Suspected Pulmonary Embolism

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Revised 2016

American College of Radiology

ACR Appropriateness Criteria®

Suspected Pulmonary Embolism

 

Variant 1:                         Suspected pulmonary embolism. Intermediate probability with a negative D-dimer or low pretest probability.

 

Radiologic Procedure Rating Comments RRL*
X-ray chest 9
This procedure should be optimized for
pulmonary arterial enhancement. This
CTA chest with IV contrast 5 procedure may be appropriate but there ☢☢☢
was disagreement among panel members
on the appropriateness rating as defined by
the panel’s median rating.
CT chest with IV contrast 3 This procedure should be optimized for ☢☢☢
pulmonary arterial enhancement.
US duplex Doppler lower extremity 3 This procedure has a low yield in the O
absence of symptoms of DVT.
CT chest without IV contrast 2 ☢☢☢
Tc-99m V/Q scan lung 2 ☢☢☢
CTA chest with IV contrast with CT 2 ☢☢☢
venography lower extremities
MRA chest without and with IV contrast 2 O
US echocardiography transthoracic resting 2 O
CT chest without and with IV contrast 1 ☢☢☢
Arteriography pulmonary with right heart 1 ☢☢☢☢
catheterization
MRA chest without IV contrast 1 O
US echocardiography transesophageal 1 O
Rating Scale: 1,2,3 Usually not appropriate; 4,5,6 May be appropriate; 7,8,9 Usually appropriate *Relative
Radiation Level

 

Variant 2: Suspected pulmonary embolism. Intermediate probability with a positive D-dimer or high
pretest probability.
Radiologic Procedure Rating Comments RRL*
X-ray chest 9
CTA chest with IV contrast 9 This procedure should be optimized for ☢☢☢
pulmonary circulation.
This procedure should be optimized for
CT chest with IV contrast 9 pulmonary circulation. This procedure ☢☢☢
may be an alternative to CTA, but both
should not be performed.
Tc-99m V/Q scan lung 7 This procedure may be an alternative to ☢☢☢
CTA, but both should not be performed.
US duplex Doppler lower extremity 7 This procedure may be an initial study O
prior to CTA.
MRA chest without and with IV contrast 6 O
CTA chest with IV contrast with CT 5 ☢☢☢
venography lower extremities
Arteriography pulmonary with right heart 3 ☢☢☢☢
catheterization
US echocardiography transthoracic resting 3 O
CT chest without IV contrast 2 ☢☢☢
CT chest without and with IV contrast 2 ☢☢☢
This procedure has limited sensitivity and
MRA chest without IV contrast 2 may be indicated for rare situations or O
certain contraindications for a specific
patient.
US echocardiography transesophageal 2 O
Rating Scale: 1,2,3 Usually not appropriate; 4,5,6 May be appropriate; 7,8,9 Usually appropriate *Relative
Radiation Level

 

Variant 3: Suspected pulmonary embolism. Pregnant patient.
Radiologic Procedure Rating Comments RRL*
X-ray chest 9
This procedure may be an initial
US duplex Doppler lower extremity 8 examination prior to CTA, which may O
prevent the need for ionizing radiation in
the appropriate clinical setting.
CTA chest with IV contrast 7 This procedure should be optimized for ☢☢☢
pulmonary circulation.
This procedure should be optimized for
CT chest with IV contrast 7 pulmonary circulation. This procedure ☢☢☢
may be an alternative to CTA, but both
should not be performed.
This procedure may be an alternative to
Tc-99m V/Q scan lung 7 CTA, but both should not be performed. ☢☢☢
Ventilation should be done only if
necessary.
Arteriography pulmonary with right heart This procedure is rarely indicated. It is ☢☢☢☢
4 used for clarification or catheter-directed
catheterization
intervention.
CTA chest with IV contrast with CT 3 ☢☢☢
venography lower extremities
This procedure may be used as a problem
MRA chest without and with IV contrast 3 solver or if intervention is planned. There O
is concern for fetal exposure to contrast.
MRA chest without IV contrast 3 O
CT chest without IV contrast 2 ☢☢☢
CT chest without and with IV contrast 2 ☢☢☢
US echocardiography transesophageal 2 O
US echocardiography transthoracic resting 2 O
Rating Scale: 1,2,3 Usually not appropriate; 4,5,6 May be appropriate; 7,8,9 Usually appropriate *Relative
Radiation Level

