IMAGING SCIENCE AND and common form of

INFORMATICS (2) radiography is x-ray. For this

imaging procedure, an x-ray
machine beams high-energy
With modern technology in the waves onto the body. The soft
medical field, doctors are able to tissues, like organs and skin,
diagnose and treat patients without do not absorb these waves,
any dangerous side effects. Medical whereas hard tissues like
imaging is considered to be one of bones do absorb such waves.
the best means to achieve that aim, The machine transfers the x-
being able to observe what’s ray results onto a film,
happening inside the body without indicating the body parts that
the requirement for surgery or other absorbed the waves in white
invasive measures. Medical imaging and leaving the unabsorbed
can be defined as a technique of material in black.
developing visual representations of 2. Ultrasound: This imaging
areas inside the human body to procedure makes use of high-
diagnose health issues and frequency sound waves, that
accordingly monitor treatment. The is reflected off tissue to
procedure has had a great impact on develop images of joints,
public health. Being one of the most muscles, organs, and soft
powerful resources available for the tissues. It’s like shining light
patients, medical imaging can be on the inside of the body,
used for both therapeutic and except that the light travels
diagnostic purposes. through the skin layers and
can only be viewed using
electronic sensors. Being one
Types of medical imaging of the most cost-effective
There are numerous kinds of forms of medical imaging,
medical imaging, and more means Ultrasound has no harmful
are being developed as technology effects and is also regarded as
advances. All kinds operate the safest form of medical
diversely to develop images of imaging with a wide range of
what’s occurring inside the body. applications.
3. Magnetic Resonance
1. Radiography: This imaging Imaging: This particular
procedure uses imaging procedure involves
electromagnetic radiation to magnetic fields and radio
take images of the inside of waves to look at the organs
the body. The most popular and other structures in the
 human body. The process prevents the requirement for
needs an MRI scanner, which exploratory surgery.
is a huge tube that contains a 5. Fluoroscopy: a study of
massive circular magnet. This moving body structures--
magnet creates a magnetic similar to an X-ray "movie." A
field that aligns the protons of continuous X-ray beam is
hydrogen atoms in the body. passed through the body part
The protons are then exposed being examined. The beam is
to radio waves, causing the transmitted to a TV-like
protons to rotate. When the monitor so that the body part
radio waves are turned off, the and its motion can be seen in
protons relax and realign detail.
themselves, emitting radio 6. C-Arm: mobile imaging unit
waves in the recovery process used primarily
that can be sensed by the for fluoroscopic imaging
machine to develop an image. during surgical and orthopedic
4. Computer Tomography procedures. It also consists of
(CT): These are a form of X- a computer workstation used
ray that develops 3D pictures to view, manipulate, store and
for diagnosis. Also known as transfer the images.
Computed Axial Tomography
Medical Image Digitalization and
(CAT), it uses X-rays to
Acquisition Gateway
develop cross-sectional
images of the human body. INTEGRATION WITH
The scanner has a huge PICTURE ARCHIVING AND
circular opening for the COMMUNICATION SYSTEMS
patient to lie on a motorized (PACS)
table. The detector and X-ray Image acquisition is the first point of
then rotate around the patient data entry into a PACS, and as such,
developing a narrow ‘fan- errors generated here can propagate
shaped’ beam of x-rays that throughout the system, adversely
passes through a section of the affecting clinical operations. General
patient’s body to develop an predictors for successful
image. CT scans offer greater incorporation of image acquisition
clarity than conventional x- devices into a digital imaging
rays with more precise images department include ease of device
of the bones, blood vessels, integration into the established daily
internal organs, and soft tissue workflow routine of the clinical
within the body. In most environment, high reliability and
cases, the use of CT scans
fault tolerance of the device, In 1994, at the Radiological Society
simplicity and intuitiveness of the of North America (RSNA) Meeting,
user interface, and device speed. a variety of imaging vendors
participated in an impressive
DIGITAL IMAGING AND
demonstration of the new and
COMMUNICATIONS IN
evolving imaging standard (ACR-
MEDICINE (DICOM) consists of
NEMA 3.0) or what is currently
a standard image format as well as a
known as the DICOM standard.
network communications protocol.
Participants attached their devices to
Compliance with this standard
a common network and transmitted
enables an open architecture for
their images to one another. In
imaging systems, bridging hardware
addition to the standard image
and software entities and allowing
format of ACR-NEMA 2.0, the
interoperability for the transfer of
DICOM standard included a
medical images and associated
network communications protocol,
information between disparate
or a common language for sending
systems.
and receiving images and relevant
The push by the radiological data over a network.
community for a standard format
The DICOM standard is used, for
across imaging devices of different
example, to negotiate a transaction
models and makes began in 1982.
between a compliant imaging
Collaboration between the American
modality and a compliant PACS
College of Radiology (ACR) and the
workstation. The scanner notifies the
National Electrical Manufacturers
workstation, in a language both
Association (NEMA) produced a
understand, that it has an image
standard format (ACR-NEMA 2.0)
study to send to it. The workstation
with which to store an image
replies to the modality when it is
digitally. It consisted of a file header
ready to receive the data. The data is
followed by the image data. The file
sent in a format known to all, the
header contained information
workstation acknowledges receipt of
relevant to the image, such as matrix
the image, and then the devices end
size or number of rows and columns,
their negotiation.
pixel size, and grayscale bit depth,
as well as information about the Most of the major manufacturers of
imaging device and technique, (e.g., imaging devices currently comply
Brand X CT scanner, acquired with with the DICOM standard, thus
contrast). Patient demographic data greatly facilitating an open systems
such as name, date of birth, and so architecture consisting of
on, were also included in the image multivendor devices. For many
header. legacy devices purchased prior to
the establishment of DICOM, an Health Level Seven (HL7) is the
upgrade path to compliance can be RIS-HIS standard, and compliance
performed. For those few devices with it is desirable. RIS-HIS
that do not yet meet the standard, databases are typically patient-
interface boxes consisting of centric, enabling query and retrieval
hardware equipment and software of information by the patient, study,
programs that convert the image series, or image data hierarchy.
data from the manufacturer’s Integration of RIS-HIS data with the
proprietary format to the standard PACS adds intelligence to the
form are available. system, helping to move data around
the system based on “how and what
RADIOLOGY INFORMATION
data should be delivered where and
SYSTEM (RIS) –HOSPITAL
when,” automating the functions
INFORMATION SYSTEM (HIS)
performed traditionally by the film
INTERFACING FOR DATA
librarian.
VERIFICATION
SQL- Standard Query Language. It
Equally essential, particularly at
acquisition, is integrating the RIS
and/or HIS with the PACS. This
greatly facilitates input of patient
demographics (name, date, time,
medical record number [MRN] to
uniquely identify a patient,
accession number [AccNum] to
uniquely identify an imaging
examination, exam type, imaging
parameters, etc.), and enables
