2017 ACR适宜性标准：疑似肺动脉高压

Abstract

Pulmonary hypertension may be idiopathic or related to a large variety of diseases. Various imaging examinations that may be helpful in diagnosing and determining the etiology of pulmonary hypertension are discussed. Imaging examinations that may aid in the diagnosis of pulmonary hypertension include chest radiography, ultrasound echocardiography, ventilation/ perfusion scans, CT, MRI, right heart catheterization, pulmonary angiography, and fl uorine-18-2- fl uoro-2-deoxy- D -glucose PET/CT.

The American College of Radiology Appropriateness Criteria are evidence-based guidelines for speci fi c clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision include an extensive analysis of current medical literature from peer reviewed journals and the application of well-established methodologies (RAND/UCLA Appropriateness Method and Grading of Recommendations Assessment, Development, and Evaluation or GRADE) to rate the appropriateness of imaging and treatment procedures for speci fi c clinical scenarios. In those instances where evidence is lacking or equivocal, expert opinion may supplement the available evidence to recommend imaging or treatment.

Key Words: Appropriateness Criteria, Appropriate Use Criteria, AUC, idiopathic pulmonary arterial hypertension, imaging, pulmonary hypertension, suspected pulmonary hypertension

J Am Coll Radiol 2017;14:S350-S361. Copyright ' 2017 American College of Radiology

a Principal Author, University of Arizona, Tucson, Arizona. b Panel Vice-Chair, Vanderbilt University Medical Center, Nashville, Tennessee. c Southern Illinois University School of Medicine, Spring fi eld, Illinois; Society of Thoracic Surgeons. d University of California, San Francisco, San Francisco, California. e University of Iowa, Iowa City, Iowa; Society of Thoracic Surgeons. f Mayo Clinic, Rochester, Minnesota. g University of Michigan Medical Center, Ann Arbor, Michigan. h Vanderbilt University Medical Center, Nashville, Tennessee; American College of Chest Physicians. i Radiology Imaging Associates, Englewood, Colorado. j University of Texas MD Anderson Cancer Center, Houston, Texas. k Specialty Chair, University of Florida College of Medicine, Gainesville, Florida. l Panel Chair, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin. Corresponding author: Arlene Sirajuddin, MD, Attn: Dept of Radiology, 1501 N Campbell Avenue, Tucson, AZ 85724; e-mail: asirajuddin2015@ gmail.com . 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 fi nal document. Reprint requests: publications@acr.org Dr. Kanne reports personal fees from HealthMyne, personal fees from Parexel Informatics, outside the submitted work. Dr. Travis S. Henry reports spouse is an employee of Genentech. The other authors have no con fl icts of interest related to the material discussed in this article.

Disclaimer: The ACR Committee on Appropriateness Criteria and its expert panels have developed criteria for determining appropriate imaging examinations for diagnosis and treatment of speci fi ed 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 in fl uence the selection of appropriate imaging procedures or treatments. Imaging techniques classi fi ed 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 speci fi c radiologic examination or treatment must be made by the referring physician and radiologist in light of all the circumstances presented in an individual examination.

ª 2017 American College of Radiology 1546-1440/17/\$36.00 n http://dx.doi.org/10.1016/j.jacr.2017.01.040

ACR Appropriateness Criteria Suspected Pulmonary Hypertension. Variant 1 and Table 1 .

Variant 1. Suspected pulmonary hypertension.

