic and abdominal aorta, renal arteries, and peripheral arterial systems. This article provides an overview of multidetector computed tomographic angiography in the assessment of arterial disease and reviews current literature about this diagnostic technology in the evaluation of aortic and peripheral arterial pathologies.

Limitations of and Lessons Learned from Clinical Experience of 1,020 Duplex Arteriography

Objective: Due to the inherent risks, deficiencies and cost associated with contrast arteriography (CA), our group has been utitilizing duplex arteriography (DA) for evaluating the arteries of the lower extremity for patients undergoing lower extremity revascularization. In an effort to further explore the strengths and weaknesses of DA, we reviewed our evolving experience with DA from January 1, 1998, to January 1, 2005.

Patients and Methods: The arterial segments starting from mid-abdominal aorta to the pedal arteries were studied in cross-sectional and longitudinal planes using a variety of scanheads of 7–4, 10–5, 12–5, 5–2 and 3–2 MHz extended operative frequency range to obtain high-quality B-mode, color and power Doppler images as well as velocity spectra. In 906 patients, 1,020 duplex arteriograms were obtained. The ages ranged from 30–98 years old with a mean of 73±11 (SD) years. Fifty percent of the patients were diabetics. Indications for the examination included: tissue loss (409), rest pain (221), claudication (310), acute ischemia (74), popliteal aneurysm (45), SFA aneurysm (2), abdominal aortic aneurysms (AAA) (10) and failing bypass (55). Prior procedures had been performed in 262. DA was performed by six technologists (4 of whom are MDs). In all, 207 DA were performed intraoperatively and the remainder, preoperatively.

Results: The resultant procedures based upon DA included: bypass to the popliteal artery (262) and bypass to an infrapopliteal artery (325), endovascular procedures (363), thrombectomy (11), embolectomy (9), inflow bypass procedures to the femoral arteries (46), débridment (4), amputation (8) and no intervention (75). The areas not visualized well included: iliac (73), femoral (26), popliteal (17), and infrapopliteal (221). Additional imaging after DA was deemed necessary in 102 cases to obtain enough information to plan lower extremity revascularization. Factors associated with increased need to obtain CA included: DM ( p<.001), infrapopliteal calcification ( p<.001), older age ( p = .01) and limb threatening ischemia ( p<.001). Factors not associated with the need to obtain CA included: which technologist performed the exam, whether the technologist has a medical degree and whether the patient underwent prior revascularization.

Conclusions: In 90% of patients reviewed, DA is able to obtain the needed information to plan lower extremity revascularization. Severe tibial vessel calcification is the most common cause of an incomplete DA exam and determines when alternative imaging modalities need to be obtained.

Multidetector computed tomographic angiography of the cardiovascular system

The introduction of multidetector computed tomography (MDCT) is considered a dramatic development in CT imaging that has direct implication in the imaging of various systems, in particular the cardiovascular system. The advantages of MDCT are an enormous increase in imaging acquisition speed, more coverage of the patient, and high spatial resolution. This article reviews the recent developments in CT angiography and discusses the clinical application relevant to diagnosis and endovascular treatment of cardiovascular diseases.

Advances in vascular imaging

Advances in vascular surgery have mirrored advances in diagnostic imaging. Indeed, the endovascular revolution has been made possible largely by advances in computed tomography, magnetic resonance imaging, and vascular ultrasound. As technology allows better noninvasive vascular diagnosis, conventional angiography, once the gold standard for the diagnosis of vascular disease, is now reserved largely for intervention. This article discusses the current state of vascular imaging. Specific emphasis is placed on the comparative clinical utility of different imaging modalities in the detection and management of vascular disease.

Effect of MDCT angiographic findings on the management of intermittent claudication

OBJECTIVE

The purpose of this study was to assess the reliability of treatment decisions based on MDCT angiographic findings of stage IIb peripheral arterial occlusive disease (PAOD).