 

SUSPECTED PULMONARY EMBOLISM

 

Expert Panels on Cardiac and Thoracic Imaging: Jacobo Kirsch, MD 1 ; Richard K. J. Brown, MD2; Travis S. Henry, MD3; Cylen Javidan-Nejad, MD4; Clinton Jokerst, MD5 ; Paul R. Julsrud, MD6; Jeffrey P. Kanne, MD7; Christopher M. Kramer, MD8; Jonathon A. Leipsic, MD9; Kalpesh K. Panchal, MD10; James G. Ravenel, MD11; Amar B. Shah, MD12; Tan-Lucien H. Mohammed, MD13; Pamela K. Woodard, MD14; Suhny Abbara, MD.15

 

Summary of Literature Review

 

Introduction/Background

 

Over 290,000 cases of fatal pulmonary thromboembolism (PE) and 230,000 cases of nonfatal PE are estimated to occur in the United States each year [1]. Additional cases may not be diagnosed because symptoms such as chest pain, shortness of breath, and tachycardia are nonspecific and may mimic other pulmonary or cardiac conditions. Unsuspected PE continues to be a frequent autopsy finding.

 

It has been further estimated that over 80% of PE cases are associated with deep vein thrombosis (DVT). It is, therefore, easy to see why PE, for purposes of diagnosis and treatment, is often considered a complication or a consequence of DVT [2]. A concern with this approach is that some cases of PE are due to embolization from other sites, such as pelvic or upper-extremity veins or the right heart.

 

Diagnostic efforts in radiology are aimed at 1) reaching an acceptable level of diagnostic certainty of PE to warrant anticoagulant therapy, using the least-invasive tests, and 2) excluding other reasons for the patient’s symptoms. Historically, the probability of a patient having PE is arrived at using a Bayesian approach in which the pretest likelihood of the condition (PE), based on clinical and laboratory evidence, is modified by the results of the appropriate radiological procedure(s) in order to estimate a post- test probability of the condition. This approach has evolved over the last decade. Clinical decision trees, most notably the Wells criteria, have been developed and validated. There have also been major technological advances, primarily in computed tomography (CT) and magnetic resonance imaging (MRI). Many clinical studies have evaluated these modalities and the use of imaging in conjunction with clinical criteria and serum assay for D-dimer. High-sensitivity D-dimer testing using an enzyme-linked immunosorbent assay has improved the specificity of the diagnosis of PE. D-dimer levels will be elevated with any significant thrombotic process, so this test is of limited value in pregnant, postoperative, and trauma patients. It is also of limited value in patients determined to be at high risk of PE by validated clinical criteria. In all other settings, a negative D-dimer test effectively excludes PE or DVT [3-7].

 

Overview of Imaging Modalities

 

Chest Radiography

 

The posterior anterior and lateral chest radiograph is an important initial study in the evaluation of suspected PE. The chest radiograph may eliminate the need for additional radiographic procedures by revealing an alternate reason for acute symptoms, such as pneumonia or a large effusion [8]. A normal chest radiograph does not exclude PE, and there are no specific findings that are sufficient to confirm PE. A recent chest radiograph is required to allow accurate interpretation of an abnormal radionuclide ventilation/perfusion (V/Q) lung scan [9].

 

Computed Tomography

 

Multidetector CT pulmonary angiography (CTPA) is indicated in the evaluation of patients suspected of having a PE. CTPA is now the primary imaging modality for evaluating patients suspected of having acute PE. CTPA has played an increasingly significant role in the diagnosis of PE since the first major clinical study in 1992 by Remy-Jardin et al [10]. Technological advancements in CT—from helical to multidetector—have led to improved resolution of the pulmonary arteries, large and small. Numerous studies have examined the accuracy of CTPA compared to V/Q imaging and conventional angiography [11-19]. Although conventional CT with contrast material (not performed as dedicated CTPA) is generally not indicated in the routine workup of acute chest pain thought to be secondary to acute PE, it should be acknowledged that incidental PE can be accurately diagnosed on routine chest CT with contrast [20,21].

 

It is important to recognize that the increased sensitivity of CT has raised concerns related to evidence of substantial increase in complications from anticoagulation due to the overdiagnosis of PE. However, studies are needed to better determine which small emboli may benefit from treatment and which can go untreated [22,23].