||Rating||RRL| |---|---|---|---| |US echocardiography transthoracic|| Catheterization and echocardiography are complementary examinations. Both should be performed. Echocardiography is typically performed before catheterization. || |Catheterization right heart|| Catheterization and echocardiography are complementary examinations. Both should be performed. Echocardiography is typically performed before catheterization. || |X-ray chest|| X-ray chest is usually performed during the initial workup/ screening of suspected pulmonary hypertension and is often the frst test performed. || |CTA chest with IV contrast|| This procedure is equivalent to CT chest with IV contrast. The examination choice of CTA chest with IV contrast or CT chest with IV contrast depends on institutional preference. This procedure is the examination of choice to evaluate for CTEPH. This procedure is equivalent to CTA chest with IV contrast. The || |Tc-99m V/Q scan lung|||| |CT chest with IV contrast|| This procedure is equivalent to CTA chest with IV contrast. The examination choice of CTA chest with IV contrast or CT chest with IV contrast depends on institutional preference. || | MRI heart function and morphology without IV contrast |||| | MRI heart function and morphology without and with IV contrast |||| |MRA chest without and with IV contrast|| CTA chest with IV contrast has better sensitivity for detection of CTEPH. || | US echocardiography transesophageal CT chest without IV contrast |||| ||| If there is a concern for an occult interstitial lung disease, HRCT may be appropriate. || | Arteriography pulmonary with right heart catheterization || Noninvasive imaging is generally performed instead. This procedure can be performed when considering surgical or percutaneous embolectomy. |8888| |MRA chest without IV contrast|||| |FDG-PET/CT heart|||8888| |CT chest without and with IV contrast|||888|

Note: Rat scale: 1, 2, ${\mathsf{Z}}={\mathsf{\Omega}}$ usually not appropriate; 4, 5, 6 ¼ may be propriate; 7, 8, ${\mathsf{9}}=$ usually appropriate. CTA ¼ CT angiography; CTEPH ¼ chronic thromboembolic pulmonar ertension; FDG-PET ¼ positron emission tomography using fl uorine-18-2- fl uoro-2-deoxy-Dglucose imaging; HRCT $=$ high-resolution CT; IV $\mathsf{I V}=$ ¼ intravenous; MRA $=$ MR angiography; RRL $=$ relative radiation level; US $=$ ultrasound; V/Q ¼ ventilation/perfusion.

Table 1. Relative radiation level designations

|RRL|Adult Effective Dose Estimate Range (mSv)|Pediatric Effective Dose Estimate Range (mSv)| |---|---|---| |||| ||K0.1|| ||0-1-1| Λ0.0W 0.03-0.3 | ||1-10|O.W-W| ||10-30|W-10| |88888|30-100|10-30|

Note: Relative radiation level (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. ”

## SUMMARY OF LITERATURE REVIEW

Introduction/Background

Pulmonary hypertension (PH), de fi ned by a mean pulmonary arterial pressure ' 25 mm Hg at rest (measured at right heart catheterization [RHC]), may be idiopathic or may be related to a large variety of diseases ( Variant 1 ). Normal mean pulmonary arterial pressure at rest is 14 to 20 mm Hg. Mean pulmonary arterial pressure between 21 and $24\;\mathrm{\mm}\;\mathrm{Hg}$ is of uncertain clinical signi fi cance but warrants close follow-up [1,2] . PH will lead to right ventricular failure and subsequent death if left untreated [1-4] .

The term pulmonary arterial hypertension (PAH) is used to describe a population of PH patients who have precapillary PH (pulmonary artery wedge pressure ${\leq}15\;\mathrm{mm\;Hg}$ and pulmonary vascular resistance ${>}3$ Wood units) in the absence of other causes of precapillary PH such as chronic thromboembolic PH (CTEPH) [2] .

A series of global meetings has been critical in the evolution of understanding PH, as well as in developing the clinical classi fi cation of PH. The fi rst World Symposium on Pulmonary Hypertension was held in 1973 in Geneva, Switzerland [5] . Since 1973, several world symposia on PH have taken place (Evian, France, in 1998; Venice, Italy, in 2003; Dana Point, California, in 2008), resulting in various updates to the clinical classi fi cation [6-8] . The clinical classi fi cation was most recently updated at the fi fth World Symposium on Pulmonary Hypertension, held in Nice, France, in 2013 [2,9] .

The 2013 updated clinical classi fi cation of PH includes Group 1, PAH; Group 1 0 , pulmonary venoocclusive disease (PVOD) and/or pulmonary capillary hemangiomatosis (PCH); Group $1^{\prime\prime}$ , persistent PH of the newborn; Group 2, PH due to left heart disease; Group 3, PH due to lung diseases and/or hypoxia; Group 4, CTEPH and other pulmonary artery obstructions; and Group 5, PH with unclear and/or multifactorial mechanisms [2] (see Appendix 1 ).