MATERIALS AND METHODS

Fifty-eight patients with stage IIb PAOD underwent CT angiography of the abdominal aorta and runoff vessels for further treatment planning. Treatment reports, discharge summaries, and follow-up examinations were reviewed to determine the number of treatments correctly planned on the basis of CT angiographic findings.

RESULTS

On the basis of CT angiographic findings, endovascular treatment was indicated for 18 patients, surgical revascularization for nine patients, and a combined endovascular and surgical approach for two patients. Conservative treatment was indicated for 29 patients. On the basis of successful revascularization, the correctness of the treatment decision was confirmed in all but one patient (n = 28). The treatment plan was modified for one patient referred for surgical revascularization. In that patient, stenosis of the common femoral artery had been overlooked on CT angiography. Patients for whom conservative management was indicated on the basis of CT angiographic findings (n = 29) had a mean follow-up period of 501 days without needing revascularization treatment. This result was defined as indirect confirmation of the accuracy of the decision made with CT angiography.

CONCLUSION

The findings on MDCT angiography led to correct treatment recommendations for patients with claudication. Thus, CT angiography should be used in the management of PAOD.

Multi-detector row computed tomography angiography of peripheral arterial disease

With the introduction of multi-detector row computed tomography (MDCT), scan speed and image quality has improved considerably. Since the longitudinal coverage is no longer a limitation, multi-detector row computed tomography angiography (MDCTA) is increasingly used to depict the peripheral arterial runoff. Hence, it is important to know the advantages and limitations of this new non-invasive alternative for the reference test, digital subtraction angiography. Optimization of the acquisition parameters and the contrast delivery is important to achieve a reliable enhancement of the entire arterial runoff in patients with peripheral arterial disease (PAD) using fast CT scanners. The purpose of this review is to discuss the different scanning and injection protocols using 4-, 16-, and 64-detector row CT scanners, to propose effective methods to evaluate and to present large data sets, to discuss its clinical value and major limitations, and to review the literature on the validity, reliability, and cost-effectiveness of multi-detector row CT in the evaluation of PAD.

The role of CT and MRI in the assessment of peripheral vascular disease

Atherosclerosis is a serious health problem in developed countries and the main cause of morbidity and mortality. Treatment strategies such as surgical procedures, percutaneous catheter-based interventions or pharmacologic options depend on the accurate classification of atherosclerotic disease with respect to location, extent, and severity of arterial involvement. For this purpose, several imaging techniques are in clinical use. Due to recent improvements in scanner technology, noninvasive imaging modalities are now widely available for evaluating atherosclerotic lesions throughout the body. This article focuses on the clinical role of these imaging modalities in the assessment of peripheral vascular disease, including the aorta and extracranial arteries.

Multi-slice CT (MSCT) angiography for assessment of traumatic lesions of lower limbs peripheral arteries

AIM

The aim of this study was to evaluate the feasibility and effectiveness of multi-slice computed tomography (MSCT) angiography for the assessment of traumatic lesions involving the arteries of the lower limbs.

MATERIALS AND METHODS

Forty-seven patients with suspected arterial post-traumatic lesions of lower limbs underwent MSCT angiography (4 x 2.5-mm collimation, 3-mm slice width). The standards of reference were: digital subtraction angiography (DSA; patients with inconclusive/doubtful or positive MSCT angiography indicating a need for intravascular treatment), surgical findings (patients with positive MSCT angiography indicating a need for surgery), or clinical/investigational follow-up (patients with negative MSCT angiography and no need for further diagnostic procedures or surgery).

RESULTS

All CT exams were technically adequate. Sensitivity, specificity, and overall diagnostic accuracy of MSCT angiography were 96.3, 90, and 93.6%, respectively, relative to the reference of standard findings. In 44 out of 47 patients, MSCT angiography allowed a correct continuation of the diagnostic work-up.

CONCLUSION

MSCT angiography is a reliable fast tool for diagnosing traumatic vascular lesions, providing results comparable to DSA.