automatic PACS data verification,
correlation, and error correction with
the data recorded in the RIS-HIS.
Most imaging modalities are now
tightly coupled with the RIS, is used to query, update and delete
providing automatic downloading of data from data base.
demographic information from the HL7 stands for Health Level Seven
RIS via barcode readers or directly International (HL7), which is a not-
to the scanner console (via modality for-profit, ANSI-accredited
worklist capability) and hence to the standards developing organization
DICOM header. This eliminates the dedicated to providing a
highly error-prone manual entry of comprehensive framework and
data at acquisition. related standards for the exchange,
integration, sharing and retrieval of and levels. Direct capture of the
electronic health information that digital data will allow the viewer to
supports clinical practice and the dynamically window and level
management of health service through each of these settings on the
delivery. HL7 provides a framework fly (in real time) at the softcopy
that helps govern how electronic display station. Whereas, to view all
health information is retrieved, appropriate window and level
shared, exchanged and integrated. settings on film, several copies of
the study would have to be printed,
ACQUISITION OF THE
one at each window and level
NATIVE DIGITAL CROSS-
setting. If one performs the analog
SECTIONAL MODALITIES
acquisition or frame grabbing of the
Image acquisition from the digital data, the viewer can only
inherently digital modalities such as window and level through the 8 bits
CT, MRI, and US should be a direct captured, which may not be
digital DICOM capture. Direct sufficient. Thus, direct capture of
digital interfaces allow capture and digital data from the inherently
transmission of image data from the digital modalities is the preferred
modality at the full spatial resolution method of acquisition. Table 11.1
and full bit depth of grayscale lists the cross-sectional modalities
inherent to the modality, while commonly interfaced to PACS along
analog (video) frame grabbers with their inherent file sizes and bit
digitize the video signal voltage
output going to an image display,
such as a scanner console monitor.
In the framegrabbing method, as in
printing an image to film, the image
quality is limited by the process to
just 8 bits (or 256 gray values) while
most modalities have the capability
to acquire in 12, 16, or even 32 bits
for color data. Capture of only 8 bits
may not allow viewing in all the
appropriate clinical windows and
levels or contrast and brightness depths.
settings and is therefore not optimal.
For example, when viewing a CT of ACQUISITION OF
the chest, one may wish to view in PROJECTION RADIOGRAPHY
lung window and level settings and Methods for digital image
in mediastinal and bone windows acquisition of the conventional
projection x-ray include via CR infrequently used in PACS due to
scanners (imaging with their high cost.
photostimulable or storage
More commonly used are film
phosphors), digitization of existing
scanners such as the CCD and laser
analog film, and DR devices. Digital
scanners, sometimes called flatbed
acquisition of images already on
scanners. CCD scanners utilize a
film can be accomplished using a
row of photocells and uniform bright
variety of image digitization devices
light illumination to capture the
or film scanners.
image. A lens focuses the
FILM DIGITIZER transmitted light from the
collimated, diffuse light source onto
Film digitizers will still be necessary
a linear CCD detector, and the signal
even in the all-digital or filmless
is collected and converted to a
imaging department, so that film
digital electronic signal via an ADC
images from outside referrals
converter. CCD scanners have a
lacking digital capabilities can be
maximum resolution of 4096 x 4096
acquired into the system and viewed
x 8 to 12 bits, but have a narrow film
digitally. Film digitizers convert the
optical density range to which they
continuous optical density values on
can respond. CCD scanners have
film into a digital image by
been used in high-end teleradiology
sampling at discrete evenly spaced
or entry-level in-house film
locations and quantizing the
distribution systems, such as image
transmitted light from a scan of the
transmission to the intensive care
film into digital numbers. Several
units (ICUs).
types of film digitizers exist today,
with some used more frequently The laser scanner or laser film
than others in PACS and digitizer uses either a helium-neon
teleradiology applications. (HeNe) gas laser or a solid-state
diode laser source. The laser beam is
it has a maximum resolution of 1024
focused by lenses and directed by
x 1024 x 8 bits (256 grays), thus
mirror deflection components, and
limiting the range of window and
the light transmitted through the film
level, or contrast and brightness
is collected by a light guide, its
values the resulting digital image
intensity detected by a
can be displayed in. Digital cameras
photomultiplier tube, converted to a
produce a digital signal output
proportional electronic signal, and
directly from the camera at a
digitized in an ADC. Laser scanners
maximum resolution of 2048 x 2048
use a fine laser beam of generally
x 12 bits (4096 grays) but are still
variable or adjustable spot sizes
down to 50 microns (producing an
image sharpness of approximately x-ray image. Like the conventional
10-line pairs per millimeter intensifying screen, CR plates
[lp/mm]). They have a maximum produce light in response to x-rays at
spatial resolution of 4096 x 5120 the time of exposure. However,
and a grayscale resolution of 12 bits storage phosphor plates have the
and can accommodate the full additional property of being capable
optical density range of film. They of storing some of the absorbed x-
are semi- or fully automatic in ray energy as a latent image. Plates
operation and are currently the are typically made of a europium-
scanner of choice for PACS doped barium fluoro-halide-halide
applications even though they are crystallized matrix. Electrons from
often more expensive than CCD the dopant ion become trapped just
scanners. below the conduction band when
exposed to x-rays. Irradiating the IP
at some time after the x-ray
COMPUTED RADIOGRAPHY exposure with red or nearinfrared
Computed radiography refers to laser light liberates the electrons into
projection x-ray imaging using the conduction band, stimulating the
photostimulable or storage phosphor to release some of its
phosphors as the detector. In this stored energy in the form of green,
modality, x-rays incident upon a blue, or ultraviolet light, the
photostimulable phosphor (PSP)- phenomenon of photostimulable
based image sensor or imaging plate luminescence. The intensity of light
(IP) produce a latent image that is emitted is proportional to the
stored in the IP until stimulated to amount of x-ray energy absorbed by
luminesce by laser light. This the storage phosphor. The readout
released light energy can be process uses a precision laser spot
captured and converted to a digital scanning mechanism in which the
electronic signal for transmission of laser beam traverses the IP surface
images to display and archival in a raster pattern. The stimulated
devices. light emitted from the IP is collected
and converted into an electrical
A CR system consists of a screen or signal, with optics coupled to a
plate of a stimulable phosphor photomultiplier tube (PMT). The
material that is usually contained in PMT converts the collected light
a cassette and is exposed in a from the IP into an electrical signal,
manner similar to the traditional which is then amplified, sampled to
screen-film cassette. The PSP in the produce discrete pixels of the digital
IP absorbs x-rays that have passed image, and sent through an ADC to
through the patient, “recording” the quantize the value of each pixel (i.e.,
a value between 0 and 1023 for a 10- In addition to CR devices for digital
bit ADC or between 0 and 4095 for a image acquisition of projection x-