The signs and symptoms of PH are nonspeci fi c and may include fatigue, dyspnea, weakness, angina, peripheral edema, hepatomegaly, ascites, and syncope [10,11] . Because of the nonspeci fi c symptoms as well as the large, diverse group of diseases that can cause PH, diagnosis can be challenging. A careful history is critical to evaluate for risk factors for PH, including family history, history of drugs and toxins associated with PH, collagen vascular disease, human immunode fi ciency virus, portal hypertension, congenital or left heart

disease, and venous thromboembolic disease [11,12] . Clinical evaluation includes pulmonary function tests, arterial blood gases, routine biochemistry, hematology, thyroid function, and serological testing to evaluate for lung disease, liver disease, connective tissue disorders, and human immunode fi ciency virus [12] . Imaging examinations that may aid in the diagnosis of PH include chest radiography (CXR), ultrasound (US) echocardiography, ventilation/perfusion (V/Q) scans, CT, MRI, RHC, pulmonary angiography, and fl uorine-18-2- fl uoro-2-deoxy- D -glucose PET/CT (FDGPET/CT).

Overview of Imaging Modalities

CXR. CXR is often the fi rst imaging test performed because the clinical presentation of PH is nonspeci fi c. Multiple historic studies have demonstrated that CXR is an appropriate study in the initial evaluation of PH [13-19] . Additionally, Miniati et al [20] showed high sensitivity $(96.9\%)$ and speci fi city $(99.1\%)$ ) for detection of PH by CXR. However, CXR is known to be insensitive in the detection of mild PH. Thus, a normal CXR does not exclude PH and further imaging evaluation should be pursued if there are persistent unexplained symptoms such as dyspnea or risk factors for PH [2,14,21,22] .

Findings of PH on CXR include enlargement of the central pulmonary arteries, with or without rapid tapering (pruning), and right heart chamber enlargement [3,10,14,22,23] . A measurement of the right interlobar artery $\scriptstyle>15\,\mathrm{\mm}$ in women $(>\!16\ensuremath{\,\mathrm{~mm}}$ in men) at the hilum is suggestive of PH [10] . In one prospective study on patients with PAH, the CXR demonstrated prominence of the main pulmonary artery in $90\%$ of patients, enlarged hilar vessels in $80\%$ , and decreased peripheral vessels in $51\%$ . All three of these abnormalities were seen in $42\%$ of the patients in the study [24] . Another study by Schmidt et al [17] on patients with PH from chronic thromboembolic disease showed an enlarged main pulmonary artery in $96\%$ of patients. Additionally, CXR may show fi ndings of diffuse lung diseases that can be associated with PH, such as interstitial lung disease, emphysema, and so on [10,21] .

Echocardiography Transthoracic Resting. Transthoracic Doppler echocardiography should always be performed in the initial evaluation whenever PH is suspected. Doppler echocardiography has a sensitivity of $79\%$ to $100\%$ and

speci fi city of $68\%$ to $98\%$ in detecting moderate PH. However, detection of mild PH is more limited [14,25] . Continuous-wave Doppler measurement of the peak tricuspid regurgitation velocity is used in combination with additional echocardiographic signs suggestive of PH to assign an echocardiographic probability of PH (low, intermediate, or high) [2,26] . Additional echocardiographic variables that may be suggestive of PH include diameter of the pulmonary artery, estimate of right atrial pressure, increased right atrial size, abnormal bowing and motion of the interventricular septum, blood fl ow velocity and pattern out of the right ventricle, right ventricular hypertrophy, and increased right ventricle size compared with the left ventricle [10,27-30] .

Transthoracic Doppler echocardiography is also useful for evaluating cardiac anatomy, valvular function and morphology, left ventricular systolic and diastolic dysfunction, and the presence of pericardial effusion. An echocardiographic contrast or “ bubble ” study using agitated saline may be useful for detecting intracardiac shunts [11] . Echocardiographic evaluation of the right ventricular myocardial performance index and tricuspid annular plane systolic excursion index should be measured concomitantly with mean pulmonary artery pressure (PAP), as PAP in patients with advanced PH may decrease with deterioration of right ventricular function [31] . Studies have shown that real-time 3-D echocardiography is superior in evaluation of right ventricular volumes and ejection fraction compared with conventional 2-D echocardiography [29,32] .