[Abdominal aortic aneurysm and renovascular disease]

Recent technological advances in the diagnosis and therapy of abdominal aortic aneurysm and renovascular disease are continuing to bring about changes in the way patients suffering from these conditions are treated. The prevalence of both these conditions is increasing. This is due to greater life-expectancy in patients with arteriosclerosis, a pathogenetic factor underlying both conditions. The application of diagnostic imaging techniques to non-vascular conditions has led to the early diagnosis of abdominal aortic aneurysm. Clinical suspicion of reno-vascular disease can be confirmed easily using high-resolution diagnostic imaging modalities such as CT angiography and magnetic resonance angiography. Endovascular intervention is successfully replacing conventional surgical repair techniques, with the result that it may be possible to improve outcome in both conditions using effective and minimally invasive approaches. Future technological developments will enable these endovascular techniques to be applied in the large majority of patients with abdominal aortic aneurysm or renovascular disease.

Use of intra-arterial multi-detector row CT angiography for the evaluation of an ischaemic limb in a patient with renal impairment

The vastly improved scanning speed and z-axis resolution afforded by multi-detector technology has allowed CT to refine its traditional roles and to explore many new applications in imaging. We present a case report of a patient with renal failure and an ischaemic leg, which illustrates a useful new CT vascular imaging application. By carrying out 16-channel multi-detector row CT angiography through a sheath introduced into the common femoral artery, we obtained a high-quality angiographic image of the affected leg, using only 30 mL of iodinated contrast material. The examination definitively showed the number, distribution and patency of the tibial run-off arteries, with significant influence on the patient's subsequent clinical management. This simple and relatively minimally invasive technique is useful in peripheral vascular imaging, when conventional CT angiography using a large volume of i.v. contrast and MR angiography are unsuitable or unavailable.

CT angiography of peripheral arterial disease

Lower-extremity computed tomographic (CT) angiography (ie, peripheral CT angiography) is increasingly used to evaluate patients with peripheral arterial disease. It is therefore increasingly important for all vascular specialists to become familiar with the strengths and limitations of this new technique. The aims of this review are to explain the principles of scanning and injection technique for a wide range of CT scanners, to explain and illustrate the properties of current image postprocessing tools for effective visualization and treatment planning, and to provide an overview of current clinical applications of peripheral CT angiography.

CT angiography of peripheral arterial bypass grafts: Accuracy and time-effectiveness of quantitative image analysis with an automated software tool

RATIONALE AND OBJECTIVES

Qualitative analysis of computed tomography (CT) angiography data often is limited by intra- and interobserver variability. The purpose of this study was to evaluate the time-effectiveness and accuracy of a quantitative CT angiography data analysis using automated software in comparison with qualitative axial and coronal CT image reading in patients with peripheral bypass grafts.

MATERIALS AND METHODS

Twenty-eight patients with 33 saphenous bypass grafts underwent 4-channel (n = 21) and 16-channel (n = 7) CT angiography. Two readers evaluated in consensus the CT data qualitatively on axial and coronal reconstructions and with the software regarding the presence of graft stenoses, aneurysmal changes, and arteriovenous fistulas. The time for data analysis was taken and the accuracy was compared with the results from digital subtraction angiography (DSA).

RESULTS

No significant difference was present between data analysis time using axial and coronal CT images (4.9 +/- 1.5 minutes) and when using the software tool (5.5 +/- 1.4 minutes). Good (kappa = 0.652) to excellent (kappa = 1.000) intermodality agreement was present between qualitative and quantitative CT analysis regarding graft-related abnormalities. Sensitivity and specificity for diagnosing stenoses, aneurysms, and fistula did not differ significantly (P > .025) between qualitative CT image reading and the automated software tool.

CONCLUSIONS

CT angiography analysis of peripheral bypass grafts using an automated software tool is similar regarding time-effectiveness and accuracy when compared with qualitative CT data analysis on axial and coronal images. It may assist in determining the significance of an abnormality and can yield objective morphometric data of vessel calibers.

