Ventilation-Perfusion Scan: A Primer for Practicing Radiologists.

Lung scintigraphy, or ventilation-perfusion (V/Q) scan, is one of the commonly performed studies in nuclear medicine. Owing to variability in clinical applications and different departmental workflows, many trainees are not comfortable interpreting the results of this study. This article provides a simplified overview of V/Q imaging, including a review of its technique, interpretation methods, and established and emerging clinical applications. The authors review the role of V/Q imaging in evaluation of acute and chronic pulmonary embolism, including the role of SPECT/CT and comparing V/Q scan with CT angiography. In addition, a variety of other applications of pulmonary scintigraphy are discussed, including congenital heart disease, pretreatment planning for lung cancer and emphysema, posttransplant imaging for bronchiolitis obliterans, and less common vascular and nonvascular pathologic conditions that may be detected with V/Q scan. This article will help radiologists and residents interpret the results of V/Q scans and understand the various potential clinical applications of this study. Online supplemental material is available for this article. ©RSNA, 2021.

Patient Exposure from Radiologic and Nuclear Medicine Procedures in the United States: Procedure Volume and Effective Dose for the Period 2006-2016.

Background Comprehensive assessments of the frequency and associated doses from radiologic and nuclear medicine procedures are rarely conducted. The use of these procedures and the population-based radiation dose increased remarkably from 1980 to 2006. Purpose To determine the change in per capita radiation exposure in the United States from 2006 to 2016. Materials and Methods The U.S. National Council on Radiation Protection and Measurements conducted a retrospective assessment for 2016 and compared the results to previously published data for the year 2006. Effective dose values for procedures were obtained from the literature, and frequency data were obtained from commercial, governmental, and professional society data. Results In the United States in 2006, an estimated 377 million diagnostic and interventional radiologic examinations were performed. This value remained essentially the same for 2016 even though the U.S. population had increased by about 24 million people. The number of CT scans performed increased from 67 million to 84 million, but the number of other procedures (eg, diagnostic fluoroscopy) and nuclear medicine procedures decreased from 17 million to 13.5 million. The number of dental radiographic and dental CT examinations performed was estimated to be about 320 million in 2016. Using the tissue-weighting factors from Publication 60 of the International Commission on Radiological Protection, the U.S. annual individual (per capita) effective dose from diagnostic and interventional medical procedures was estimated to have been 2.9 mSv in 2006 and 2.3 mSv in 2016, with the collective doses being 885 000 and 755 000 person-sievert, respectively. Conclusion The trend from 1980 to 2006 of increasing dose from medical radiation has reversed. Estimated 2016 total collective effective dose and radiation dose per capita dose are lower than in 2006. © RSNA, 2020 See also the editorial by Einstein in this issue.

American Thoracic Society documents: an official American Thoracic Society/Society of Thoracic Radiology Clinical Practice Guideline--Evaluation of Suspected Pulmonary Embolism in Pregnancy.

BACKGROUND: Pulmonary embolism (PE) is a leading cause of maternal mortality in the developed world. Along with appropriate prophylaxis and therapy, prevention of death from PE in pregnancy requires a high index of clinical suspicion followed by a timely and accurate diagnostic approach. METHODS: To provide guidance on this important health issue, a multidisciplinary panel of major medical stakeholders was convened to develop evidence-based guidelines for evaluation of suspected pulmonary embolism in pregnancy using the Grades of Recommendation, Assessment, Development, and Evaluation (GRADE) system. In formulation of the recommended diagnostic algorithm, the important outcomes were defined to be diagnostic accuracy and diagnostic yield; the panel placed a high value on minimizing cumulative radiation dose when determining the recommended sequence of tests. RESULTS: Overall, the quality of the underlying evidence for all recommendations was rated as very low or low with some of the evidence considered for recommendations extrapolated from studies of the general population. Despite the low quality evidence, strong recommendations were made for three specific scenarios: performance of chest radiography (CXR) as the first radiation-associated procedure; use of lung scintigraphy as the preferred test in the setting of a normal CXR; and performance of computed-tomographic pulmonary angiography (CTPA) rather than digital subtraction angiography (DSA) in a pregnant woman with a nondiagnostic ventilation-perfusion (V/Q) result. DISCUSSION: The recommendations presented in this guideline are based upon the currently available evidence; availability of new clinical research data and development and dissemination of new technologies will necessitate a revision and update.