RHC is necessary for con fi rmation of PH in patients with intermediate or high echocardiographic probability of PH before treatment initiation. As mentioned earlier, transthoracic Doppler echocardiography is not reliable to screen for mild, asymptomatic PH. Additional limits of transthoracic Doppler echocardiography include acoustic window restrictions (particularly in patients with underlying lung disease), limitations due to body habitus, and operator dependence. Further evaluation with additional noninvasive examinations including CT and MRI may be obtained. RHC is available for further evaluation if noninvasive examinations fail to yield a diagnosis [2,10] .

Patients at high risk for development of PAH may bene fi t from screening using transthoracic Doppler echocardiography [11] . At-risk patients include (1) individuals with a known genetic mutation associated with PAH or a fi rst-degree relative with idiopathic PAH (IPAH), (2) patients with scleroderma spectrum of disease, (3) patients with congenital heart disease and systemic-to-pulmonary

shunts, and (4) patients with portal hypertension before liver transplantation [33] . However, as noted earlier, mild, asymptomatic PH is not reliably detected by Doppler echocardiography, and if there is high clinical suspicion, RHC may be pursued [2,28] .

Transesophageal Echocardiography. Transesophageal echocardiography (TEE) is a more invasive technique than resting transthoracic echocardiography. It requires conscious sedation. Although complications of TEE are rare when performed by an experienced echocardiographer, pharyngeal and esophageal trauma have been reported. In general, PH is well assessed by resting transthoracic echocardiography. TEE may be considered to further evaluate for the presence of congenital shunts such as sinus venosus defect and anomalous pulmonary venous return. However, noninvasive techniques such as cardiac MRI and CT can also easily assess these entities and are recommended over TEE [2] .

V/Q Scans. The algorithm recommended by the American College of Cardiology working group recommends V/Q scanning in all patients with unexplained PH, primarily to assess for CTEPH [2,34] . V/Q scans are the examination of choice in evaluating for CTEPH and differentiating CTEPH from other causes of PH [35,36] . V/Q scanning demonstrated a sensitivity of $90\%$ to $100\%$ and speci fi city of $94\%$ to $100\%$ for differentiation between IPAH and CTEPH [37] . A normal or low-probability scan essentially excludes the diagnosis of CTEPH with a sensitivity of $90\%$ to $100\%$ and a speci fi city of $94\%$ to $100\%$ . The V/Q scan may be normal in other causes of PH [2,10] .

A study by Tunariu et al [36] found that V/Q scintigraphy was more sensitive than multidetector CT pulmonary angiography (CTPA) in detecting chronic thromboembolic pulmonary disease amenable to surgery, with V/Q scans demonstrating a sensitivity of $96\%$ to $97.4\%$ and a speci fi city of $90\%$ to $95\%$ , compared with a sensitivity of $51\%$ and speci fi city of $99\%$ for multidetector CTPA. However, more recent studies using 40- or 64-row scanners have demonstrated sensitivities and speci fi cities of CTPA of $99\%$ to $100\%$ and $100\%$ , respectively [38] . MR can also be used to also assess ventilation and perfusion in centers with experience [39] .

CT and CT Angiography. Both CT and CTPA (CT angiography [CTA] chest/CTPA chest) are very useful studies in the evaluation of PH and characterization of associated changes in the pulmonary parenchyma as well as the cardiovascular system. A main pulmonary artery diameter of ${\ge}29\;\mathrm{mm}$ has been shown to be $87\%$ sensitive

