Technical considerations for lower limb multidetector computed tomographic angiography

Evaluation of Soft-Tissue Hematomas With Real-Time, Contrast-Enhanced Ultrasound: A Pilot Study With Preliminary Findings

ABSTRACT

In this study, we investigated the feasibility of using contrast-enhanced ultrasound (CEUS) to detect active hemorrhage in patients presenting with soft-tissue hematomas. Adult patients with clinically suspected, actively bleeding hematomas were prospectively enrolled. Contrast-enhanced ultrasound was used to assess for contrast extravasation. Ultrasound results were compared with those of multidetector computed tomographic (MDCT) imaging, operative findings, and clinical course. Sixteen patients (9 women, 7 men; mean age, 69 [SD, 13] years) were enrolled. Thirteen patients underwent MDCT imaging during their initial visit, and for 11, CEUS and computed tomography (CT) findings were concordant. The remaining patients had a negative CEUS study that was consistent with their clinical course. In 8 patients, CT imaging showed active extravasation (6 arterial, 1 indeterminate, 1 slow venous). Contrast-enhanced ultrasound and CT findings were concordant for all cases of arterial bleeding. For 1 patient, CEUS provided superior diagnostic information by identifying a pseudoaneurysm. The 2 discrepant patient cases had a ≥3-hour delay between CT and CEUS, and in 1 patient, CEUS was limited by body habitus. The second patient had no active bleeding identified in the operating room. Compared with CT, CEUS had a sensitivity and specificity of 75% and 100%, respectively, and positive and negative predictive values were 100% and 71%, respectively. Diagnostic accuracy was 85% in this limited study. Contrast-enhanced ultrasound is a promising alternative to MDCT in select patients and may sometimes provide superior clinical information. Limiting factors are large hematoma size, unfavorable anatomic location, and body habitus.

Lower extremity CT angiography in peripheral arterial disease: from the established approach to evolving technical developments

With the advent of multidetector computed tomography (CT), CT angiography (CTA) has gained widespread popularity for noninvasive imaging of the arterial vasculature. Peripheral extremity CTA can nowadays be performed rapidly with high spatial resolution and a decreased amount of both intravenous contrast and radiation exposure. In patients with peripheral artery disease (PAD), this technique can be used to delineate the bilateral lower extremity arterial tree and to determine the amount of atherosclerotic disease while differentiating between acute and chronic changes. This article provides an overview of several imaging techniques for PAD, specifically discusses the use of peripheral extremity CTA in patients with PAD, clinical indications, established technical considerations and novel technical developments, and the effect of postprocessing imaging techniques and structured reporting.

Quick evaluation of lower leg ischemia in patients with peripheral arterial disease by time maximum intensity projection CT angiography: a pilot study

Background

The purpose of this study is to evaluate a new method involving time maximum intensity projection (t-MIP) postprocessed from dynamic computed tomographic angiography (dyn-CTA) in diagnosing peripheral arterial disease (PAD).

Methods

A population of 34 patients with known PAD was examined with a combined CTA protocol consisting of a standard CTA (s-CTA) scan of the lower extremities and a dyn-CTA scan of the calves. For each lower leg, t-MIP images consisting of the MIP₀ (sagittal MIP), MIP_+θ (45° lateral MIP), and MIP_−θ (− 45° lateral MIP) were automatically generated from dyn-CTA. An objective evaluation of the vascular CT attenuation of the best enhancement phase of dyn-CTA and t-MIP was measured; a subjective evaluation of vessel stenosis and occlusion was performed, assigning a score for t-MIP and s-CTA. The CT attenuation of t-MIP and dyn-CTA was compared, as were the runoff scores of t-MIP and s-CTA.

Results

The CT attenuation of t-MIP CTA of three vascular segments from 68 lower extremities was higher than that of the best enhancement phase of dyn-CTA and s-CTA, with statistically significant differences at the posterior tibial artery and fibular artery (all p < 0.05). There were strong correlations (r ≥ 0.75, p < 0.05) of the runoff scores between t-MIP and s-CTA.

Conclusions

There is potential clinical applicability of t-MIP in assisting with the diagnosis of lower leg vascular stenosis in dyn-CTA with reliable diagnostic accuracy and convenient immediacy.