An official American Thoracic Society/Society of Thoracic Radiology clinical practice guideline: evaluation of suspected pulmonary embolism in pregnancy.

BACKGROUND: Pulmonary embolism (PE) is a leading cause of maternal mortality in the developed world. Along with appropriate prophylaxis and therapy, prevention of death from PE in pregnancy requires a high index of clinical suspicion followed by a timely and accurate diagnostic approach. METHODS: To provide guidance on this important health issue, a multidisciplinary panel of major medical stakeholders was convened to develop evidence-based guidelines for evaluation of suspected pulmonary embolism in pregnancy using the Grades of Recommendation, Assessment, Development, and Evaluation (GRADE) system. In formulation of the recommended diagnostic algorithm, the important outcomes were defined to be diagnostic accuracy and diagnostic yield; the panel placed a high value on minimizing cumulative radiation dose when determining the recommended sequence of tests. RESULTS: Overall, the quality of the underlying evidence for all recommendations was rated as very low or low, with some of the evidence considered for recommendations extrapolated from studies of the general population. Despite the low-quality evidence, strong recommendations were made for three specific scenarios: performance of chest radiography (CXR) as the first radiation-associated procedure; use of lung scintigraphy as the preferred test in the setting of a normal CXR; and performance of computed-tomographic pulmonary angiography (CTPA) rather than digital subtraction angiography (DSA) in a pregnant woman with a nondiagnostic ventilation-perfusion (V/Q) result. DISCUSSION: The recommendations presented in this guideline are based upon the currently available evidence; availability of new clinical research data and development and dissemination of new technologies will necessitate a revision and update.

Effects of low level radiation-what's new?

A comprehensive review of the effects of exposure to low levels of ionizing radiation, BEIR VII-Phase 2: Health Risks From Exposure to Low Levels of Ionizing Radiation, was published in 2006. The BEIR (Biological Effects of Ionizing Radiation) reports are a series of publications by the National Academy of Sciences. The last BEIR report on the effects of low level radiation, BEIR V, was published in 1990. To update the risk estimates for exposure to low levels of ionizing radiation, the BEIR committee reviewed recent epidemiologic studies of the atomic bomb survivors, as well as recent studies of populations exposed to radiation from diagnostic and therapeutic medical studies, from occupational exposures and from exposure due to releases of radioactive materials into the environment. Additional increasingly sophisticated epidemiologic studies continue to be published. BEIR VII reconfirmed that the linear no threshold model is the most practical model to estimate radiation risks, especially for radiation protection purposes. The updated risk estimates have not changed significantly from the BEIR V estimates, but the confidence intervals have narrowed as the result of the availability of additional data. The effects of low doses of radiation should be of particular interest to medical professionals because radiation exposure from diagnostic medical studies is, by far, the largest source of radiation exposure from human activity. One recommendation of the BEIR VII report is to perform epidemiologic studies of patients, especially children, who have been exposed to radiation as part of their care. A large, sophisticated epidemiologic study will likely be able to detect an increase in cancer risk. The purpose of this article is to highlight the contents of this important publication with particular emphasis on what is new.

Concurrent PET/CT with an integrated imaging system: intersociety dialogue from the joint working group of the American College of Radiology, the Society of Nuclear Medicine, and the Society of Computed Body Tomography and Magnetic Resonance.