and $89\%$ speci fi c, with a positive predictive value of $97\%$ , for PH [3,40] . However, additional studies have shown that the sensitivity and speci fi city of main pulmonary artery diameter can vary depending on the presence of lung disease, and a main pulmonary artery diameter ${<}29\,\mathrm{~mm}$ does not exclude PH [41-43] . PH is almost always present when the main pulmonary artery is larger than the adjacent ascending aorta (positive predictive value of $96\%$ ) [14,22] . Other fi ndings suggesting PH on CT/CTPA include a ratio of segmental pulmonary artery to accompanying bronchus ${>}1{:}1$ , mosaic attenuation of the lungs, pericardial thickening or effusion, enlargement of the right ventricle, and straightening of the interventricular septum. Enlargement of the bronchial arteries to a diameter of $\mathord{>}1.5~\mathrm{mm}$ can also be seen in patients with PH [3,22,40,44-46] . Extrinsic compression of the left main coronary artery by a dilated main pulmonary artery, an uncommon fi nding in PH, has also been reported on CT [47] . In end-stage PH, linear calci fi cations along central pulmonary artery walls compatible with atheromatous plaques may be present [14,22] . A small retrospective study by Chan et al [48] has shown that additional CT predictors of PH include right ventricular free wall thickness ${\ge}6~\mathrm{mm}$ , right ventricular lumen/left ventricular lumen ${\geq}1.28$ , and true right and left descending pulmonary artery diameters of 16 and $21\,\mathrm{\mm}$ , respectively. Subsequent evaluation with RHC is necessary for con fi rmation of PH.

There are many etiologies of PH, including chronic pulmonary embolism (PE), IPAH, PCH, PVOD, left-toright shunts, and congenital heart disease, as well as many diffuse lung diseases. Many of these diseases are best characterized by cross-sectional imaging, particularly CT/ CTPA, and many have additional speci fi c imaging fi ndings on CT/CTPA in addition to the fi ndings compatible with PH that have been discussed earlier.

CTPA is regularly used to evaluate for thromboembolic disease and is the standard of care at most institutions [22,49] . Compared with V/Q scanning, it is also an accurate diagnostic modality for CTEPH, with a sensitivity of $83\%$ to $100\%$ and a speci fi city of $89\%$ to $97\%$ [35,50] . CT fi ndings of CTEPH include CT fi ndings of PH (detailed earlier), as well as fi ndings of chronic PE, which include eccentric thrombus within the pulmonary arteries, recanalized thrombus with or without calci fi cation, abrupt cutoff and narrowing of an affected pulmonary artery, and thin linear webs within the affected arteries. Mosaic attenuation of the lung parenchyma is often present as well, with decreased

vessel size in the areas of low attenuation [22,51-58] . Enlarged bronchial arteries and systemic arteries are commonly present [35] . Bronchiectasis has also been reported [59] . Small studies have shown that dualenergy CT perfusion and angiography is also both highly sensitive and speci fi c in diagnosis of CTEPH and can assess both anatomy and perfusion in CTEPH [60-62] .

IPAH is an uncommon disease characterized by a plexiform lesion, which is a network of capillary-like channels in the wall of a dilated muscular pulmonary artery. CT fi ndings of IPAH include enlarged pulmonary arteries, small pericardial effusion, and centrilobular ground-glass attenuation surrounding the torturous and enlarged centrilobular arterioles. Subtle mosaic attenuation may be present. Sometimes small centrilobular nodules can also be seen on CT [22,63-65] .

There are two rare diseases (PCH and PVOD) associated with PH that can be suggested by fi ndings on CT/ CTPA. PCH is a diffuse proliferation of capillaries throughout the pulmonary interstitium that is associated with obstruction of venules. CT will show enlarged pulmonary arteries, centrilobular ground-glass nodules, and interlobular septal thickening [14,66-68] . PVOD is a disease that results from pulmonary vein intimal fi brosis and subsequent pulmonary vein thrombosis. This causes pulmonary venous hypertension and edema and ultimately PH as the increased pulmonary vascular pressure backs up into the main pulmonary artery. CT will show enlarged pulmonary arteries, pleural effusion, and interlobular septal thickening. The left atrium is normal in size, a key feature distinguishing PVOD from left heart mitral valve disease. Mediastinal lymph node enlargement has also been reported. PCH and PVOD both often require surgical biopsy for de fi nitive diagnosis [14,66,69-71] .

Congenital heart disease as well as left-to-right shunts including atrial septal defect, ventricular septal defect, patent ductus arteriosus, and anomalous pulmonary venous return can be diagnosed with CTPA [14] , although MR is the preferred modality for these diseases.