MDCT angiography for evaluation of the complete vascular tree of hemodialysis fistulas

OBJECTIVE

The purpose of our study was to assess the clinical feasibility of MDCT angiography for evaluating hemodialysis arteriovenous fistulas (AVFs).

MATERIALS AND METHODS

MDCT angiography of the complete vascular trees of 36 failing AVFs or AVF-related complications (20 native and 16 polytetrafluoroethylene graft AVFs) was reviewed. The numbers and degrees of stenoses at the anastomoses, graft loops, and draining and central veins and the presence of aneurysms or thrombosis were recorded. Wilcoxon's signed rank test was used to compare the findings of MDCT angiography with those of digital subtraction angiography (DSA) (n = 10), surgery (n = 22), or both (n = 4) performed within 2-6 days. Kappa statistics were used to correlate the clinical feasibility of MDCT angiography assessed by two reviewers.

RESULTS

Among the 14 AVFs examined with both MDCT angiography and DSA, no significant difference was seen in the detection and grading (p = 0.317 to > 0.999) of stenoses at various segments of the entire vascular tree. Among the 36 AVFs examined, MDCT angiography also showed no significant difference from DSA or surgery in revealing vascular stenoses, aneurysms, and thromboses from the supplying artery to central veins (p = 0.317 to > 0.999). Overall, the sensitivity, specificity, positive and negative predictive values, and accuracy of MDCT angiography in lesion detection were 98.7%, 97.5%, 98.8%, 97.2%, and 98.3%, respectively. High image quality with superb interobserver correlation (kappa = 0.809 to > 0.999) validated the clinical feasibility of MDCT angiography for assessing AVFs.

CONCLUSION

MDCT angiography is clinically feasible for evaluating the complete vascular tree of failing AVFs and in showing uncommon complications, including brachial aneurysms and central vein lesions.

IV Contrast Selection for MDCT: Current Thoughts and Practice

OBJECTIVE

The purpose of this article is to review studies evaluating how contrast concentration affects MDCT of the body and to report IV contrast infusion protocols from MDCT angiography and MDCT of abdominal tumors.

CONCLUSION

Higher concentrations (350 mg I/mL or greater) may improve visualization of small abdominal arteries. However, preliminary data comparing 300 mg I/mL to higher concentrations for MDCT of hypervascular hepatocellular carcinoma and pancreatic cancer have shown that higher concentrations may not increase tumor conspicuity.

Angiographic imaging of the lower extremities with multidetector CT

Multidetector CT (MDCT) has improved imaging of the arteries in the lower extremities. The main advantages of this novel technology are the exceptionally fast scan times, high spatial resolution, increased anatomic coverage, and capability to generate high-quality multiplanar reformations and three-dimensional (3-D) renderings from raw data that can be reprocessed easily and quickly. The applications of MDCT in imaging the lower extremities are multiple and varied. They include the evaluation of peripheral arterial occlusive and aneurysmal disease, the patency and integrity of bypass grafts, and arterial injury owing to trauma. This article describes the techniques of lower extremity MDCT angiography and its use in a few clinical applications.

Hemodialysis Fistula Occlusion

The speed and resolution of 64-slice CT have resulted in new applications for CT angiography (CTA) owing to rapid data acquisition during the arterial phase, improved visualization of small vessels, and lengthened anatomic coverage. Extremity CT angiography is one such region. This case report shows the utility of multislice CTA for the evaluation of hemodialysis graft dysfunction.

