Lower Voltage CT Angiography Effective Even with Higher BMI

Despite an increased body mass, radiologists could still accurately read computed tomography pulmonary angiography (CTPA) results at the lower 100 kVp tube voltage in patients weighing up to 125 kg, according to the results of a study published recently in Clinical Radiology. 

According to the study, industry standard for CTPA is slowly moving towards the use of 100 kVp tube voltage in place of the former protocols of 120 to 140 kVp.

“The most important reason to use a lower peak tube voltage for CT angiography is to reduce the radiation dose to the patient,” wrote Boglarka Megyeri of the University of Debrecen, and colleagues. “Although low voltage CT angiography is feasible in virtually all body regions, it is especially attractive for the chest, as the image noise increases less steeply at lower tube voltage in this body region than in the abdomen because of the low X-ray absorption of the air-filled lungs.”

The researchers conducted a retrospective study of 216 patients with body weights ranging from 75 kg to 150 kg. Almost 60% of the patient population was obese. Patients received CTPA at 100 kVp to exclude a diagnosis of pulmonary embolism. The study measured size-specific dose estimates as well as contrast-to-noise ratio. Three radiologists reviewed the images for quality and diagnostic confidence.

Results showed that vessel attenuation in the main pulmonary artery was significantly higher for patients weighing 75 to 99 kg compared with all other weight groups. However, once patients reached a body weight greater than 100 kg, there was no difference in vessel attenuation between groups. In addition, contrast-to-noise ratio was significantly higher in patients in the 75 to 99 kg body weight group (P<.0006).

The researchers found that the size-specific dose estimates were significantly lower in patients weighing 75 to 99 kg compared with patients in the higher body weight groups. However, again, no difference in size-specific dose estimate was found between patients weighing 100 to 125 kg and those weighing 125 to 150 kg.

“Objective image quality parameters such as vessel attenuation and contrast-to-noise ratio were dependent on patient body weight but not on body mass index,” the researchers wrote. “In contrast, subjective quality rating and diagnostic confidence were influenced neither by body mass index nor by body weight.”

Megyeri and colleagues concluded that the 100 KvP tube voltage could be accurately used in patients weighing up to 125 kg, but that more study should be done of image quality and diagnostic confidence in patients weighing 125 to 150 kg.