Rapid progress in digital X�ray engineering suggests

that the era of conventional techniques of medical diag�

nosis service and X�ray diagnosis in general will end in the

foreseeable future, being replaced by filmless technology.

A number of problems should be solved to implement this

technology. The goal of this work was to briefly describe

these problems.

1. New Role of X�Ray Equipment in the System of MedicalDiagnosis

In recent years, the installed contingent of medical

X�ray equipment has undergone considerable change

according to the general trends in development of X�ray

diagnosis apparatuses. In addition to the general trend of

transition to digital imaging (typical of radiation diagno�

sis in general), there is a recent trend toward specific

applications of medical diagnosis.

In industrially developed countries, the following

changes in medical technologies are occurring:

– extension of the area of application of ultrasonic

diagnosis (USD) (3�D� and 4�D�imaging, color Doppler

mapping, color US angiography, USD breast examina�

tion in female patients);

– extension of the area of application of X�ray com�

puter tomography (XCT) determined by progress in spiral

multidetector systems for 3�D X�ray imaging within frac�

tions of millisecond;

– extension of the area of application of magnetic

resonance imaging (MRI) based on the capabilities of

modern software and microprocessors, MR angiography,

MR contrasting with gadolinium compounds, and static

magnets of MR tomographs.

The technology of radionuclide diagnosis changed

the least. Presently, all gamma chamber models provide

emission tomography. Double positron–electron emission

tomography (PET) provides fundamentally new prospects

in medical diagnosis. This technology provides high spa�

tial resolution, but it requires new radionuclide chemical

materials with gamma�quantum energy 1024 keV.

Virtually all types of X�ray diagnosis are character�

ized by decrease in the area of application of both film

and digital imaging technologies.

1. X�Ray examination of the gastrointestinal tract

(GIT): in recent years, there has been a significant

decrease in the number of X�ray examinations of the GIT

in favor of endoscopy, virtual endoscopy, XCT, and USD

of kidney, liver, and pancreas.

2. Chest X�ray: conventional prophylactic

roentgenography is gradually being replaced by panoram�

ic XCT of lungs, whereas diagnostic 3�D X�ray computer

tomography is gradually being replaced by XST.

3. Roentgenography of bone–joint systems: MRI

methods are widely used for roentgenography of bone–

joint system diseases. The diagnostic capabilities of MRI

in diagnosis of soft tissues around bone injury or patholo�

gy are greater than those of conventional X�ray imaging

methods.

4. Studies of the cardiovascular system: X�ray

angiography is being replaced by ultrasonic scanning,

XCT, and MR�angiography.

5. X�Ray monitoring in surgery: X�ray and US mon�

itoring in surgery is being actively developed. This is par�

ticularly true in the case of intravascular surgery.

Multipurpose mobile C�arc X�ray diagnostic apparatuses

are extensively used.

6. Mammography: X�ray mammography is domi�

nant. However, methods of electromagnetic and US

mammography are being introduced.

7. Dental X�ray: dental X�ray is the only area of con�

ventional radiology that still has its significance. Only a

Biomedical Engineering, Vol. 40, No. 5, 2006, pp. 215�218. Translated from Meditsinskaya Tekhnika, Vol. 40, No. 5, 2006, pp. 3�6.

Original article submitted March 30, 2006.

2150006�3398/06/4005�0215 2006 Springer Science+Business Media, Inc.

All�Russian Scientific�Research Institute for Medical Instrument

Engineering, Moscow. Elektron Scientific�Manufacturing Association,

St. Petersburg, Russia.

Prospects for the Future

N. N. Blinov and A. I. Mazurov

Research, