Use of combined CT venography and CT pulmonary arteriography

Low-tube-voltage combined with adaptive statistical iterative reconstruction-V technique in CT venography of lower limb deep vein thrombosis

This study contains 2 arms: (1) the ASIR-V technique combined with low-tube-voltage in lower limb deep vein thrombosis (DVT) diagnosis was investigated; and (2) CT venography and ultrasound results in DVT diagnosis were compared. For arm 1, 90 patients suspected of DVT were randomly divided into 3 groups (30/group): groups A and B were scanned under 100-kV with pre-set ASIR-V weights of 30% and 50% respectively; group C were scanned under 70-kV with a 50% weight. For arm 2, 75 patients were divided into 3 groups (25/group), each group was CT scanned as in arm 1 and then all subjects were examined by ultrasound. Groups A, B and C had 16, 14 and 17 patients diagnosed with DVTs, respectively. There was no significant difference in subjective ratings of image quality among all groups. The 70-kV protocol remarkably increased venous attenuation value while all groups had similar DVT attenuation value. Higher noise was observed in group C, the CNR however, was actually augmented due to elevated venous attenuations. More importantly, group C had significantly lower CTDI_vol and DLP values. In conclusion, the 70-kV protocol is superior to the 100 kV protocols, which was supported by findings from the second arm study.

Advanced imaging in acute and chronic deep vein thrombosis

Deep venous thrombosis (DVT) affecting the extremities is a common clinical problem. Prompt imaging aids in rapid diagnosis and adequate treatment. While ultrasound (US) remains the workhorse of detection of extremity venous thrombosis, CT and MRI are commonly used as the problem-solving tools either to visualize the thrombosis in central veins like superior or inferior vena cava (IVC) or to test for the presence of complications like pulmonary embolism (PE). The cross-sectional modalities also offer improved visualization of venous collaterals. The purpose of this article is to review the established modalities used for characterization and diagnosis of DVT, and further explore promising innovations and recent advances in this field.

The diagnostic evaluation of pulmonary embolism

Due to the morbidity and mortality associated with either untreated disease or inappropriate anticoagulant therapy, accurate diagnosis of pulmonary embolism is essential. Pulmonary angiography, the current gold standard test for diagnosing pulmonary embolus, is both invasive and costly; therefore, noninvasive diagnostic strategies have been developed. Noninvasive tests often have to be combined to either raise the posttest probability of disease to a level justifying treatment or lower it to a level at which withholding treatment is warranted. Diagnostic algorithms involving clinical assessment; venous ultrasonography; D-dimer testing; ventilation-perfusion lung scanning; and, more recently, computed tomography have been validated in management trials of patients with a suspected pulmonary embolism. The optimal strategy at individual institutions is dependent on local availability, expertise, and cost. Magnetic resonance imaging and combined computed tomographic pulmonary angiography and venography possess the potential to be used as stand-alone tests for pulmonary embolism but require further evaluation.

Impact of a rapid rule-out protocol for pulmonary embolism on the rate of screening, missed cases, and pulmonary vascular imaging in an urban US emergency department

STUDY OBJECTIVE

This study tests the hypothesis that implementation of a point-of-care emergency department (ED) protocol to rule out pulmonary embolism would increase the rate of evaluation without increasing the rate of pulmonary vascular imaging or ED length of stay and that less than 1.0% of patients with a negative protocol would have an adverse outcome.

METHODS

A baseline study was conducted on patients with suspected pulmonary embolism at an urban ED to establish baseline measurements performed when only pulmonary vascular imaging was available to rule out pulmonary embolism. The intervention protocol used pretest probability assessment, a whole-blood d -dimer assay, and an alveolar dead-space measurement to rule out pulmonary embolism. The main outcomes were diagnosis of venous thromboembolism or sudden unexpected death within 90 days.

RESULTS

During baseline, 453 of 61,322 patients (0.74%; 95% confidence interval [CI] 0.67% to 0.81%) underwent pulmonary vascular imaging, and 8% (95% CI 6% to 11%) of scan results were positive; 1.20% (95% CI 0.39% to 2.78%) of untreated discharged patients were anticoagulated for venous thromboembolism or died unexpectedly within 90 days. The median length of stay was 385 minutes. After intervention, 1,460 of 102,848 patients (1.42%; 95% CI 1.35% to 1.49%) were evaluated for pulmonary embolism. Seven hundred fifty-two patients had a negative protocol and 5 of 752 (0.66%; 95% CI 0.20% to 1.54%) had venous thromboembolism within 90 days, none with unexpected death. After intervention, the rate of pulmonary vascular imaging tended to decrease (0.64%; 95% CI 0.59% to 0.69%), and more scans (11%; 95% CI 9% to 14%) were read as positive; the length of stay decreased to 297 minutes.

CONCLUSION

A point-of-care pulmonary embolism rule-out protocol doubled the rate of screening for pulmonary embolism in the ED, had a false negative rate of less than 1.0%, did not increase the pulmonary vascular imaging rate, and decreased length of stay.

CT venography in suspected pulmonary thromboembolism

Pulmonary embolism (PE) and deep venous thrombosis (DVT) are a continuum and are difficult to diagnose clinically. Combined CT venography and pulmonary angiography (CTVPA) is a single examination that combines multidetector CT pulmonary angiography (CTPA) and CT venography (CTV) of the abdomen, pelvis, and lower extremities, providing "one-stop shopping" for venous thromboembolism without additional venipuncture or i.v. contrast, and it adds only a few additional minutes to scanning time. CTVPA rapidly and accurately examines the deep veins, reveals the presence, absence, and extent of deep venous thrombosis, serves as a baseline, and helps guide patient management. Multiple investigators have reported a high degree of accuracy when CTV is compared with venous ultrasound. There are some pitfalls in image interpretation, especially with regard to mixing artifacts, and there are continuing controversies as to exactly which parts of the abdomen, pelvis, and legs should be scanned routinely, the ideal timing of CTV acquisition relative to contrast injection, and the slice thickness and gap, if any, that should be used.