Sixteen–Detector Row CT Angiography for Lower-Leg Arterial Occlusive Disease: Analysis of Section Width

Institutional review board approval and written informed consent from all patients were obtained. Diagnostic accuracy of three reconstructions of 16-detector row computed tomographic (CT) angiography data with different section widths and increments (2.0 and 1.0 mm [CT data set 1], 1.0 and 0.5 mm [CT data set 2], and 0.75 and 0.4 mm [CT data set 3]) was compared with that of digital subtraction angiography (DSA) in 163 arterial segments in 17 patients with occlusive peripheral arterial disease (PAD). Arterial visibility was superior with CT as compared with DSA (P < .008). Sensitivity for stenosis detection did not differ between the CT reconstructions, whereas specificity was significantly improved when CT data set 3 was used (P < .017). Stenosis length did not differ significantly between CT angiography and DSA. Accuracy of stenosis detection was 88.2%, 90.8%, and 96.1% with CT data sets 1, 2, and 3, respectively. CT angiography has excellent diagnostic accuracy in the assessment of lower-leg PAD provided that the thinnest possible section width is used.

Aorto-iliac multidetector-row CT angiography with low kV settings: improved vessel enhancement and simultaneous reduction of radiation dose

The aim of the study was to implement an abdominal CT angiography protocol using 100 kVp and to compare SNR and CNR, as well as subjective image quality, to a standard CT angiography protocol using 120 kVp on a 16 detector-row CT scanner. Forty-eight patients were referred for routine abdominal CT angiography on a 16 detector-row CT scanner. Patients were scanned using either 120 or 100 kVp at constant mAs settings. Vessel opacification was provided by automated contrast injection using similar injection protocols. Density measurements were performed along the aorto-iliac axis with SNR and CNR calculation. In addition, the estimated effective patient radiation dose was calculated. Results of both protocols were compared. The 100-kVp protocol (432+/-80 HU) showed a significantly higher vessel density than the 120-kVp (333+/-90 HU; P<0.001) protocol, corresponding to an average increase in signal intensity of 30.7%. SNR (36.0 vs 37.0) and CNR (31.1 vs 31.7) for the 100-kV protocol were not significantly lower that those for the standard protocol (P=0.79 and P=0.87), whilst the average estimated dose was significantly lower using the 100-kVp protocol (6.7+/-0.4 vs 10.1+/-1.2 mSv; P<0.0001). Tube kVp reduction from 120 to 100 kVp allows for significant reduction of patient dose in abdominal CT angiography, without significant change in SNR,CNR and image quality.

Magnetic Resonance Angiography in the Follow-up of Distal Lower-Extremity Bypass Surgery: Comparison with Duplex Ultrasound and Digital Subtraction Angiography

PURPOSE

The danger of limb loss as a consequence of acute occlusion of infrapopliteal bypasses underscores the requirement for careful patient follow-up. The objective of this study was to determine the agreement and accuracy of contrast material-enhanced moving-table magnetic resonance (MR) angiography and duplex ultrasonography (US) in the assessment of failing bypass grafts. In cases of discrepancy, digital subtraction angiography (DSA) served as the reference standard.

MATERIALS AND METHODS

MR angiography was performed in 24 consecutive patients with 26 femorotibial or femoropedal bypass grafts. Each revascularized limb was divided into five segments--(i) native arteries proximal to the graft; (ii) proximal anastomosis; (iii) graft course; (iv) distal anastomosis; and (v) native arteries distal to the graft-resulting in 130 vascular segments. Three readers evaluated all MR angiograms for image quality and the presence of failing grafts. The degree of stenosis was compared to the findings of duplex US, and in case of discrepancy, to DSA findings. Two separate analyses were performed with use of DSA only and a combined diagnostic endpoint as the reference standard.

RESULTS

Image quality was rated excellent or intermediate in 119 of 130 vascular segments (92%). Venous overlay was encountered in 26 of 130 segments (20%). In only two segments was evaluation of the outflow region not feasible. One hundred seventeen of 130 vascular segments were available for quantitative analysis. In 109 of 117 segments (93%), MR angiography and duplex US showed concordant findings. In the eight discordant segments in seven patients, duplex US overlooked four high-grade stenoses that were correctly identified by MR angiography and confirmed by DSA. Percutaneous transluminal angioplasty was performed in these cases. In no case did MR angiography miss an area of stenosis of sufficient severity to require treatment. Total accuracy for duplex US ranged from 0.90 to 0.97 depending on the reference standard used, whereas MR angiography was completely accurate (1.00) regardless of the standard definition.