 

For the purposes of distinguishing between CT and CT angiography (CTA), American College of Radiology (ACR) Appropriateness Criteria topics use the definition in the Practice Parameter for the Performance and Interpretation of Body Computed Tomography Angiography (CTA) [24]:

 

“CTA uses a thin-section CT acquisition that is timed to coincide with peak arterial or venous enhancement. The resultant volumetric dataset is interpreted using primary transverse reconstructions as well as multiplanar reformations and 3D renderings.”

 

All elements are essential: 1) timing, 2) reconstructions/reformats, and 3) 3-D renderings. Standard CTs with contrast also include timing issues and recons/reformats. Only in CTA, however, is 3-D rendering a required element. This corresponds to the definitions that the Centers for Medicare & Medicaid Services has applied to the Current Procedural Terminology codes.

 

Ventilation and Perfusion Imaging

 

Since its introduction in the mid-1960s, lung perfusion imaging has been indicated in the workup of patients with suspected PE [8,9]. The role of lung perfusion imaging for evaluating suspected PE has considerably diminished with the widespread use of CTPA. Still, a normal pattern of regional perfusion in multiple projections, accompanied by a normal ventilation scan, is widely accepted as indicating that pulmonary emboli are not present and no further workup for PE is necessary.

 

An abnormal pattern of regional lung perfusion may suggest the diagnosis of PE, but it is not specific. It requires evaluation of the anatomic basis of the perfusion defect (ie, segmental or not) as well as correlation with other modalities such as ventilation imaging and a recent chest radiograph [25,26]. These studies are performed to differentiate between reduced pulmonary arterial blood flow due to vascular obstruction and secondary reductions in regional blood flow associated with a variety of airway diseases [25-36].

 

A number of schemes based on various V/Q scan patterns have been developed to assign different probabilities for the presence (or absence) of PE [26,27,29,30,35,36]. Generally, V/Q findings are categorized as “high probability,” “intermediate probability” (not meeting the criterion of either “high” or “low”), “low probability,” “very low probability,” and “normal.” All the probability schemes incorporate the results of a recent chest radiograph. At least 1 study suggests that using single-photon emission CT (SPECT) imaging improves the sensitivity and specificity of V/Q scintigraphy [34].

 

Ventilation imaging can be performed before or after Tc-99m macroaggregated albumin (MAA) perfusion imaging. Performing a low-dose MAA perfusion scan before the Xe-133 ventilation scan allows the ventilation scan to be obtained in the appropriate projection, rather than the usual posterior projection. In addition, a normal perfusion scan can obviate the need to perform the ventilation scan, thus lowering radiation dose to the patient. Results with Tc-99m-labeled microaerosol agents (diethylenetriamine pentaacetic acid, pertechnetate, etc) are comparable to those of studies using inert gases such as xenon or krypton and have the advantage of providing multiple views for regional V/Q comparisons.

 

Macroaggregated Albumin Perfusion Imaging Without Ventilation Imaging

 

MAA perfusion imaging without ventilation may be indicated, particularly when the condition of the patient suddenly deteriorates and acute PE is suspected as a significant contributing cause. A demonstration of regions of reduced perfusion, not explained by recent chest radiograph findings, warrants a consideration of PE and possibly the need for further workup such as pulmonary angiography. It may also be indicated in patients who are not candidates for multidetector CTA, such as those who are too large to fit into CT gantries, who are unable to remain still and hold their breath for the few seconds necessary, or who have severe renal impairment.

 

Catheter-Directed Selective Pulmonary Angiography

 

Pulmonary angiography, including right heart catheterization and measurement of pulmonary artery and right heart pressures, is an acceptably safe, albeit invasive, procedure when performed by an experienced operator with adequate patient monitoring. The results may establish the specific diagnosis of PE when an acceptable level of certainty cannot be reached by noninvasive imaging [27,28,33]. Given the accuracy of CTPA, however, unacceptably low levels of certainty are increasingly rare. Further, the experience of the radiologist who performs and interprets this invasive procedure is crucial. As indicated, studies suggest that the overall accuracy of catheter pulmonary angiography may be inferior to that of multidetector CTPA due to technical factors such as patient movement and vessel overlap, as well as inter- and intraobserver variability in interpretation.