Diffuse lung diseases associated with PH include interstitial lung disease, emphysema, sarcoidosis, connective tissue disease, and pulmonary Langerhans cell histiocytosis. High-resolution CT is indicated for evaluating diffuse lung disease and for the screening of patients with chronic unexplained dyspnea (see the ACR Appropriateness Criteria “ Chronic Dyspnea — Suspected Pulmonary Origin ” [72] and “ Dyspnea — Suspected Cardiac Origin ” [73] ). In many cases, high-resolution CT may obviate the need for open lung biopsy.

For the purposes of distinguishing between CT and CTA, ACR Appropriateness Criteria topics use the de fi - nition in the Practice Parameter for the Performance and Interpretation of Body Computed Tomography Angiography (CTA) [74] : “ 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 de fi nitions that CMS has applied to the Current Procedural Terminology codes.

MRI and MR Angiography. MRI is another excellent noninvasive imaging study for the evaluation of PH and is the best noninvasive imaging examination for the evaluation of right ventricular morphology and function. MRI should be performed at centers with experience. Both cardiac MRI and pulmonary MR angiography (MRA) show morphologic fi ndings of PH similar to those seen on CT/CTPA: pulmonary artery enlargement and pruning of peripheral vasculature on MRA and right ventricular hypertrophy and dilation as well as straightening of the interventricular septum on cardiac MRI [1,4,38,75-78] . The combination of MRA and MR perfusion imaging of the lung can also reliably diagnose CTEPH [1,4,35,38,79] . MRI and MRA are often used to follow patients with known PH to assess for early changes in right ventricular function.

MR cine imaging is the gold standard to evaluate right ventricular function and size and can evaluate for right ventricular wall motion changes seen in PH. Right and left ventricular mass can also be accurately determined [80] , which can then be used to calculate a ventricular mass index (right ventricular mass/left ventricular mass). A ventricular mass index that is ${\tt>}0.6$ is compatible with PH [3,81] . Functional abnormalities seen in cardiac remodeling secondary to PH include right ventricular hypokinesis, leftward bowing and/or paradoxical movement of the interventricular septum, right ventricular dysfunction (increased end-diastolic volume, reduced ejection fraction, reduced cardiac index, reduced stroke volume), and pulmonary and tricuspid insuf fi ciency [1,4,77,81-85] .

Phase-contrast imaging techniques can measure average blood fl ow velocity of the main pulmonary artery,

which correlates with mean pulmonary arterial pressure. Decreased pulmonary artery blood fl ow velocity correlates to increased vascular resistance [10,81] . A small study by Kreitner et al [86] has suggested that estimation of mean pulmonary arterial pressure from high-temporalresolution phase-contrast MRI is possible, but further investigation in a larger population is still needed. Heterogeneous fl ow in the main pulmonary artery as well as decreased pulmonary artery distensibility can be seen in PH. Pulmonary artery distensibility is the change in the pulmonary artery area throughout the cardiac cycle. A decrease in pulmonary artery distensibility is an early sign of increased pulmonary vascular resistance and poor outcomes in patients with PH [10,80,81,83,87,88] . Additionally, it can measure right ventricular stroke volume and cardiac output and can quantify intracardiac and extracardiac shunts by measuring the pulmonary to systemic fl ow ratio [1,3,4,22,89] . MRI is an excellent tool (sensitivity of $93\%$ to $100\%$ and speci fi city of $87\%$ to $100\%$ ) to detect and quantify cardiovascular shunts that are dif fi cult to identify on echocardiography, including sinus venosus atrial septal defects, patent ductus arteriosus, and anomalous pulmonary venous return [14,90-92] .

Delayed-contrast MRI typically shows enhancement of the right ventricle at its insertion points into the interventricular septum in PH [1,3,80,81,83] . Recently, 4-D fl ow MRI techniques have been used to noninvasively measure hemodynamic alterations that occur with PH: decreased wall shear stress, increased tricuspid regurgitation velocity, and abnormal vortex blood fl ow pattern within the main pulmonary artery that is associated with early-onset systolic retrograde fl ow [93-96] . Small studies have shown that MRI can also be used as a noninvasive method for obtaining functional information to monitor treatment response and the long-term effects of vasodilator therapy [22,97,98] .