12-bit ADC). Not all of the stored rays, there are the maturing direct
energy in the IP is released during digital detectors falling under the
the readout process. Thus, to prepare general heading of digital
the IP for a new exposure, the IP is radiography (DR). Unlike
briefly flooded with high-intensity conventional screen-film
(typically fluorescent) light. This radiography in which the film
erasure step ensures removal of any functions as the imaging sensor, or
residual latent image. recording medium, as well as the
display and storage media, DR, like
CR, eliminates film from the image-
DIGITAL RADIOGRAPHY recording step, resulting in a
separation of image capture from
image display and image storage.
This separation of functions
potentiates optimization of each of
these steps individually. In addition,
DR, like CR, can capitalize on
features common to digital or
filmless imaging, namely, the ability
to acquire, transmit, display,
manipulate, and archive data
electronically, overcoming some of
the limitations of conventional
screen film radiography. Digital
imaging benefits include remote
access to images and clinical “DR” may be used by some to refer
information by multiple users to direct radiography, also called
simultaneously, permanent storage direct digital radiography (DDR), as
and subsequent retrieval of image the subset of digital radiography in
data, expedient information delivery which x-ray absorption within the
to those who need it, and efficient, detector is converted into a
cost-effective workflow with proportional electric charge without
elimination of film. In this chapter, an intermediate light conversion
DR refers to devices in which the step.

