How Soon Should a 5 Mm Nodule on Lower Left Lobe of Lung Be X Rayed Again

Introduction

The likelihood of malignancy in a pulmonary nodule correlates strongly with both its size and its growth rate, allowing for boosted factors, such equally a history of prior lung cancer or extrathoracic malignancy (ane). Thus, authentic measurement of nodule size is crucial for 3 reasons: (a) to determine the run a risk for malignancy at baseline computed tomography (CT), (b) to correctly allocate patients with nodules to available management algorithms, and (c) to detect whatsoever alter in size on follow-upward CT images, which might take bearing on the likelihood of malignancy or might influence treatment in patients who are existence monitored during therapy. Although nodule size is a key criterion in current recommendations for nodule management (2–4), there is relatively little data about how best to arroyo lung nodule measurement in clinical practice, which is the main motivation for these recommendations.

Size and growth of pulmonary nodules tin be determined by measuring their bore or volume. Measurement of the nodule diameter with electronic calipers is convenient to perform and is currently the most widely used routine clinical arroyo. Nodule volumes can be measured either manually by delineating nodule boundaries or semiautomatically by using software that detects CT attenuation thresholds. Semiautomatic volume determination typically requires either remote workstations or dedicated software applications; hence, information technology is currently not widely used in routine clinical practice (five). Automated partition is also the initial pace underlying approaches that mensurate nodule mass rather than size (6); this approach has been proposed for subsolid nodules and is however under investigation.

Contained of which nodule component is measured (solid component, ground-glass component, or both) and regardless of which technical approach is used, the resulting measurement volition be affected past a number of technical and observer-related factors. Moreover, series follow-up examinations of nodules are often performed with different CT units and are assessed by unlike radiologists using different technical acquisition and reconstruction parameters.

In the first role of this article, nosotros will nowadays our recommendations for measurement of the size of pulmonary nodules. These recommendations are organized effectually specific questions that are ofttimes raised in clinical practice and are presented together with respective answers. In the second part, we volition describe the technical factors, such as section thickness, reconstruction algorithms, and display window settings, that touch on these measurements. There is increasing evidence that the technical aspects of these factors are closely interrelated, with cantankerous-influences that are not yet fully understood (7,8). Although discussing them i by ane might announced overly simplistic, we promise that this incremental approach volition provide the reader with practically useful data to perform and interpret lung nodule measurements. In the third and terminal role of this article, we will highlight areas of uncertainty and ongoing investigation, focusing on questions that will need to exist addressed in future research, to make lung nodule measurements more accurate and clinically meaningful.

The electric current recommendations can exist used to measure pulmonary nodules on any given CT image. Even so, their use should also be adamant by the clinical circumstances. For instance, the recommendations are not intended to replace other measurement approaches, such as employ of Lung CT Screening Reporting and Data System or Response Evaluation Criteria in Solid Tumors, which are recommended for lung cancer screening and cess of handling response in oncologic imaging, respectively. Furthermore, if a different arroyo to nodule measurement was initially called at serial CT, this arroyo should be retained for the sake of consistency.

Given the frequency with which the size of pulmonary nodules is measured in clinical practise and given the variability of these measurements betwixt different observers (3,5,nine), we believe that the need for guidelines such equally these is evident. In developing these recommendations, the Fleischner Social club, as a multidisciplinary group of thoracic specialists, has weighed bachelor scientific evidence and expert consensus regarding current practise and hereafter developments. The following recommendations will mainly focus on transmission diameter measurements, which are the nigh widely used technique, at present. Nevertheless, given the rapid technical advances in recent years, especially with respect to the role of automated paradigm-based disease quantification, we anticipate that refinements and modifications to these recommendations will be forthcoming, as data continues to emerge from ongoing enquiry.

Part 1: Recommendations

The recommendations are summarized in Figure 1 and Tabular array E1 (online), organized by practical questions and the corresponding answers. The evidence grades for the individual recommendations shown are based on those adult past the American College of Breast Physicians (10).

Office ii: Technical and Observer-related Factors

Dimensions of a Pulmonary Nodule

The dimensions of a pulmonary nodule are measured differently past pathologists and radiologists. Whereas pathologists record only the maximum diameter of a nodule (11), radiologists take been expressing the dimensions of pocket-size (<10 mm) nodules as the average of the long- and curt-centrality measurements, notably when they are used for risk assessment (2,12). For larger nodules, particularly for staging, bidimensional measurements reporting both long- and short-centrality bore are the most ordinarily used (Figs 2, 3). Given the importance of nodule dimensions for direction recommendations and oncologic staging and the increasingly collaborative approach to pulmonary nodules in the fields of pathology and radiology (11,13,14), more inquiry is needed to establish which CT parameter about closely correlates with final stage and event.