The advantages of MRI include its lack of ionizing radiation and its ability to provide high – spatial resolution images in any plane without the need of an imaging “ window, ” as echocardiography requires. The major contraindication to MRI is the presence of speci fi c ferromagnetic and/or conducting implants such as cardiac pacemakers, although MRI has been performed safely in patients with pacemakers under rigorous safety conditions [10,99] . Contraindications to intravenous gadolinium chelate contrast, which is required for certain sequences, include allergy to gadolinium and renal dysfunction [100] .

Limitations of MRI include motion and respiratory artifacts that may degrade image quality, particularly for

certain motion-sensitive sequences; long acquisition times; and the need for sedation in patients with claustrophobia. Given its high diagnostic sensitivity and speci fi city and lack of ionizing radiation, MRI may be used as an adjunct or provide a comprehensive alternative to current fi rst-line or invasive examinations at many tertiary centers with experience. This is particularly important for young patients for whom the risks from repeated radiation exposures are greater and for patients with signi fi cant comorbidities that result in greater risk from repeated RHCs.

RHC. RHC is the gold standard for the diagnosis of PAH and is typically performed after all other noninvasive examinations have been completed to con fi rm the diagnosis of PH as well as assess its severity. At experienced institutions, it has morbidity and mortality rates of $1.1\%$ and $0.055\%$ , respectively [2,11,101] .

RHC directly measures PAP and cardiac function. A pulmonary vascular resistance of ${>}3$ Wood units is necessary to establish a diagnosis of PAH. Vasoreactivity testing of the pulmonary circulation may also be performed at the time of RHC in selected patients with IPAH, heritable PAH, and drug-induced PAH to determine candidacy for calcium channel blocker treatment [2,102] .

Pulmonary Angiography. Before multidetector CT, catheter pulmonary angiography was considered the reference standard for assessing PE. Studies have demonstrated that CTPA is as reliable as digital subtraction angiography in the evaluation of CTEPH [55] . Findings of CTEPH on CTPA and catheter pulmonary angiography include webs or bands with or without stenotic dilatation, intimal irregularities, and abrupt narrowing or occlusion of segmental or larger vessels. Catheter pulmonary angiography is now used almost exclusively for thrombolysis.

FDG-PET/CT. FDG-PET/CT allows in vivo imaging of metabolic processes and is complementary to the structural/anatomic information provided by cross-sectional imaging modalities such as CT and MRI. FDG-PET/ CT is well established for the diagnosis and follow-up of malignancy but is also becoming a valuable imaging modality for the characterization and diagnosis of various in fl ammatory conditions [103,104] . The use of FDGPET/CT in the evaluation of PH is extremely limited. There is increased FDG uptake in the lungs of patients with IPAH as well as within the right ventricular myocardium in patients with right ventricular dysfunction secondary to PH [83,105-107] . A study by Tatebe et al

[108] shows poorer prognosis in PH patients with a standardized uptake value of ${\geq}8.3$ in the region of the right ventricular free wall. Gated FDG-PET/CT is an available method that evaluates both right ventricular function and myocardial glucose metabolism [109] . The main potential utility of FDG-PET/CT in patients with PH is in distinguishing rare mimics of CTEPH, including pulmonary artery sarcoma and medium- to large-vessel vasculitis such as Takayasu arteritis, both of which will demonstrate increased FDG uptake [3,110-112] . Differentiating CTEPH from these rare mimics is critical because of important treatment implications [113,114] .