 

The amount of contrast material injected should be limited to that necessary to establish (or exclude) the presence of PE. The number of selective arterial injections can be reduced by focusing on suspicious pulmonary vascular territories indicated by the results of noninvasive V/Q lung scanning. Magnification techniques and imaging in special projections may overcome problems with overlapping vessels.

 

Ultrasound

 

Transthoracic echocardiogram and transesophageal echocardiogram studies are generally not indicated in the diagnosis of acute PE in the setting of acute chest pain [32]. However, these ultrasound (US) procedures are useful in evaluating right ventricular morphology and function that in turn have prognostic implications for morbidity, mortality, and development of future venous thromboembolism [31,37-41].

 

Magnetic Resonance Angiography, Magnetic Resonance Imaging, and Perfusion Imaging

 

Magnetic resonance angiography (MRA) and MR perfusion imaging can provide rapid, noninvasive evaluation of the central and segmental pulmonary arteries [42-45]. Current MRI technology demonstrates high specificity and high sensitivity for proximal PE but still limited sensitivity for distal PE and 30% of inconclusive results [46]. The PIOPED III (Prospective Investigation of Pulmonary Embolism Diagnosis III) Trial was a multicenter study designed to assess the sensitivity and specificity of MRA, alone or with magnetic resonance venography, for diagnosing PE and venous thromboembolism. It showed that technically adequate MRA had a sensitivity of 78% and a specificity of 99% and that technically adequate MRA and venography had a sensitivity of 92% and a specificity of 96%. It is important to note that the study had a high number of technically inadequate results (up to 52% of patients in the MRA and venography group) and that this varied significantly by clinical center. Due to these findings, the investigators recommended MRA to be considered only at centers that routinely perform it well and only for patients for whom standard tests are contraindicated [47,48]. A recent study from Schiebler et al

  • demonstrated that pulmonary MRA studies reach a negative predictive value of up to 97% in patients when followed up clinically for evidence of venous thromboembolism. Just as important, they report 95% of their studies to be of diagnostic quality.

 

MR perfusion imaging has high sensitivity for PE and is most useful when combined with MRI and MRA [42].

 

MRI without MRA is probably not indicated in the routine evaluation of patients with suspected PE. It may rarely be useful in patients who have large central emboli, particularly if used in conjunction with MRI for other indications, such as cardiac morphologic evaluation [50,51].

 

Discussion of the Imaging Modalities by Variant

 

Variant 1: Suspected pulmonary embolism. Intermediate probability with a negative D-dimer or low pretest probability.

In hemodynamically stable patients with a low or intermediate clinical probability of PE, normal results on D-dimer testing avoid unnecessary further investigation. In such patients, if anticoagulant treatment is not given, the estimated 3-month risk of thromboembolism is 0.14% (95% confidence interval, 0.05–0.41) [3].

 

In 2011, the National Quality Forum (NQF) endorsed an imaging efficiency measure directed at the appropriateness of CTPA use in emergency department patients. According to NQF measures, imaging was avoidable in 32% of patients, with failure to perform D -dimer testing responsible for nearly two-thirds of potentially avoidable imaging studies [52]. A meta-analysis of 52 studies, comprising 55,268 patients, comparing the test characteristics of gestalt (a physician’s unstructured estimate) and clinical decision rules for evaluating adults with suspected PE showed that PE can be safely excluded by a low clinical probability assessment and a negative D-dimer result without the need of imaging [53].

 

The PIOPED investigators reported that the combination of a low -probability V/Q scan result and low clinical suspicion reduced the likelihood of PE to <5%. This observation suggests that excluding PE in patients with minimal scan abnormalities and low clinical suspicion for this disorder may be reasonable [54].

 

The intermediate pretest probability subgroup may present a more challenging diagnostic enigma. For these patients D-dimer testing is warranted [55]. Recent studies have demonstrated that a normal high-sensitivity D-dimer level can be used to further risk- stratify patients at both low and intermediate risk for PE. Perrier et al [56] enrolled 674 non–high-risk patients (at either low or intermediate risk for PE). Those with normal D-dimer levels were followed for 3 months and no thromboembolic events were noted [55,56]. Warren et al [57] used the Wells criteria, and Gupta et al [6] used the revised Geneva score. They evaluated 1679 and 330 patients, respectively, who were determined to be at intermediate risk for PE and found that a normal D-dimer level was 99.5% and 100% sensitive, respectively for excluding PE on CT [6,55,57]. A negative result from a high-sensitivity D-dimer test in patients with either low or intermediate probability safely excludes PE without the need for further imaging.

 

Variant 2: Suspected pulmonary embolism. Intermediate probability with a positive D-dimer or high pretest probability.

 

Multiple studies have shown that CTPA is highly sensitive and specific [12,17,18,58,59]; discrepancies with conventional angiography are mainly at the subsegmental level where even angiographers tend to have poor interobserver agreement. Intraobserver and interobserver variability for CTPA have been shown to be very good to the segmental level, better than with V/Q imaging.

 

The overall accuracy of CTPA appears to be very high and is even higher when combined with clinical assessment and serum D- dimer testing. A positive CTPA result combined with high or intermediate suspicion on clinical assessment has a high positive predictive value. In addition, the adjunctive use of CT venography with CTPA improves the sensitivity of detecting DVT, with similar specificity, thereby increasing the overall accuracy of the diagnosis of thromboembolic disease, as compared to an isolated diagnosis of PE [20,58,59].

 

CTPA also has fewer “nondiagnostic” studies than V/Q scans. The false-negative rate of CTPA is very low. Outcome studies have shown no adverse outcomes in patients with a negative CTPA who were not subsequently treated. Another study has shown CTPA to be cost effective in conjunction with lower-extremity duplex examinations. The combination of multidetector CTPA and high-specificity D-dimer testing has very high positive and negative predictive values [12,20,60]. In addition, CTPA may occasionally demonstrate pathology other than PE that may be responsible for the patient’s symptoms.

 

CTPA can also identify signs of right ventricular dysfunction that may have prognostic significance or implications for treatment (eg, need for the institution of thrombolytic therapy versus conventional anticoagulation alone). Measurements of right ventricular enlargement and reflux of contrast to the inferior vena cava have been used among other indexes to gauge right ventricular dysfunction and predict patient mortality [61-65]. Recent technological advancements such as electrocardiogram- gated CT and dual-source CT have allowed accurate evaluation of the pulmonary vasculature, thoracic aorta, and coronary arteries on a single CT study. This so-called triple rule-out CT protocol has been shown to be feasible, although it has yet to be proven useful or cost effective through large-scale clinical trials [66-68].

 

In general, the data indicate that multidetector CTPA is more sensitive than single-slice CT or other studies, such as V/Q scans. Studies have shown that the high resolution of CTPA makes it possible to detect filling defects in distal subsegmental arteries as small as 2–3 mm in diameter [69]. Only 1% of V/Q scans rated as “high probability” correspond to an isolated subsegmental PE [70], compared with 15% of positive CTPA scans [71]. However, these distal very small clots remain of indeterminate clinical significance and some of them may not require treatment [23].

 

The general indications for pulmonary catheter angiography in the past have included: a) cases with “low probability” or “intermediate probability” V/Q scan findings, particularly when there is a high clinical suspicion for PE, and anticoagulation is considered risky or relatively contraindicated; b) when pulmonary thromboendarterectomy or thrombolysis is considered (eg, chronic pulmonary hypertension secondary to major vessel thromboembolic occlusion or symptomatic massive or submassive PE that may require catheter-directed therapy); and c) before placement of an inferior vena cava filter. Because multidetector CTPA is currently the standard of care for PE detection, there are now far fewer cases in which catheter pulmonary angiography is indicated or necessary, and these are now largely confined to situations in which catheter-directed thrombectomy or thrombolysis is thought to be clinically indicated.

 

Because of the high association of DVT with PE, US evaluation of the venous drainage of the lower extremities may be indicated, especially in patients with signs and symptoms of DVT. US studies include duplex Doppler with leg compression and continuous-wave Doppler [72,73]. The presence of DVT does not indicate the presence of PE but increases its likelihood. Also, positive DVT studies may identify patients at higher risk for subsequent PE. In most patients, however, the presence of DVT—whether or not associated with PE—has identical treatment, so no further diagnostic evaluation for PE is needed. A negative extremity US study does not exclude PE, although it significantly decreases its likelihood [74-76]. For a more detailed discussion on DVT, refer to the ACR Appropriateness Criteria®Suspected Lower Extremity Deep Vein Thrombosis” [77].

 

Variant 3: Suspected pulmonary embolism. Pregnant patient.