Figure 2: — Effigy 2: Transverse CT sections of a solid nodule in the left lower lobe. A, The nodule is anatomically well divers. B, First, the maximal long-axis diameter is measured (sixteen mm, vertical arrow). Then, perpendicular to the long-axis measurement, the maximum short-axis bore is measured (14 mm, horizontal arrow). The boilerplate diameter of the nodule is fifteen mm. As detailed in the get-go recommendation, for purposes of risk interpretation, the dimension of small pulmonary nodules (<10 mm) should exist expressed as the average of maximal long-axis and perpendicular maximal short-axis measurements in the same plane. For larger nodules and masses (≥10 mm), long- and brusk-axis measurements should be recorded. Because the boilerplate diameter of this nodule is larger than x mm, both long- and brusk-axis measurements are given.

Figure 3: Transverse CT department of a pure basis-glass nodule in the left upper lobe. The aforementioned approach to nodule measurement described in Figure 2 applies in this image. The average diameter of the nodule is 17 mm.

Historically, the transition in radiology from using the maximum diameter to using the average of long- and short-axis diameters of small nodules for risk assessment occurred in the tardily 1990s, when the latter approach was adopted by the Early Lung Cancer Activeness Program (15). The same arroyo was described in the showtime management guidelines for pulmonary nodules published by the Fleischner Society (two). Finally, the American College of Radiology recommends use of the average dimension in its current CT lung cancer screening guidelines (sixteen). Although the National Lung Cancer Screening Trial used the maximum dimension rather than the average dimension (17,xviii), it has been suggested that this could have resulted in the misclassification of nodules as positive findings, most notably when the nodules were pocket-size (12,19). This is supported by the findings of three recent studies that retrospectively practical American Higher of Radiology Lung CT Screening Reporting and Data Arrangement criteria to large lung cancer screening cohorts; this reduced the false-positive charge per unit in all three studies (20–22). Nosotros continue to utilize the average dimensions in the upcoming revision of the Fleischner Society management guidelines for pulmonary nodules (23) because we assume that the average dimension likely correlates meliorate with tumor volume than one measurement, particularly in elongated nodules and in nodules where the short dimension is better defined (5). In practical terms, we recommend that the long-centrality diameter of a nodule be adamant offset and that thereafter, on the same CT department, the short centrality be measured perpendicular to the long axis. Recommendations for measuring spiculated and morphologically heterogeneous nodules are detailed in the side by side sections.

Measurement Unit of measurement

All measurements and their derivatives should be expressed to the nearest millimeter, which is the bones dimensional unit used in current nodule management guidelines (two,3,23). Although picture archiving and communication system consoles display measurements to the nearest 0.i mm, nosotros believe that this level of apparent precision is deceptive in the context of pulmonary nodules and given the multiple technical factors that influence their measurements. Consequently, a nodule with a long-centrality diameter of 4.5 mm should be rounded to 5 mm. As well, a nodule with a brusque-axis bore of 3.4 mm should exist rounded to three mm. Thus, the average bore of the nodule would be as follows: (five + 3)/two = 4 mm. If the mathematic boilerplate of the long- and short-axis diameters results in a number with a decimal fraction, it should similarly be rounded to the nearest whole millimeter. Recorded long- and brusque-axis diameters should also be rounded to the nearest millimeter. To estimate boilerplate bore based on manual measurements or obtained with automated measurement tools, fractional measurements may be considered, simply the event should nonetheless be recorded as a whole number.

Observer and Measurement Variability

Measurement of nodule diameter with electronic calipers is bailiwick to substantial inter- and intrareader variability (24–26) (Fig 4). Studies also suggest that variability increases with increasing complexity of nodule morphology, notably in office-solid nodules in which both the overall size and the size of the solid component are measured (3,5,9). One written report showed that when observers measured nodules twenty mm in diameter or smaller, the limits of inter- and intrareader variability were 1.73 mm and one.32 mm, respectively (26). This would hateful that a nodule could confidently exist determined to accept grown only if its diameter had increased beyond these limits. For case, because a 26% increase in bore of a spherical nodule corresponds to i book doubling (27), it could be falsely concluded that a nodule measuring 5.0 mm at baseline and so 6.3 mm at follow-up had doubled in volume, while this apparent growth could exist an artifact of measurement variability. In the same way, measurement variability may result in growing nodules being falsely determined to be stable.