CONCLUSION

Our data strongly suggest that the accuracy of MR angiography for identifying failing grafts in the infrapopliteal circulation is equal to that of duplex US and superior to that of duplex US in cases of complex revascularization. MR angiography should be included in routine follow-up of patients undergoing infrapopliteal bypass surgery.

Determination of Cardiac Output With Multislice Spiral Computed Tomography

OBJECTIVE

To validate and to determine the reproducibility of cardiac output (CO) measurements based on a test-bolus examination in multislice spiral computed tomography (MSCT) in comparison with invasively measured CO using the thermal dilution technique.

MATERIAL AND METHODS

In 8 swine, CO was determined by invasive thermal dilution technique and by analysis of enhancement data from dynamic MSCT test-bolus examinations. To assess reproducibility, all MSCT examinations were performed twice. Results were compared using Pearson's correlation coefficient and Bland-Altman plots.

RESULTS

Measure by thermal dilution technique CO was 3.71 +/- 1.12 L/min, whereas CO was 3.67 +/- 1.30 L/min using MSCT. Pearson's correlation coefficient was 0.89. The average deviation between MSCT and thermal dilution technique was 0.04 L/min with a standard deviation of 0.59 L/min. There was a good agreement between both MSCT measurements with a mean deviation of -0.03 L/min and a standard deviation of 0.51 L/min.

CONCLUSION

CO can reliably be determined from MSCT by means of indicator dilution technique. Measurements are reproducible and provide valuable information on the overall cardiovascular performance without application of additional contrast material or radiation. As this technique does not require time-consuming postprocessing it can be added to routine reporting.

Basics of computed tomography angiography of the lower extremity vessels

Complete noninvasive, angiographic evaluation of the abdominal aorta and lower extremity vessels using the latest generation of multidetector row computed tomography (CT) scanners can now be accomplished in a single scan lasting less than a minute. The high spatial resolution of these new scanners and their more efficient use of contrast permit accurate depiction of disease in the smaller tibial and pedal vessels, as well as the larger diameter iliac and femoral arteries; nevertheless, many challenges and obstacles remain to its more widespread acceptance. Foremost among these, is the difficulty in accurately reconstructing the smaller leg and pedal vessels from individual CT slices, a process that must to a very great extent be done manually, and the potential nephrotoxicity of iodinated contrast material. Future advances in imaging software that could more fully automate accurate three-dimensional reconstructions of the lower extremity vasculature, and detector technology to allow for even finer resolution of the vasculature will further enhance an already powerful and clinically useful tool.

MDCT-imaging of peripheral arterial disease

With the design and development of advanced computed tomography (CT) techniques and applications, like the newest generation of 16-detector-row CTs, CT angiography of the lower limb becomes a feasible tool for imaging peripheral vascular disease. Due to several advantages, compared with conventional digital subtraction angiography (DSA), including minimal invasiveness, CT angiography competes against diagnostic DSA in several clinical situations. 16-DCT offers the possibility to acquire thin slices from the diaphragm to the ankle in less than 40 sec. Easily, a data set of 800 to 1200 transverse slices may be created. To use transverse reconstructions alone to read these volumetric data sets is not appropriate. Powerful post-processing tools for volumetric analysis are required so that routine interpretation can be performed as efficiently and accurately as transverse section review. Because of its widespread availability and applicability, CT angiography of the lower extremities may be applied to patients in a pre- or post-procedural situation and also serves as a first line modality in patients with acute onset of clinical symptoms. Although multidetector CT arteriography is rapidly achieving clinical acceptance, further studies need to be performed to fully evaluate the clinical value of this method of peripheral arterial imaging. This article reviews the current status of multidetector CT peripheral arteriography, including indications, technical details, image post-processing, radiation exposure, and clinical results.