SUMMARY OF RECOMMENDATIONS

n CXR is an appropriate study in the initial diagnostic evaluation of PH, based on multiple studies. It has an overall high sensitivity and speci fi city for detecting the presence of PH. However, CXR is known to be insensitive in the detection of mild PH, and therefore a normal CXR cannot exclude it. Further imaging evaluation is recommended if the CXR is normal and there are persistent unexplained symptoms such as dyspnea or other risk factors for PH. n Resting TTE is the screening test of choice in the initial evaluation of suspected PH and should always be performed in the evaluation of suspected PH. Similar to CXR, it can be limited in the evaluation of mild, asymptomatic PH. n TEE is more invasive than TTE. Although it can also evaluate for congenital shunts in addition to PH, noninvasive studies such as CT and MRI can do this as well and are recommended over TEE. n V/Q scans should be obtained in all patients with PH to assess for CTEPH. A V/Q scan is the examination of choice to evaluate for CTEPH. CTA (CTPA) and MRA are additional tools that are also available to evaluate for CTEPH. n CT chest with IV contrast and CTA (CTPA) chest with IV contrast are excellent noninvasive imaging examinations that can characterize fi ndings of PH as well as often suggest an underlying cause. In some situations (for example, if there is suspicion for occult interstitial lung disease), an HRCT without IV contrast may also be useful. n MRI is an excellent noninvasive imaging examination that readily characterizes fi ndings associated with PH. It is the best available noninvasive examination to evaluate right ventricular morphology and function, which are closely associated with PH prognosis. n RHC is the gold standard for the diagnosis of PH and should be performed in all cases of suspected PH after noninvasive examinations are completed to con fi rm the diagnosis prior to treatment initiation. n Catheter pulmonary angiography is now primarily reserved for thrombolysis. It can be performed when considering surgical or percutaneous embolectomy. n The use of FDG-PET/CT in evaluating PH is extremely limited. Its main potential utility is in distinguishing rare mimics of CTEPH, such as pulmonary artery sarcoma.

SUMMARY OF EVIDENCE

Of the 115 references cited in the ACR Appropriate ness Criteria Suspected Pulmonary Hypertension document, all are categorized as diagnostic references, including 12 good-quality studies and 22 quality studies that may have design limitations. There are 79 references that may not be useful as primary evidence. There are 2 references that are meta-analysis studies.

The 115 references cited in the ACR Appropriateness Criteria Suspected Pulmonary Hypertension document were published from 1962 to 2016.

While there are references that report on studies with design limitations, 12 good-quality studies provide good evidence.

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 speci fi ed for adults (see Table 1 ). Additional information regarding radiation dose assessment for imaging examinations can be found in the ACR Appropriateness Criteria Radiation Dose Assessment Introduction document [115] .

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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Drug, toxin, and radiation induced 1 0 .4 Associated with: 1 0 .4.1 Connective tissue disease 1 0 .4.2 HIV infection Group $1^{\prime\prime}$ . Persistent pulmonary hypertension of the newborn Group 2. Pulmonary hypertension due to left heart disease 2.1 Left ventricular systolic dysfunction 2.2 Left ventricular diastolic dysfunction 2.3 Valvular disease 2.4 Congenital/acquired left heart in fl ow/out fl ow tract obstruction and congenital cardiomyopathies 2.5 Congenital/acquired pulmonary vein stenosis Group 3. Pulmonary hypertension due to lung dis eases and/or hypoxia 3.1 Chronic obstructive pulmonary disease 3.2 Interstitial lung disease 3.3 Other pulmonary diseases with mixed restrictive and obstructive pattern 3.4 Sleep-disordered breathing 3.5 Alveolar hypoventilation disorders 3.6 Chronic exposure to high altitude 3.7 Developmental lung diseases Group 4. Chronic thromboembolic pulmonary hy pertension and other pulmonary artery obstructions 4.1 Chronic thromboembolic pulmonary hypertension 4.2 Other pulmonary artery obstructions 4.2.1 Angiosarcoma 4.2.2 Other intravascular tumors 4.2.3 Arteritis 4.2.4 Congenital pulmonary artery stenoses 4.2.5 Parasites (hydatidosis) Group 5. Pulmonary hypertension with unclear and/ or multifactorial mechanisms 5.1 Hematological disorders: chronic hemolytic anemia, myeloproliferative disorders, splenectomy 5.2 Systemic disorders: sarcoidosis, pulmonary histiocy tosis, lymphangioleiomyomatosis, neuro fi bromatosis 5.3 Metabolic disorders: glycogen storage disease, Gaucher disease, thyroid disorders 5.4 Others: pulmonary tumoral thrombotic micro angiopathy, fi brosing mediastinitis, chronic renal failure (with/without dialysis), segmental pulmonary hypertension

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