Rapid advances in imaging technology are a challenge for health care professionals, who must determine how best to use these technologies to optimize patient care and outcomes. Hybrid imaging instrumentation, combining 2 or more new or existing technologies, each with its own separate history of clinical evolution, such as PET and CT, may be especially challenging. CT and PET provide complementary anatomic information and molecular information, respectively, with PET giving specificity to anatomic findings and CT offering precise localization of metabolic activity. Historically, the acquisition and interpretation of the 2 image sets have been performed separately and very often at different times and locales. Recently, integrated PET/CT systems have become available; these systems provide PET and CT images that are acquired nearly simultaneously and are capable of producing superimposed, coregistered images, greatly facilitating interpretation. As the implementation of this integrated technology has become more widespread in the setting of oncologic imaging, questions and concerns regarding equipment specifications, image acquisition protocols, supervision, interpretation, professional qualifications, and safety have arisen. This article summarizes the discussions and observations surrounding these issues by a collaborative working group consisting of representatives from the American College of Radiology, the Society of Nuclear Medicine, and the Society of Computed Body Tomography and Magnetic Resonance.

ACR Appropriateness Criteria® pretreatment evaluation and follow-up of endometrial cancer.

Endometrial cancer is the most common gynecologic and the fourth most common malignancy in women in the United States. Cross-sectional imaging plays a vital role in pretreatment assessment of endometrial cancers and should be viewed as a complementary tool for surgical evaluation and planning of these patients. Although transvaginal US remains the preferred examination for the screening purposes, MRI has emerged as the modality of choice for the staging of endometrial cancer and imaging assessment of recurrence or treatment response. A combination of dynamic contrast-enhanced and diffusion weighted MRI provides the highest accuracy for the staging. Both CT and MRI perform equivalently for assessing nodal involvement or distant metastasis. PET-CT is more appropriate for assessing lymphadenopathy in high-grade FDG-avid tumors or for clinically suspected recurrence after treatment. An appropriate use and guidelines of imaging techniques in diagnosis, staging, and detection of endometrial cancer and treatment of recurrent disease are reviewed.The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed every two years by a multidisciplinary expert panel. The guideline development and review include an extensive analysis of current medical literature from peer reviewed journals and the application of a well-established consensus methodology (modified Delphi) to rate the appropriateness of imaging and treatment procedures by the panel. In those instances where evidence is lacking or not definitive, expert opinion may be used to recommend imaging or treatment.

ACR Appropriateness Criteria® clinically suspected adnexal mass.

Adnexal masses are a common problem clinically and imaging-wise, and transvaginal US (TVUS) is the first-line imaging modality for assessing them in the vast majority of patients. The findings of US, however, should be correlated with the history and laboratory tests, as well as any patient symptoms. Simple cysts are uniformly benign, and most warrant no further interrogation or treatment. Complex cysts carry more significant implications, and usually engender serial ultrasound(s), with a minority of cases warranting a pelvic MRI.Morphological analysis of adnexal masses with gray-scale US can help narrow the differential diagnosis. Spectral Doppler analysis has not proven useful in most well-performed studies. However, the use of color Doppler sonography adds significant contributions to differentiating between benign and malignant masses and is recommended in all cases of complex masses. Malignant masses generally demonstrate neovascularity, with abnormal branching vessel morphology. Optimal sonographic evaluation is achieved by using a combination of gray-scale morphologic assessment and color or power Doppler imaging to detect flow within any solid areas.The ACR Appropriateness Criteria® are evidence-based guidelines for specific clinical conditions that are reviewed every two years by a multidisciplinary expert panel. The guideline development and review include an extensive analysis of current medical literature from peer reviewed journals and the application of a well-established consensus methodology (modified Delphi) to rate the appropriateness of imaging and treatment procedures by the panel. In those instances where evidence is lacking or not definitive, expert opinion may be used to recommend imaging or treatment.

ACR appropriateness criteria staging and follow-up of ovarian cancer.

