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Ebook Observer performance methods for diagnostic imaging: Part 2

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Nội dung chi tiết: Ebook Observer performance methods for diagnostic imaging: Part 2

Ebook Observer performance methods for diagnostic imaging: Part 2

PartThe free-response ROC(FROC) paradigmKH

Ebook Observer performance methods for diagnostic imaging: Part 2l now focus has been on the receiver operating characteristic (ROC) paradigm. For diffuse interstitial lung disease,* and diseases like it, where dise

ase location is implicit (by definition diffuse interstitial lung disease is spread through and confined to lung tissues) this is an appropriate parad Ebook Observer performance methods for diagnostic imaging: Part 2

igm in the sense that possibly essential information is not being lost by limiting the radiologist s response in the ROC study to a single rating. Ihe

Ebook Observer performance methods for diagnostic imaging: Part 2

extent of the disease, that is, how far it has spread within the lungs, is an example of essential information that is still lost.1 Anytime essential

PartThe free-response ROC(FROC) paradigmKH

Ebook Observer performance methods for diagnostic imaging: Part 2by modifying it to account for extent of disease. However, this is not the direction taken in this book. Instead, the direction taken is accounting fo

r location of disease.In clinical practice it is not only important to identify whether the patient is diseased, but also to offer further guidance to Ebook Observer performance methods for diagnostic imaging: Part 2

subsequent care givers regarding other characteristics (such as location, size, extent) of the disease. In most clinical tasks if the radiologist bel

Ebook Observer performance methods for diagnostic imaging: Part 2

ieves the patient may be diseased, there is a location (or more than one location) associated with the manifestation of the suspected disease. Physici

PartThe free-response ROC(FROC) paradigmKH

Ebook Observer performance methods for diagnostic imaging: Part 2e collected information to a single rating representing the confidence level that there is disease somewhere in the patient’s imaged anatomy. The emph

asis on somewhere is because it begs the question: if the radiologist believes the disease is somewhere, why not have them to point to it? In fact, th Ebook Observer performance methods for diagnostic imaging: Part 2

ey do point to it in the sense that they record the location(s) of suspect regions in their clinical report, but the ROC paradigm cannot use this info

Ebook Observer performance methods for diagnostic imaging: Part 2

rmation. Neglect of location information leads to loss of statistical power as compared Io paradigms that account for location information. One way of

PartThe free-response ROC(FROC) paradigmKH

Ebook Observer performance methods for diagnostic imaging: Part 2s subjecting more patients to imaging procedures2• Diffuse interstitial lung disease refers to disease within both lungs that affects the interstitium

or connective tissue that forms the support structure of the lungs' air sacs or alveoli. When one inhales, the alveoli fill with air and pass oxygen Ebook Observer performance methods for diagnostic imaging: Part 2

to the blood stream. When one exhales, carbon dioxide passes from the blood into the alveoli and is expelled from the body. When interstitial disease

Ebook Observer performance methods for diagnostic imaging: Part 2

is present, the interstilium becomes inflamed and stiff, preventing the alveoli from fully expanding. this limits both the delivery of oxygen to the b

PartThe free-response ROC(FROC) paradigmKH

Ebook Observer performance methods for diagnostic imaging: Part 2eoli, which further hampers lung function.259260 The FROC paradigmand not using the optimal paradigm/analysis. This is the practical reason for accoun

ting for location information in the analysis. The scientific reason is that including location information yields a wealth of insight into what is li Ebook Observer performance methods for diagnostic imaging: Part 2

miting performance; these are discussed in Chapter 16 and Chapter 19. This knowledge could have significant implications—currently widely unrecognized

Ebook Observer performance methods for diagnostic imaging: Part 2

and unrealized—for how radiologists and algorithmic observers are designed, trained and evaluated. There are other scientific reasons for accounting

PartThe free-response ROC(FROC) paradigmKH

Ebook Observer performance methods for diagnostic imaging: Part 2one exception,4 much of the observer performance experts have yet to grasp it.This part of the book, the subject of which has been the author’s prime

research interest over the past three decades, starts with an overview of the FROC paradigm introduced briefly in Chapter 1. Practical details regardi Ebook Observer performance methods for diagnostic imaging: Part 2

ng how to conduct and analyze an FROC study are deferred to Chapter 18. The following is an outline of this chapter. Four observer performance paradig

Ebook Observer performance methods for diagnostic imaging: Part 2

ms are compared using a visual schematic as to the kinds of information collected. An essential characteristic of the FROC paradigm, namely search, is