Nodule volumetry may be less sensitive to variability depending on the method used. While the majority of volumetric measurements showed a variability of less than 10%, a maximum departure upward to approximately 27% has been reported in nodules with irregular margins and nonspherical morphology, causing more variable segmentation (28,29). When the mass of office-solid nodules is measured, inter- and intraobserver variability ranges from 217.5% to 11.eight% and from 28.4% to 9.4% (9,30). Information technology must be stressed that all of these reported results strongly depend on the software used and the characteristics of the written report lesions; this is a caveat that tin exist practical to any computerized quantification tool. Despite these generally encouraging results for semiautomated nodule book and mass measurements, it should be kept in mind that different software implementations can yield substantially different results (thirty,31) (Fig 5). Thus, from a applied perspective, it is desirable to perform sequential nodule evaluations with the identical software type and version.

Figure 4: — Effigy 4: Transverse CT sections of a office-solid nodule in the right upper lobe. A, The solid component of the nodule is ill divers, resulting in variability of measurements, as performed past two radiologists. The 2 long-axis diameters of the solid component were, B, 28 mm and, C, 14 mm. On the basis of the clinical implications, nosotros recommend use of the larger long-axis diameter. Only solid component measurements are shown in this figure; however, in clinical practise, nonsolid and solid components must be measured.

Figure 5: Segmentation and volumetry of a ground-drinking glass nodule with four unlike software packages. The nodule volumes calculated were, A, 2019, B, 2059, C, 1949, and, D, 1528 mm³, resulting in a maximum deviation of 531 mm³ betwixt measurements.

From a clinical perspective, several practical recommendations should be added. First, not every nodule needs to be measured, notably nodules of upward to three mm in size. Such small nodules are impossible to measure accurately, and observer variability is prone to produce erroneous and potentially misleading results, both at initial assessment and at follow-up (Fig 6). For such nodules, it is preferable to omit any caliper measurements and instead use the term micronodule to describe such a finding (32). Second, when performing sequential follow-up examinations of nodules, reference should always be made to the examination that first revealed the nodule, non merely the last available examination. In this regard, it is important to take into business relationship changes in nodule advent that may occur due to variations in inspiratory effort or the appearance of adjacent parenchymal abnormalities. Although the last available examination will be used every bit the reference to decide interval growth, comparisons with earlier prior examinations will increment confidence for long-term growth or stability when evaluating the evolution of a given nodule over time (Figs seven, 8). Third, when performing simple attenuation measurements past placing a region of interest over a nodule or when computing an attenuation profile forth a line through a nodule—for instance, to verify the presence of calcium or fat—this should be washed on images reconstructed without edge enhancement, typically the mediastinal soft-tissue series. This is because such attenuation measurements are prone to substantial inaccuracy in smaller nodules on sharpened (border-enhanced) images. Finally, measurements at follow-upwardly CT, which were acquired with techniques that were as like as possible to the original technique, should be made through the centroid of the nodule, which may not exist at the same anatomic level on sequential images, and by using the same orientation and location of caliper ballast points.

Figure 6: — Effigy 6: Transverse CT sections through nodules iii mm or smaller (pointer) in the, A, correct upper lobe, B, left upper lobe, and, C, right lower lobe. Such small nodules should non be measured, given inherent accuracy limitations and variability in determining whether the lesion is a solid, part-solid, or ground-glass nodule.

Figure 7: Sequential transverse CT sections through a solid nodule (arrow) in the right upper lobe. Boilerplate diameters of the nodule were, A, viii, B, 9, C, 11, and, D, 13 mm. Nodule growth is most obvious when we compare the earliest image with the most recent image. Surgery confirmed adenocarcinoma.

Figure 8: Sequential transverse CT sections through a ground-glass nodule (arrow) in the right upper lobe. Average diameters of the nodule are A, thirteen, B, xiv, and, C, 18 mm. Nodule growth is about obvious when we compare the primeval image with the about recent prototype.

Definition of Growth

Growth of a pulmonary nodule refers to an increase in size between two given CT examinations. In the context of bidimensional measurements, this will translate into an increase in bore. Because this is a 3-dimensional structure, yet, the increment in diameter should reflect an increase in nodule volume. If we assume a perfectly spherical geometry, a 26% increase in diameter will stand for to a doubling in the volume of a nodule (27). For case, a nodule that has increased in diameter by 2 mm (from 7 mm to 9 mm) betwixt two CT examinations has approximately doubled its volume. Given that diameter measurements vary past 1.73 mm across observers for nodules smaller than 2 cm (26), information technology appears reasonable to report growth when a change in measured bore of at least 2 mm is detected (actually at least ane.5 mm due to rounding). Use of this 2-mm threshold would reduce the likelihood of an incorrect diagnosis of growth when the apparent divergence in size is in fact within an expected range of dubiousness attributable to observer-related imprecision. Moreover, several relatively contempo studies have used a ii-mm threshold to define growth in both solid and part-solid nodules (33–35). A ii-mm threshold for growth was besides adopted by The British Thoracic Society in a contempo management recommendation (4). Furthermore, a threshold in millimeters is consistent with the principle of this recommendation to express nodule dimensions to the nearest millimeter and to avert any fractions of this unit (16). The ii-mm threshold for defining growth should be practical to both overall nodule size in both solid and part-solid nodules, too as to the solid component of a part-solid nodule. Although nodule growth is important, information technology is just one of several criteria used to guess cancer chance. Thus, it must be reemphasized that any alter in nodule size, including growth as defined previously, must always be interpreted together with other morphologic nodule characteristics, such as shape, borders, and internal texture (Fig 9). Finally, potential growth must be related to the interval between two CT examinations. A contempo recommendation has emphasized that accurateness of growth assessment increases with increasing intervals between examinations (four).

Figure 9: Sequential transverse CT sections of a nodule (arrow) in the left upper lobe. Although the average bore of the nodule has decreased from, A, 13 to, B, 8 mm, solid transformation and irregular margins make it suspicious. Later resection confirmed invasive adenocarcinoma.

Attenuation Measurements

At that place has been recent interest in using CT attenuation to assess the mass (which reflects the product of size and attenuation) rather than the size of pulmonary nodules (6). CT attenuation has likewise been used to assess growth of part-solid and nonsolid pulmonary nodules (36,37). Both overall attenuation and characteristics of the attenuation distribution within nodules have been used to differentiate adenocarcinoma subtypes, evaluate progression, and predict prognosis, notably in part-solid nodules (38–42). These studies provide promising preliminary insights into the potential of attenuation measurement every bit a tool to assess pulmonary nodules more accurately. However, the published series are small-scale, and no study derived a generalizable attenuation threshold or a metric that could be seamlessly translated into clinical do, and the proposed attenuation thresholds differ between studies (42–44). Thus, more evidence, notably with regard to measurement standardization and the pathologic implications of attenuation changes over time, is required before use of these techniques can be recommended for clinical lung nodule management.

CT Section Thickness

Several authors have studied the relationship between the accurateness of nodule measurement and CT section thickness (31,45–47). They consistently found that variability decreased with decreasing department thickness (31,45,46) and that the thinnest sections (unremarkably one mm) provided the most consequent results (47). The studies also found that the consequence of department thickness on variability was particularly pronounced for nodules smaller than 10 mm and for spiculated rather than polish nodules (31). This tin be explained past the increased fractional book averaging outcome for pocket-sized nodules when thicker sections are used, whereas the same effect is less astringent with larger nodules. From a practical perspective, these findings back up the utilize of contiguous thin (≤1.five mm) sections for the purpose of pocket-sized lung nodule measurements, equally recommended by current clinical guidelines (23). For spiculated nodules, only the nodule core should be measured, and the spiculations should non be function of the measured diameter (Fig 10). Thin sections also provide the reward of sufficient spatial resolution to allow for the visual assessment of morphologic nodule characteristics, such as shape and spiculations, that might refine the assessment of gamble and subtle changes over time (5) (Fig eleven).

Figure 10: A, Transverse CT section through a spiculated right lung nodule. B, Inclusion of spiculations into the measurement causes substantial overestimation of nodule size. C, The recommended approach is to measure only the solid core.

Figure 11: — Effigy 11: Transverse CT sections at the level of, *A, B,* a solid nodule (arrow) in the left upper lobe and, *C, D,* a part-solid nodule (arrow) in the left lower lobe. Solid and part-solid nodule margins are less well defined on A and C than on B and D. In addition, D better shows solid nodule components.

Orientation of the CT Section

Transverse reconstructions of the CT data set found the traditional ground for clinical reporting of thoracic CT examinations, and most nodule measurements can be performed through a transverse plane, with the maximal long axis and maximal perpendicular short centrality measured on the same paradigm. A given nodule, however, may be oriented in the lung parenchyma such that its biggest or smallest bore is aligned along a craniocaudal axis, making its true extent difficult to appraise on transverse images alone. In such cases, multiplanar reconstructions in the coronal and sagittal planes should be used to obtain a more accurate assessment of nodule size, with long and short axes again measured on the same epitome (Fig 12). In part-solid nodules, the CT sections should be chosen for measurements that brandish the largest portion of the overall nodule and the solid component, respectively. Often, these will not be displayed on the same department. In such cases, measurements should be performed on the sections that display the largest overall nodule bore and the largest bore of the solid component, respectively, and these sections should be identified in the radiologic report (Fig 13). While oblique reformations might permit longer long axis or shorter short centrality measurements than practise the traditional anatomic planes, the challenge of reproducing the same degree of obliquity for serial examinations hinders the generalizability of this method; thus, off-axis oblique reformations are not recommended.

Figure 12: — Effigy 12: A, Transverse, B, coronal, and, C, sagittal reconstruction planes through a pulmonary nodule in the correct lower lobe. The long-axis diameter of the nodule was 16, xiv, and 18 mm in A, B, and C, respectively. Thus, long- and short-axis nodule diameters should exist measured in the sagittal plane in this patient.

Figure 13: — Effigy 13: Transverse CT sections through a complex adenocarcinoma with cystic components in the lingula. Measurement of the solid component is challenging in such cases. *A–C*, The length of the largest substantial solid component is indicated (arrow) in each of three representative sections through the nodule. The morphologic complexity and the fact that the nodule abuts the chest wall make measurements difficult. The walls of cystic components may comprise some solid elements, simply accurate or consequent measurement of such components is oftentimes impossible with manual techniques. Nosotros recommend selecting the largest nodular solid component for measurement, as shown in C. D, Detailed view of the nodule shows placement of the measurement ballast points.

Reconstruction Algorithm and Field of View

The effect of reconstruction algorithm and field of view on the accuracy of lung nodule measurements is controversial. Several published studies failed to evidence a significant effect of either ane on the accuracy of lung nodule measurements (45–47,48), while other studies that did report meaning effects provided alien results, suggesting that either high-spatial-frequency algorithms (49) or low-spatial-frequency algorithms (47) yield the near repeatable results. However, the weight of evidence suggests that for nodules smaller than 10 mm, the reconstruction algorithm does effect measurement accuracy (23,46,48) and that a high-frequency (sharp) algorithm is likely to yield the most authentic measurement results, whereas for nodules larger than ten mm, the choice of reconstruction algorithm has no significant outcome on measurement accurateness.

Display Window Settings

The effect of display window setting on the apparent size of pulmonary nodules is well established, particularly in the instance of subsolid nodules. Almost previous studies investigating the accurateness and variability of lung nodule measurements take been performed by using broad (lung) window settings (window level range, −700 to −500 HU; window width range, 1500–2000 HU). This is because the overall size of subsolid lesions in detail appears artificially smaller when soft-tissue (mediastinal) window settings (window level range, 30–lxx HU; window width range, 350–400 HU) are used because of low-attenuation (ground-glass) components falling below the narrower range of displayed attenuation values (3,13) (Fig xiv). In the past, withal, soft-tissue windows take been systematically practical in combination with lung windows to determine the and then-chosen tumor disappearance charge per unit of part-solid nodules (ie, the ratio betwixt the nodule portion seen on soft-tissue windows and the nodule portion seen on lung windows) (49). Although the tumor disappearance rate has shown promise in optimizing the surgical approach of invasive nodule components (49), the terminology tin can be misleading when referring to the assessment of nodule size by suggesting that a office of the nodule resolves, while in reality it is simply rendered invisible by a technical maneuver. Note that although the window setting does not touch on attenuation measurements, a sharp lung filter can substantially bear on attenuation measurements in unpredictable ways. Thus, only unsharpened images should be used to measure out attenuation.

Figure 14: Transverse CT sections through a nodule (arrow) in the right upper lobe. A, Image obtained with the mediastinal window setting shows just the core of the solid nodule component. B, Image obtained with lung window settings shows the entire solid component and the cystic and ground-glass components of the nodule. Thus, all nodule measurements should exist performed on images obtained with lung window settings.

The electric current literature on nodule measurement with lung and mediastinal display window settings reflects considerable controversy. In a study of 43 patients, the authors (l) constitute that tumor size measured on images obtained with lung windows correlated better with histologic measurements. The same authors also noted that tumor size was a meliorate predictor of advanced disease when measured on mediastinal rather than lung windows. However, split up measurements of the solid component on images obtained with lung windows were not performed. In a report including 52 patients, the authors institute no significant differences between the invasive tumor component and the solid portions, as measured on images obtained with lung and mediastinal windows, respectively (51). In another study including 58 patients, the authors (52) likewise constitute that interobserver agreement was slightly better with mediastinal window settings than with lung window settings. Finally, this aforementioned study plant that measuring the solid component of nodules with lung windows yielded a stronger correlation with histologic show of tumor invasion than when the measurements were performed with mediastinal windows.

Although information technology has been suggested that mediastinal window settings may perform improve than lung window settings when used to assess the size of the solid component (3), there is little information on the comparison of these 2 approaches. Data for minimally invasive adenocarcinomas and small lung adenocarcinomas suggest that lung window measurements may yield results that are closer to pathologic measurements (41,51,52) and that use of mediastinal window settings may result in underestimation of invasive size (51). When interobserver agreement and accuracy were compared with histology in subsolid nodules with a solid component smaller than eight mm, lung window settings had comparable reproducibility only college accurateness than did mediastinal window settings (53). At the present fourth dimension, expert opinion tends to favor use of lung window settings to detect and measure solid components in subsolid nodules. Thus, we recommend utilize of a lung window setting with a high-spatial-frequency (sharp) algorithm for solid component nodule measurements, while we recognize that this deviates from previous recommendations (3) (Fig 15). What appears solid on images obtained with lung window settings and high-spatial-frequency reconstructions should be considered as such (54) (Fig 16).

Figure 15: Transverse CT sections through a pocket-size nodule in the right lower lobe (same nodule every bit in 6, C) reconstructed, A, without and, B, with a loftier-spatial-frequency (abrupt) filter. If all other technical parameters are kept equal, image reconstruction with this filter improves visibility of anatomic detail, notably in the pulmonary nodule (pointer).

Figure 16: — Effigy sixteen: Transverse CT sections of a part-solid nodule in the right lower lobe. A, Both ground-glass and solid components are well defined. B, First, overall nodule dimensions are measured, resulting in an boilerplate bore of 24 mm. C, Then, the long axis of the solid component is measured separately, resulting in a diameter of seven mm.

Radiation Dose and Epitome Noise-reduction Algorithms

Tube current settings are determined by the merchandise-off between a desire to minimize radiations dose and a competing want to maintain image quality. Several studies have concluded that substantial reductions in radiations dose can be achieved without adversely affecting nodule measurement accuracy (5). Nonetheless, the effect of radiation dose on volumetric measurement error has been difficult to establish, with many studies declining to demonstrate a meaning departure between nodule measurements made across a spectrum of exposure levels (48,54–57). Yet, excessive dose reduction affects image quality by degrading nodule boundary definition. The magnitude of these effects volition vary depending on overall trunk habitus and on the size, morphology, and location of the nodule, thereby making generalizable recommendations regarding minimum radiation exposure levels specially challenging; nevertheless, one full general rule for achieving consistent prototype quality is to tailor imaging technique to patient size. The use of iterative reconstruction algorithms can as well affect the accuracy of nodule dimension measurements (vii), peculiarly ground-glass components; however, more information are needed to assess the result of the many variations of iterative reconstruction algorithms currently implemented by various CT manufacturers.

Lung Volume

One study measured both the diameter and the book of lung nodules on CT images caused at total lung capacity and residual volume (55). The researchers plant that both nodule diameter and nodule volume varied nonuniformly from total lung chapters to balance book, with some nodules decreasing in size and other nodules increasing. There was a 16.eight% mean change in accented book beyond all nodules. When stratified by size, the mean of the absolute percentage volume change for nodules larger than 5 mm and that for nodules 5 mm or smaller was non significantly dissimilar (P = .26) (55). Although not acquired at total lung capacity and functional residual capacity, other studies also observed meaning, albeit small, absolute differences in nodule size when measured at different lung volumes (56,57). In do, standardized breathing commands are probable to provide reasonably reproducible lung volumes on serial CT images (58).

Part-Solid Lesions with Several Solid Components

Part-solid lesions with several solid components tin pose a particular claiming, as there currently is no consensus on how the solid components of these lesions should exist measured. One possible approach is to make up one's mind the unmarried largest focus and mensurate it, while reporting but non measuring the remaining foci (Fig 17). An alternative approach was recently used (59) to measure the invasive component of part-solid adenocarcinomas on pathology slides. In this study, the researchers measured all nonlepidic components and expressed their sum every bit a pct of the overall tumor volume, which they multiplied by the full nodule diameter to go far at a linear measurement. Thus, a 25% solid component in a 20-mm nodule would represent to a 5-mm diameter. Although this arroyo has some merit, it has not been used or tested in the context of CT images, it would be time consuming, and information technology would require highly subjective estimates. Currently, the practise in pathology is to measure only the greatest dimension of the largest solid component. Thus, although boosted volumetric or bidimensional measurements accept merit, at a minimum, we recommend measuring the long axis of the largest solid component on images reconstructed with a high-frequency algorithm and displayed on a lung window epitome to enable direct comparison with pathologic measurements. If the consequence is greater than 5 mm, invasion may be considered more likely (54).

Figure 17: Transverse CT sections through a nodule (large arrow) in the left upper lobe at, A, baseline and, B, 3 years later on. Over this fourth dimension, the nodule has developed two solid components (small arrows). In role-solid nodules with multiple solid components, the maximum bore of the largest solid component should be measured. In this nodule, only the larger component was measured (maximum diameter, 5 mm). The smaller solid component did not need to be measured.