Over-utilization of computed tomography angiography in extremity trauma

Objectives:

Widespread availability of computed tomography angiography (CTA) for diagnosing arterial injury in injured extremities has created the possibility of overuse. The objective of this study was to evaluate CTA utilization, indications, ordering personnel, and rate of significant findings for blunt or penetrating extremity trauma at a level I trauma center.

Methods:

We performed a retrospective chart review of 1440 consecutive CTAs of upper and lower extremities from 2010 to 2012 at a large level I trauma center, and included only those done for acute trauma. Data were collected with regard to injury, initial exam, reason given for ordering a CTA, specialty of physician ordering CTA, results, and vascular interventions needed. CTAs were categorized as appropriately ordered based on if there was a documented abnormal distal pulse or ankle-brachial index (ABI). Study indication was classified as inconclusive if no vascular exam was documented or physical exam varied.

Results:

A total of 481 CTAs were performed after blunt or penetrating trauma in the emergency room with 31.0% appropriately indicated, 48.0% without indication, and 21.8% inconclusive. Mechanism of injury was most commonly a gunshot wound (40.3%), followed by motor vehicle accidents (39.5%). Overall, 61.5% of the studies had normal arterial flow and only 15.8% of CTAs required vascular operative intervention. Of the studies appropriately indicated, 76.5% had positive findings, with 43% needing operative intervention compared to the inappropriately indicated studies only 11.6% had positive findings, with 0.4% needing operative intervention (P < .0001).

Conclusion:

CTA for blunt or penetrating trauma at a level I trauma center may be over-utilized. Often, this advanced imaging is ordered prior to orthopaedic evaluation or limb reduction, without exam-based indication, and most do not affect patients’ treatment. From our study, CTA utilization based on more stringent exam findings at our hospital could eliminate 48% of all CTA studies for trauma.

Role of lower extremity run-off CT angiography in the evaluation of acute vascular disease

In the acute care setting, radiologists are frequently asked to assist in the evaluation of patients presenting with signs and symptoms of lower extremity peripheral vascular disease. Non-traumatic peripheral vascular emergencies are most commonly the result of thrombosis, either in a native vessel or within a bypass graft or stent. Arterial emboli, peripheral aneurysm with embolus or thrombosis, and direct arterial trauma are additional, less common causes. Traumatic peripheral vascular emergencies include vessel occlusion, transection, pseudoaneurysms, active extravasation, and arteriovenous fistulas. The high morbidity and mortality associated with acute limb ischemia makes rapid diagnosis and early initiation of therapy critical in the management of such patients. Computed tomographic angiography (CTA) offers the vascular specialist a rapid, widely available, and accurate means to diagnose and grade the extent of vascular disease in the acute care setting. In this pictorial essay, the key elements of lower extremity run-off CTA are reviewed, including relevant anatomy, imaging approach, and spectrum of imaging findings.

Advances in axial imaging of peripheral vascular disease

Peripheral artery disease (PAD) has become increasingly common in the US patient population and can be a highly symptomatic and significant source of morbidity. When PAD is suspected, the first-line screening study that is obtained is typically a noninvasive evaluation that includes the ankle brachial index (ABI). Following a positive screening study, invasive catheter digital subtraction angiography (DSA) has been historically used to image the peripheral artery system and still remains the gold standard. However, newer developments in axial imaging including computed tomography angiography (CTA) and magnetic resonance angiography (MRA) have in large part supplanted DSA for imaging the peripheral artery system in clinical practice. Benefits of CTA include rapid noninvasive acquisition, wide availability, high spatial resolution, and the ability to generate isotropic datasets on 64-detector row and higher CT scanners, thereby allowing for multiplanar 3D reformatting. Drawbacks of CTA include the exposure to both iodinated contrast and ionizing radiation, although the radiation dose exposure is lower than for DSA, and newer techniques such as using low tube voltage and rapid acquisition times allow for lower contrast doses. The presence of vascular calcification also limits the evaluation of small distal arteries using CTA, although the development of dual-energy CT techniques has significantly addressed this issue. Benefits of MRA include the avoidance of exposure to ionizing radiation and high diagnostic accuracy, while drawbacks include limited availability and increased cost along with the risk of nephrogenic systemic fibrosis that is associated with gadolinium-based contrast agents, although the latter can be mitigated by using newer non-contrast MR angiography techniques. Future technical advances in CT and MR hardware and software and MR pulse sequences will likely lead to the broader applicability and increased accuracy of noninvasive axial imaging in the evaluation of patients with peripheral artery disease.