Imaging is used to detect and characterize adnexal masses and to stage ovarian cancer both before and after initial treatment, although the role for imaging in screening for ovarian cancer has not been established. CT and MRI have been used to determine the resectability of tumors, the candidacy of patients for effective cytoreductive surgery, the need for postoperative chemotherapy if debulking is suboptimal, and the need for referral to a gynecologic oncologist. Radiographic studies such as contrast enema and urography have been replaced by CT and other cross-sectional imaging for staging ovarian cancer. Contrast-enhanced CT is the procedure of choice for preoperative staging of ovarian cancer. MRI without and with contrast may be useful after equivocal CT, but is usually not the best initial procedure for ovarian cancer staging. Fluorine-18-2-fluoro-2-deoxy-D-glucose-PET/CT may not be needed preoperatively, but its use is appropriate for detecting and defining post-treatment recurrence. Ultrasound is useful for evaluating adnexal disease, but has limited utility for staging ovarian cancer. The ACR Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed every 2 years by a multidisciplinary expert panel. The guideline development and review include an extensive analysis of current medical literature from peer-reviewed journals and the application of a well-established consensus methodology (modified Delphi) to rate the appropriateness of imaging and treatment procedures by the panel. In those instances where evidence is lacking or not definitive, expert opinion may be used to recommend imaging or treatment.

From the angio suite to the γ-camera: vascular mapping and 99mTc-MAA hepatic perfusion imaging before liver radioembolization--a comprehensive pictorial review.

Endovascular mapping and conjoint (99m)Tc-macroaggregated albumin ((99m)Tc-MAA) hepatic perfusion imaging provide essential information before liver radioembolization with (90)Y-loaded microspheres in patients with primary and secondary hepatic malignancies. The aims of this integrated procedure are to determine whether there is a risk for excessive shunting of (90)Y-microspheres to the lungs; to detect extrahepatic perfusion emerging from the injected vascular territory, which might lead to nontargeted radioembolization; to reveal incomplete coverage of the liver parenchyma involved by the tumor, which may be related to anatomic or acquired variants of the arterial vasculature; and to aid in calculation of the (90)Y-microsphere dose to be delivered to the liver. This pictorial essay presents an integrated comprehensive review of the anatomic, angiographic, and nuclear imaging aspects of planned liver radioembolization. The relevant anatomy of the liver, including the standard and the variant arterial vasculature, will be shown using digital subtraction angiography, SPECT/CT, contrast-enhanced CT, and anatomic illustrations. Technical details that will optimize the imaging protocols and important imaging findings will be discussed. From the angio suite to the γ-camera-the goal of this review is to help the reader better understand how the technical details of the angiographic procedure are reflected in the imaging findings of the (99m)Tc-MAA hepatic perfusion study. In addition, the reader should learn to better recognize the pertinent findings and their clinical implications. This knowledge will enable the reader to provide a more useful interpretation of this complex multidisciplinary procedure.

ACR Appropriateness Criteria® pretreatment planning of invasive cancer of the cervix.

The prognosis of cervical cancer is linked to lymph node involvement, and this is predicted clinically and pathologically by the stage of the disease, as well as the volume and grade of the tumor. Staging of cervical cancer based on International Federation of Gynecology and Obstetrics (FIGO) staging uses physical examination, cystoscopy, proctoscopy, intravenous urography, and barium enema. It does not include CT or MRI. Evaluation of the parametrium is limited in FIGO staging, and lymph node metastasis, an important prognostic factor, is not included in FIGO staging. The most important role for imaging is to distinguish stages Ia, Ib, and IIa disease treated with surgery from advanced disease treated with radiation therapy with or without chemotherapy. This article reviews the current role of imaging in pretreatment planning of invasive cervical cancer. The ACR Appropriateness Criteria(®) are evidence-based guidelines for specific clinical conditions that are reviewed every 2 years by a multidisciplinary expert panel. The guideline development and review include an extensive analysis of current medical literature from peer-reviewed journals and the application of a well-established consensus methodology (modified Delphi) to rate the appropriateness of imaging and treatment procedures by the panel. In those instances in which evidence is lacking or not definitive, expert opinion may be used to recommend imaging or treatment.