Part 3: Directions for Future Enquiry

Maximum Bore or Average of Long- and Brusk-Axis Measurements?

Whereas pathologists express nodule size as the maximum bore, radiologists have transitioned to expressing the size of modest pulmonary nodules as the average of long- and short-centrality measurements. Currently, there is no prove from prospective multicenter studies about the human relationship between these two approaches or about which approach will yield more robust predictive data. In this context, it is important to emphasize that pathologists measure out nodule size primarily for staging (11), whereas radiologists measure nodule size primarily for allocation into risk categories (2). It also must exist emphasized that pathology measurements are not well standardized. Indeed, the previous fourth edition to the TNM supplement states: "Neither in the TNM classification nor in the one^st to 3^rd edition of the TNM supplement are whatsoever statements concerning the way to measure out tumor size for pT classification." According to the American Joint Committee on Cancer Cancer Staging Manual 2009, pT is derived from the bodily measurement of the unfixed tumor in the surgical specimen. It should be noted, however, that up to 30% of shrinkage of soft tissues may occur in the resected specimen. Thus, in cases of discrepancies of clinically and pathologically detected tumor size, the clinical measurement should also be used for pT nomenclature (sixty). This statement underlines not only the lack of standardization of pathology measurement, but also the importance of shut interaction between pathology and radiology with regard to cess of nodule dimensions, given the known limitations of both methods. Although the effect of formalin fixation on the size of modest lung cancers has been investigated (61), in that location is no evidence as to how the corporeality of shrinkage volition affect in vivo CT measurements of a resected nodule. Correlations between CT images and resected lung tumors have been investigated (62), just the series are modest and no information on prognostic implications has been provided. Finally, there is contempo preliminary evidence that the degree of sphericity of small lung tumors is potentially related to result, with less spherical nodules showing improved prognosis (63). This would support undertaking future investigation on potential advantages of providing more than one number for the dimensions of a nodule. Inevitably, these studies will have to exist focused non but on measurement precision and validation, but also on outcomes, to frame the results of technical measurements into a predictive clinical context.

Is Automated Nodule Measurement a Remedy?

Both the advantages and the drawbacks of automatic or semiautomated quantitative lung nodule cess (64) and the uncertainties inherent to using CT as a measurement tool (65) have recently been summarized in the literature. While providing advantages in terms of measurement consistency, more often than not due to less human interaction, the results generated by quantitative nodule cess even so depend on a spectrum of technical factors, including department thickness, reconstruction interval, number of detectors, x-ray beam free energy, application of radiation-reducing exposure variation, and presence or absence of contrast cloth (64). Moreover, it has been shown that the results generated by quantitative nodule assessment yield substantially different results depending on the software package and the CT conquering parameters used (30). Two recent studies investigated the furnishings of dose and reconstruction algorithms on lung nodule measurements (seven,8). One of these studies showed that radiation dose had a meaning event on size, conspicuity, and intralesion pixel distribution when evaluating lung nodules (8). This same study also showed that, when compared with filtered back projection, a model-based iterative reconstruction algorithm had a significant effect on objective measurements of lung nodule size, attenuation, and texture (viii). Moreover, reconstruction of false monochromatic energy levels with dual-energy CT resulted in the measurement of significantly unlike CT numbers (7). This is especially relevant if the utilize of dissimilar dual-energy CT platforms for serial examinations results in changes in measured CT attenuation characteristics that are erroneously attributed to actual changes in tumor attenuation or texture. The implications of these studies are substantial. When i considers the multitude of reconstruction algorithms on the market and the proprietary nature of their technical design, information technology is probable that the so-called black box nature of these algorithms influences lung nodule measurement in ways that are difficult to quantify. These implications apply non only to mere size assessment of nodules, just also to measures of their book and CT characteristics of their internal matrix. Overall, before automated or semiautomated quantitative lung nodule assessment can be more often than not recommended, the factors causing variability between software packages and between CT examinations need to be better understood. Ideally, this meliorate understanding, including understanding the interaction between these factors, would result in a compatible standard for both image reconstruction and paradigm processing, similar to the Digital Imaging and Communications in Medicine standard for the distribution and viewing of medical images. Such a standard could be developed and propagated by the Quantitative Imaging Biomarker Alliance or by other similar organizations. Eventually, result studies will have to prove whether automated or semiautomated quantitative nodule assessment provides advantages that are relevant to patient morbidity and prognosis in addition to interpreter efficiency and measurement reproducibility.

Is Greater Consistency and Quality of Nodule Characterization Achievable?