PartThe free-response ROC(FROC) paradigmKH

Ebook Observer performance methods for diagnostic imaging: Part 2ed. Key differences between FROC and ROC data are noted. The FROC plot is introduced and illustrated with R examples. The dependence of population and

empirical FROC plots on perceptual signal-to-noise ratio (pSNR) is shown. The expected dependence of the FROC curve on pSNR is illustrated with a sol Ebook Observer performance methods for diagnostic imaging: Part 2

ar analogy— understanding this is key to obtaining a good intuitive feel for this paradigm. Hie finite extent of the FROC curve, characterized by an e

Ebook Observer performance methods for diagnostic imaging: Part 2

nd-point, is emphasized. Two sources of radiologist expertise in a search task are identified: search and lesion-classification expertise, and it is s

PartThe free-response ROC(FROC) paradigmKH

Ebook Observer performance methods for diagnostic imaging: Part 2ion specific paradigmsLocation-specific paradigms take into account, to varying degrees, information regarding the locations of perceived lesions, so

they are sometimes referred to as lesion-specific (or lesionlevel5) paradigms. Usage of this term is discouraged. In this book, the term lesion is res Ebook Observer performance methods for diagnostic imaging: Part 2

erved for true malignant* lesions* (distinct from perceived lesions or suspicious regions that may not be true lesions).All observer performance metho

Ebook Observer performance methods for diagnostic imaging: Part 2

ds involve detecting the presence of true lesions. So, ROC methodology is, in this sense, also lesion-specific. On the other hand, location is a chara

PartThe free-response ROC(FROC) paradigmKH

Ebook Observer performance methods for diagnostic imaging: Part 2e three location-spedtie paradigms: the free-response ROC (FROC),6'7-" the location ROC (LROC),’2-16 and the region of interest (ROI).17-18* Benign le

sions are simply normal tissue variants that resemble a malignancy, but are not malignant.’ Lesion: a region in an organ or tissue that has suffered d Ebook Observer performance methods for diagnostic imaging: Part 2

amage through injury or disease, such as a wound, ulcer, abscess, tumor, and so on.12.2 Location . r......._Figure 12.1 shows a mammogram as it might

Ebook Observer performance methods for diagnostic imaging: Part 2

be interpreted according to current paradigms—these are not actual interpretations, just schematics to illustrate essential differences between the p

PartThe free-response ROC(FROC) paradigmKH

Ebook Observer performance methods for diagnostic imaging: Part 2rceived lesions or suspicious regions. From now on, for brevity, the author will use the term suspicious region.The numbers and locations of suspiciou

s regions depend on the case and the observer’s skill level. Some images are so obviously non-diseased that the radiologist sees nothing suspicious in Ebook Observer performance methods for diagnostic imaging: Part 2

them, or they are so obviously diseased that the suspicious regions are conspicuous. Then there is the gray area where one radiologist’s suspicious r

Ebook Observer performance methods for diagnostic imaging: Part 2

egion may not correspond to another radiologist s suspicious region.In Figure 12.1, evidently the radiologist found one of the lesions (the lightly sh

PartThe free-response ROC(FROC) paradigmKH

Ebook Observer performance methods for diagnostic imaging: Part 2ghtly shaded crosses that are relatively far from the true lesions). To repeat, the term lesion is always a true or real lesion. The prefix true or re

al is implicit. The term suspicious region is reserved for any region that, as far as the observer is concerned, has lesion-like characteristics, but Ebook Observer performance methods for diagnostic imaging: Part 2

may not be a true lesion.1In the ROC paradigm. Figure 12.1 (top left), the radiologist assigns a single rating indicating the confidence level that th

Ebook Observer performance methods for diagnostic imaging: Part 2

ere is at least one lesion somewhere in the image.* Assuming a 1 through 5 positive directed integer rating scale, if the left-most lightly shaded cro

PartThe free-response ROC(FROC) paradigmKH

Ebook Observer performance methods for diagnostic imaging: Part 2ight), the dark shaded crosses indicate suspicious regions that were marked or reported in the clinical report, and the adjacent numbers are the corre

sponding ratings, which apply to specific regions in the image, unlike ROC, where the rating applies to the whole image. Assuming the allowed positive Ebook Observer performance methods for diagnostic imaging: Part 2

-directed FROC ratings are 1 through 4, two marks are shown, one rated FROC-4, which is close to a true lesion, and the other rated FROC-1, which is n

Ebook Observer performance methods for diagnostic imaging: Part 2

ot close to any true lesion. The third suspicious region, indicated by the lightly shaded cross, was not marked, implying its confidence level did not