digitization of the x-ray signal

takes place within the detector
itself, providing an immediate full-
fidelity image on a softcopy
display monitor. Compare this with
CR, which utilizes a PSP IP detector
in a cassette design that must be
processed in a CR reader following
x-ray exposure, for conversion to a
digital image. Digital radiography
devices may be classified as direct
or indirect based on their detector
design and conversion of absorbed
x-rays into an image. The acronym
INDIRECT VERSUS DIRECT transistor (FET) switch that allows
CONVERSION DR refers to the active readout of the charge
devices for direct digital acquisition stored in the capacitor. Arrays of
of projection radiographs in which individual detector areas are
the digitization of the x-ray signal addressed by orthogonally arranged
takes place within the detector. gate switches and data lines to read
Digital radiography devices, also the signal generated by the
called flat-panel detectors, include absorption of x-rays in the detector.
two types, indirect conversion The TFT arrays are used in
devices in which light is first conjunction with a direct x-ray
generated using a scintillator or photoconductor layer or an indirect
phosphor and then detected by a x-raysensitive phosphor-coated
CCD or a thin-film-transistor (TFT) light-sensitive detector or
array in conjunction with photodiode array. An example DDR
photodiodes; and DDR devices, device, diagrammed in cross section
which consist of a top electrode, in Figure 11.9, uses a multilayer
dielectric layer, selenium x-ray detector in a cassette design, in
photoconductor, and thin-film pixel which the x-ray energy is converted
array. Figure 11.8 shows a directly to electron-hole pairs in an
comparison of the direct and indirect amorphous selenium (Se)
energy conversion steps in the photoconductive conversion layer.

production of a digital x-ray image. Charge pairs are separated in a bias

DDR devices offer direct energy field such that the holes are collected
conversion of x-ray for immediate in the storage capacitors and the
readout without the intermediate electrons drift toward the Se-
light conversion step. The basis of dielectric interface. At the end of
DR devices is the large area TFT exposure, the image resides in the
active matrix array, or flat panel, in pixel matrix in the form of charges,
which each pixel consists of a signal with the charge proportional to the
collection area or charge collection absorbed radiation. At the end of
electrode, a storage capacitor, and an readout, the charges are erased to
amorphous silicon fieldeffect prepare for another detection cycle.
An example indirect DR device uses
an x-ray-sensitive phosphor coating
on top of a light-sensitive flat panel
amorphous silicon (Am-Si) detector
TFT array. The x-rays are first
converted to light and then to a
proportional charge in the
photodiode (typically a cesium
iodide [CsI] scintillator), which is
then stored in the TFT array where
the image signal is recorded.

End Day 2…