Recent studies have shown that the categorization of pulmonary nodules is subject to substantial variability, even among experienced thoracic radiologists (66,67). With κ values of 0.619 and 0.670 for label of solid and ground-glass nodules, respectively, interobserver agreement for the categorization of nodules among six experienced thoracic radiologists was not more than "good." Moreover, with a κ value of 0.792, intraobserver agreement too was limited. Finally, correct allocation to either the solid or the subsolid category amidst the six radiologists was accomplished for but 58% (70 of 120) of nodules (66). These findings of moderate inter- and intraobserver agreement have been corroborated subsequently, with κ values of 0.51 and 0.57, respectively, and discordant categorization in 36.4% (1630 of 4480) of nodules where two-thirds of discordant readings (1061 of 1630) would potentially accept inverse nodule management by using management rules relying on nodule classification and size measurements alone (67). Although both studies take potential limitations, they withal address an important problem. Current management recommendations for pulmonary nodules are indeed based on the inherent assumption that nodule categorization is authentic. One decision that could exist drawn from these studies is that radiologists should exist aware of the inherent subjectivity in allocating pulmonary nodules into descriptive categories, such as solid and subsolid. A second conclusion could be that a fundamental reconsideration of current descriptive categories is needed to replace them with more objective descriptors based on quantitative criteria. This would certainly require a essentially college degree of standardization among producers of software packages and manufacturers of CT scanners, as described previously. The upshot, notwithstanding, could be a scale or set of scales of continuous variables characterizing a pulmonary nodule, rather than a limited number of binary descriptive categories. This would potentially let for more accurate and reproducible nodule assessments, notably better reflecting the complex and diverse morphology of nodules currently classified as subsolid.

Decision

Measurement of pulmonary nodules is 1 of the more mutual tasks for radiologists, and this set of recommendations is intended to guide the practical aspects of this chore. It is our intention that these guidelines will assistance standardize the approach to nodule measurements and decrease measurement variability for nodules that may be measured past different radiologists using various CT scanners and conquering protocols. These recommendations too emphasize the potential sources of variability and highlight areas in which further research is needed to better measurement accuracy, consistency, and nodule label. A number of avant-garde semiautomated and automated measurement techniques are currently under investigation, including nodule attenuation, mass assessment, or both; measurements based on attenuation gradients; threshold-based methods; and avant-garde iii-dimensional texture assay. Further research and development in these areas will likely atomic number 82 to more widespread clinical implementation in the future. As with previous guidelines, the electric current guidelines are subject area to changes in the future, as it tin exist expected that the underlying body of knowledge volition evolve. Thus, we recommend that these recommendations be applied with clinical judgment and common sense, and nosotros recognize the importance of other nodule characteristics, such as shape, borders, and limerick, as well as the patients' gamble profile and clinical history.

Disclosures of Conflicts of Interest: A.A.B. Activities related to the present commodity: disclosed no relevant relationships. Activities non related to the present commodity: is a consultant to Spiration and Olympus; received royalties from Elsevier. Other relationships: disclosed no relevant relationships. H.Yard. Activities related to the nowadays article: disclosed no relevant relationships. Activities not related to the present article: institution received a grant from Philips Healthcare, is a consultant for Riverain Technologies, holds stock options in Hologic, and receives patent and licensing fees from UCTech. Other relationships: disclosed no relevant relationships. J.M.Grand. disclosed no relevant relationships. G.D.R. Activities related to the nowadays article: disclosed no relevant relationships. Activities not related to the present commodity: is a board member for GE Healthcare and a consultant for Fovia. Other relationships: disclosed no relevant relationships. C.M.S. Activities related to the present commodity: disclosed no relevant relationships. Activities not related to the present commodity: receives royalties from Elsevier and Thieme. Other relationships: disclosed no relevant relationships. D.P.Due north. disclosed no relevant relationships.

Acquittance

The authors thank Benedikt Heidinger, MD, for back up with the preparation of images.

Author Contributions

Author contributions: Guarantors of integrity of unabridged study, A.A.B., H.Yard.; study concepts/study design or data acquisition or data assay/interpretation, all authors; manuscript drafting or manuscript revision for of import intellectual content, all authors; approving of concluding version of submitted manuscript, all authors; agrees to ensure whatsoever questions related to the work are appropriately resolved, all authors; literature inquiry, A.A.B., H.M., G.D.R., C.M.S., D.P.N.; clinical studies, Grand.D.R.; and manuscript editing, all authors

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Received December 19, 2016; revision requested January 25, 2017; revision received February xiv; accepted March 17; final version accepted March thirty.
Published online: June 26 2017
Published in print: Nov 2017

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Source: https://pubs.rsna.org/doi/full/10.1148/radiol.2017162894