Can Radiation Dose Be Reduced and Image Quality Improved With 80-kV and Dual-Phase Scanning of the Lower Extremities With 64-Slice Computed Tomography Angiography?

OBJECTIVE

To prospectively compare the new computed tomographic angiography (CTA) protocol (NCP) using 80-kV and dual-phase scanning with the routine CTA protocol (RCP) using 120-kV and single-phase scanning in patients with peripheral arterial disease.

METHODS

A total of 60 patients were randomized to undergo the NCP (30 patients) or RCP (30 patients) scan. We compared the arterial attenuation values, overriding of the contrast bolus, signal-to-noise ratio, and radiation dose between 2 groups.

RESULTS

The occurrence rate of contrast bolus overriding was not statistically significant (P = 0.69). The average arterial attenuation value in the NCP group was significantly higher (P < 0.05) than that in the RCP group. The radiation dose in the RCP group was significantly higher (P < 0.001) than that in the NCP group. The mean signal-to-noise ratio in the NCP group was significantly lower (P < 0.001).

CONCLUSIONS

Sixty-four-slice CTA with the NCP can significantly reduce the radiation dose and improve the arterial enhancement and calf arteries imaging.

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.

The gracilis myocutaneous free flap: a quantitative analysis of the fasciocutaneous blood supply and implications for autologous breast reconstruction

Background

Mastectomies are one of the most common surgical procedures in women of the developed world. The gracilis myocutaneous flap is favoured by many reconstructive surgeons due to the donor site profile and speed of dissection. The distal component of the longitudinal skin paddle of the gracilis myocutaneous flap is unreliable. This study quantifies the fasciocutaneous vascular territories of the gracilis flap and offers the potential to reconstruct breasts of all sizes.

Methods

Twenty-seven human cadaver dissections were performed and injected using lead oxide into the gracilis vascular pedicles, followed by radiographic studies to identify the muscular and fasciocutaneous perforator patterns. The vascular territories and choke zones were characterized quantitatively using the ‘Lymphatic Vessel Analysis Protocol’ (LVAP) plug-in for Image J® software.

Results

We found a step-wise decrease in the average vessel density from the upper to middle and lower thirds of both the gracilis muscle and the overlying skin paddle with a significantly higher average vessel density in the skin compared to the muscle. The average vessel width was greater in the muscle. Distal to the main pedicle, there were either one (7/27 cases), two (14/27 cases) or three (6/27 cases) minor pedicles. The gracilis angiosome was T-shaped and the maximum cutaneous vascular territory for the main and first minor pedicle was 35×19 cm and 34×10 cm, respectively.

Conclusion

Our findings support the concept that small volume breast reconstructions can be performed on suitable patients, based on septocutaneous perforators from the minor pedicle without the need to harvest any muscle, further reducing donor site morbidity. For large reconstructions, if a ‘T’ or tri-lobed flap with an extended vertical component is needed, it is important to establish if three territories are present. Flap reliability and size may be optimized following computed tomographic angiography and surgical delay.

Peripheral artery disease. Part 1: clinical evaluation and noninvasive diagnosis

Peripheral artery disease (PAD) is a marker of systemic atherosclerosis. Most patients with PAD also have concomitant coronary artery disease (CAD), and a large burden of morbidity and mortality in patients with PAD is related to myocardial infarction, ischemic stroke, and cardiovascular death. PAD patients without clinical evidence of CAD have the same relative risk of death from cardiac or cerebrovascular causes as those diagnosed with prior CAD, consistent with the systemic nature of the disease. The same risk factors that contribute to CAD and cerebrovascular disease also lead to the development of PAD. Because of the high prevalence of asymptomatic disease and because only a small percentage of PAD patients present with classic claudication, PAD is frequently underdiagnosed and thus undertreated. Health care providers may have difficulty differentiating PAD from other diseases affecting the limb, such as arthritis, spinal stenosis or venous disease. In Part 1 of this Review, we explain the epidemiology of and risk factors for PAD, and discuss the clinical presentation and diagnostic evaluation of patients with this condition.