chapter
33
Virtual Microscopy
Katharina Glatz-Krieger
Contents
V irtu a l M ic ro sc o p y
D ia g n o s tic s
V irtu a l S lid e A c q u is itio n
t e le c o n s u lt a t io n
E q u ip m e n t f o r S lid e A c q u is it io n
Q u a lit y A s s u r a n c e
A c q u is it io n S p e e d
n
L
V ir t u a l S lid e Q u a lit y
I
I
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n
1
F o c u s p la n e s
A p p lic a tio n s
T e a c h in g : O n lin e E d u c a tio n
Virtual Microscopy
A v irtu a l m icroscope provides a d ig ital e m u la tio n o f a physi-
cal lig h t m icroscope inc lu d in g fast brow sing th rou g h the slide
to locate an area o f interest, changing the m ag nification, and
id ea lly z o o m in g.1 V irtu a l slides are d ig itized representations o f
histo lo g ic o r cytologic preparations captured as m u ltip le partial
d ig ital images at hig h m ag nification and th en jo in e d to create a
single large image file o r a collection o f m an y files. The h ig h disk
capacities and n e tw o rk b a nd w id th th a t are required fo r the stor-
age and vie w ing o f fu lly d igitized h isto lo g y o r cytology slides
w ith diagnostic q u a lity became available b y the late nineties.
V irtu a l m icroscopy represents one o f m ost recent in n o va tio n s in
the fie ld o f telep atholog y.2 In contrast to tra d itio n a l te le p atho l-
ogy applications, v irtu a l slides m ay be sim ulta ne ou sly accessed
b y m u ltip le users w h o can access and in d iv id u a lly m anip ulate
the same slide at the same tim e over the W o rld W id e Web. In
a d d itio n, v irtu a l m icroscopy enables novel applications in edu-
cation, diagnostics, and research.
Virtual Slide Acquisition
Equipment for Slide Acquisition
A v irtu a l m icroscopy system consists o f three com p onents.1
1. V irtu a l slid e a c q u is itio n system (V SA S): d ig itiz a tio n o f
th e slid e and p rocessing o f th e im age data.
2 . Server: data m a n a g e m e n t.
3. C lie n t: slid e vie w in g .
Slides m ay be d ig itized b y grabbing single images (im age
tilin g ), o r b y lin e scanning,3 o r by m in ia tu riz e d m icroscope
arrays.4 Special alg orithm s are needed fo r seamless a lig nm en t
o f the im age tiles/stripes and fo r focusing. M eanw hile, various
com m ercial scanning systems are o n the m arket th a t use one o f
the three d ig itiz a tio n techniques m en tio n ed above.5,6
Large storage systems are needed fo r data storage and slide
p rovisioning . C u rren t generation personal com puters are suited
fo r data processing and image view ing.
V arious com m ercial and self-m ade c lien t interfaces exist
fo r desktop vie w ing o r W eb browser-based vie w ing o f v irtu a l
slides.5-8 M ost vendors o f VSASs o ffe r th e ir ow n slide-view ing
softw are w ith varying ease o f slide navigating and zoom ing .
D esktop vie w ing softw are th a t has to be installed o n the client
com p uter generally provides m ore features b u t hig h er com plex-
ity. O n the o th e r hand, W eb browser-based viewers th a t enable
the user to v ie w the slide over the In te rn e t often do n o t require
in s ta lla tio n o f softw are b u t u su a lly o ffe r few er features. The c li-
ent u su a lly shows a th u m b n a il v ie w o f the entire specim en w ith
a fram e ind icating the p o sitio n and size o f the clipping seen
in the m a in im age area. A n y region o f the v irtu a l slide m ay be
in s ta n tly view ed b y clicking o n a new p o sitio n in the overview
image, dragging the m a in image, o r dragging the fram e in the
th u m b n a il overview. Furtherm ore, the user can choose fro m
various m agnifications. Som e systems also o ffe r a stepless in
and o u t z o o m in g o p tio n.8 Special data transfer protocols a llo w
p a rtitio n in g o f the im age data sent fro m the server to the c li-
ent (user). T he server transfers o n ly the fra ctio n o f the slide th a t
the user observes on his o r h er screen at a given m om en t. In
a d d itio n, the c lien t prefetches neig hb oring parts o f the slide to
a llo w fo r faster panning. Those regions o f the slide th a t have
already been view ed b y the user are cached and id e a lly available
im m e d ia te ly fo r review ing.
Acquisition Speed
O ne obvious and central weakness o f m ost existing VSASs is
slow acq uisition speed. As lo n g as the system is planned to serve
o n ly educational purposes,6 th is shortcom ing m ay be accept-
able. However, i f v irtu a l slides are to be introd uced in ro u tin e
diagnostics, a very fast and autom ated system — m o s tly at a
hig h er price— is m and atory.4,9,10 T he th ro u g h p u t capacity fo r
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