 

PE is a leading cause of pregnancy-related mortality in the developed world, accounting for 20% of maternal deaths in the United States [78]. The American Thoracic Society/Society of Thoracic Radiology (ATS/STR) Committee on Pulmonary Embolism in Pregnancy published their Clinical Practice Guideline—Evaluation of Suspected Pulmonary Embolism in Pregnancy, summarized in 7 recommendations that put a high value on avoiding workup with radiation-associated tests if possible [78]. Lower- extremity duplex ultrasonography for assessment of DVT was recommended in pregnant patients with suspected PE and signs and symptoms of lower-extremity DVT as a means of determining the presence of thrombosis suggestive of pulmonary thromboembolism without radiation [78].

 

The modality of choice (CTPA versus V/Q scan) in pregnant patients remains a matter of debate [79,80]. Fetal radiation doses delivered in utero by properly performed diagnostic tests present no measurably increased risk of prenatal death, malformation, or impairment of mental development over the background incidence of these entities. The ATS/STR statement recommends scintigraphy over CTA mainly over maternal, not fetal, radiation dose concerns [78].

 

When lung scans are indicated in pregnant women, the administered dose of the radiopharmaceutical(s) should be reduced by a factor of 2 or more, with correspondingly longer acquisition times to achieve adequate imaging statistics. Doing so may minimize absorbed radiation dose. If the MAA perfusion scan is performed first and is normal, the ventilation scan can be avoided.

 

A follow-up MAA perfusion scan may be recommended 6–8 weeks after the discovery of a “mismatched” V/Q pattern (presumption of PE). Failure of observed resolution, or of at least significant improvement in regional perfusion, may signal the development of pulmonary hypertension secondary to chronic thromboembolic obstruction in the major pulmonary vessels. This complication has an expected incidence of <1%. Caution should be exercised in interpreting perfusion imaging in the days after acute PE because reestablishment of regional perfusion (resolution of defects) occurs at varying and unpredictable rates. Conversely, local ventilation may be compromised for minutes to hours after an acute PE.

 

The use of pulmonary MR pulmonary angiography is also of at least theoretical value in pregnant patients, as well as patients in whom the use of iodinated contrast agents is contraindicated [81]. Although there are no studies to date suggesting that there is risk to a developing fetus, there is also no proof that the use of gadolinium-containing contrast agents is safe. They should, therefore, be used only when clearly indicated.

 

Summary of Recommendations

 

Variant 1

 

  • In patients with low or intermediate clinical probability of PE, normal results on D-dimer testing avoid unnecessary further investigation.

 

Variant 2

 

  • CTPA is highly sensitive and specific.
  • CTPA also has fewer “nondiagnostic” studies than V/Q scans.
  • There is a high association of DVT with PE; therefore, US evaluation of the venous drainage of the lower extremities may be indicated, especially in patients with signs and symptoms of DVT.

 

Variant 3

 

  • Workup with radiation-associated tests should be avoided if possible.
  • Lower-extremity duplex ultrasonography for assessment of DVT is recommended in pregnant patients with suspected PE and signs and symptoms of lower-extremity DVT.
  • There is still some debate over the preference of CTPA or scintigraphy.

 

Summary of Evidence

 

Of the 86 references cited in the ACR Appropriateness Criteria® Suspected Pulmonary Embolism document, all of them are categorized as diagnostic references including 11 well-designed studies, 15 good- quality studies, and 27 quality studies that may have design limitations. There are 31 references that may not be useful as primary evidence. There are 2 references that are meta-analysis studies.

 

The 86 references cited in the ACR Appropriateness Criteria® Suspected Pulmonary Embolism document were published from 1979-2015.

 

While there are references that report on studies with design limitations, 26 well-designed or good-quality studies provide good evidence.

 

Safety Considerations in Pregnant Patients

 

Imaging of the pregnant patient can be challenging, particularly with respect to minimizing radiation exposure and risk. For further information and guidance, see the following ACR documents:

 

ACR-SPR Practice Parameter for Imaging Pregnant or Potentially Pregnant Adolescents and Women with Ionizing Radiation [82]

 

ACR-ACOG-AIUM-SRU Practice Parameter for the Performance of Obstetrical Ultrasound [83] ACR Guidance Document on MR Safe Practices [84]

 

ACR Manual on Contrast Media [85]

 

Anticipated Exceptions

 

If multidetector CTPA is not available, then V/Q scans, pulmonary MRA, and/or lower-extremity US may need to be used for evaluation. The choice between CTPA and V/Q scanning in pregnant patients remains unresolved. With careful, modern techniques, both are acceptable. The radiation dose to the fetus, in general, is probably lower with V/Q scanning, although dose-modulation techniques with CT may make the 2 modalities nearly equivalent in absorbed dose. If a chest radiograph is abnormal, CTPA has a higher likelihood of being definitive [86].

 

Relative Radiation Level Information

 

Potential adverse health effects associated with radiation exposure are an important factor to consider when selecting the appropriate imaging procedure. Because there is a wide range of radiation exposures associated with different diagnostic procedures, a relative radiation level (RRL) indication has been included for each imaging examination. The RRLs are based on effective dose, which is a radiation dose quantity that is used to estimate population total radiation risk associated with an imaging procedure. Patients in the pediatric age group are at inherently higher risk from exposure, both because of organ sensitivity and longer life expectancy (relevant to the long latency that appears to accompany radiation exposure). For these reasons, the RRL dose estimate ranges for pediatric examinations are lower as compared to those specified for adults (see Table below). Additional information regarding radiation dose assessment for imaging examinations can be found in the ACR Appropriateness Criteria® Radiation Dose Assessment Introduction document.

 

Relative Radiation Level Designations

 

Relative Radiation Level* Adult Effective Dose Estimate Pediatric Effective Dose Estimate
Range Range
O 0 mSv 0 mSv
<0.1 mSv <0.03 mSv
☢☢ 0.1-1 mSv 0.03-0.3 mSv
☢☢☢ 1-10 mSv 0.3-3 mSv
☢☢☢☢ 10-30 mSv 3-10 mSv
☢☢☢☢☢ 30-100 mSv 10-30 mSv

 

*RRL assignments for some of the examinations cannot be made, because the actual patient doses in these procedures vary as a function of a number of factors (eg, region of the body exposed to ionizing radiation, the imaging guidance that is used). The RRLs for these examinations are designated as “Varies”.

 

Supporting Documents

 

For additional information on the Appropriateness Criteria methodology and other supporting documents go to www.acr.org/ac.

 

References

 

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The ACR Committee on Appropriateness Criteria and its expert panels have developed criteria for determining appropriate imaging examinations for diagnosis and treatment of specified medical condition(s). These criteria are intended to guide radiologists, radiation oncologists and referring physicians in making decisions regarding radiologic imaging and treatment. Generally, the complexity and severity of a patient’s clinical condition should dictate the selection of appropriate imaging procedures or treatments. Only those examinations generally used for evaluation of the patient’s condition are ranked. Other imaging studies necessary to evaluate other co-existent diseases or other medical consequences of this condition are not considered in this document. The availability of equipment or personnel may influence the selection of appropriate imaging procedures or treatments. Imaging techniques classified as investigational by the FDA have not been considered in developing these criteria; however, study of new equipment and applications should be encouraged. The ultimate decision regarding the appropriateness of any specific radiologic examination or treatment must be made by the referring physician and radiologist in light of all the circumstances presented in an individual examination.

1Principal Author, Cleveland Clinic, Weston, Florida. 2University Hospital, Ann Arbor, Michigan. 3University of California San Francisco, San Francisco, California. 4Mallinckrodt Institute of Radiology, Washington University School of Medicine, Saint Louis, Missouri. 5 Banner University Medical Center, Tucson, Arizona. 6Mayo Clinic, Rochester, Minnesota. 7University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin. 8University of Virginia Health System, Charlottesville, Virginia, American College of Cardiology. 9St. Paul’s Hospital, Vancouver, British Columbia, Canada. 10University of Cincinnati Hospital, Cincinnati, Ohio. 11Medical University of South Carolina, Charleston, South Carolina. 12Westchester Medical Center, Valhalla, New York. 13Specialty Chair, University of Florida College of Medicine, Gainesville, Florida. 14Specialty Chair, Mallinckrodt Institute of Radiology, Washington University School of Medicine, Saint Louis, Missouri. 15Panel Chair, UT Southwestern Medical Center, Dallas, Texas.

The American College of Radiology seeks and encourages collaboration with other organizations on the development of the ACR Appropriateness Criteria through society representation on expert panels. Participation by representatives from collaborating societies on the expert panel does not necessarily imply individual or society endorsement of the final document.

Reprint requests to: publications@acr.org