In recent years, CTA has become the most common imaging modality for diagnosis of PE Compared to V/Q scanning, it is more rapid, more readily available, and can better characterize nonvascular structures Most studies have shown CTA to be ≥90% sensitive and specific for the diagnosis of PE, particularly in low- and intermediate-risk groups CTA is likely less sensitive for peripheral subsegmental emboli beyond main, lobar, or segmental pulmonary arteries Therefore, using current technology, a negative CTA cannot definitively rule out PE, especially in any patient considered to be at high risk Utilizing available data from history and physical examination, as well as adjunctive testing modalities described above forms the basis for decision making regarding management of patients with suspected PE Adults deemed to rule out for PE by PERC criteria, or who have low pretest probability by Wells or Geneva scores and a negative D-dimer are felt to have a low likelihood of PE and therefore may not need further evaluation with radiologic studies This may exempt one-third of presenting adult patients from requiring additional workup, and has been shown to have a negative predictive value of 99% D-dimer is of limited utility in excluding PE among patients considered to have high pretest probability of PE Therefore, patients with high pretest probability or an abnormal D-dimer being evaluated for PE should always have additional imaging performed Although many evaluation plans exist, the simplest has suggested that in such patients, a negative CTA was found to have an observed risk of missed diagnosis nearly identical to that identified by pulmonary arteriography TABLE 99.8 TREATMENT FOR FIRST-TIME DVT/PE IN CHILDREN There are a number of differences in children and adults that may make a similar approach to the evaluation for children with concern for PE less