Imaging of suspected pulmonary embolism and deep venous thrombosis in obese patients

Abstract

Obesity is a growing problem around the world, and radiology departments frequently encounter difficulties related to large patient size. Diagnosis and management of suspected venous thromboembolism, in particular deep venous thrombosis (DVT) and pulmonary embolism (PE), are challenging even in some lean patients, and can become even more complicated in the setting of obesity. Many obstacles must be overcome to obtain imaging examinations in obese patients with suspected PE and/or DVT, and to ensure that these examinations are of sufficient quality to diagnose or exclude thromboembolic disease, or to establish an alternative diagnosis. Equipment limitations and technical issues both need to be acknowledged and addressed. Table weight limits and scanner sizes that readily accommodate obese and even morbidly obese patients are not in place at many clinical sites. There are also issues with image quality, which can be substantially compromised. We discuss current understanding of the effects of patient size on imaging in general and, more specifically, on the imaging modalities used for the diagnosis and treatment of DVT and PE. Emphasis will be placed on the technical parameters and protocol nuances, including contrast dosing, which are necessary to refine and optimize images for the diagnosis of DVT and PE in obese patients, while remaining cognizant of radiation exposure. More research is necessary to develop consistent high-level evidence regarding protocols to guide radiologists, and to help them effectively utilize emerging technology.

Weight-Adjusted Contrast Administration in the Computed Tomography Evaluation of Pulmonary Embolism

“…This technique is suited to CTPA because of its short scan duration, usually within four to six seconds, depending on Z-axis coverage. Therefore, to compensate for obese patients, increasing contrast administration rate and higher concentrations of iodinated contrast media may help maintain diagnostic PA enhancement levels [33,34]. This study highlights the importance of tailoring imaging techniques to individual patients; implementation of protocol B using a weight-adjusted contrast dose demonstrated a significant increase in PA enhancement in this cohort from 264.1 HU (protocol A) to 312.9 HU (protocol B), an increase of 18.48% (P ¼ X).…”

Impact of Obesity in Critical Illness

“…69 Diagnosis of VTE on ultrasound in obesity may be challenging because increased subcutaneous tissue can make visualizing deeper proximal veins difficult. 70 Establishing venous compressibility with significant subcutaneous tissue may be difficult, potentially resulting in false-positive results. 70 Physicians should incorporate a careful physical examination and clinical impression into the interpretation of ultrasound results in critically ill patients with obesity and suspected VTE.…”

Canadian Society of Thoracic Radiology/Canadian Association of Radiologists Best Practice Guidance for Investigation of Acute Pulmonary Embolism, Part 2: Technical Issues and Interpretation Pitfalls

“…Slowing gantry rotation and lowering the pitch can also be helpful in reducing image noise, however these modifications come at a cost of increasing risk of motion artifact and increased radiation dose. 13 The use of iterative reconstruction in this patient population can be useful to improve image quality while minimizing radiation dose. 14…”

“…Although kVp can be increased as high as 140, multiple studies have shown that 120 kVp is adequate for most obese patients. 13 Increasing the mAs will also decrease noise, but at the cost of increasing radiation dose to the patient. The use of automatic tube current modulation software permits automatic adjustment of the tube current according to patient size and can help to optimize image quality without excess radiation exposure.…”

“…Slowing gantry rotation and lowering the pitch can also be helpful in reducing image noise, however these modifications come at a cost of increasing risk of motion artifact and increased radiation dose. 13…”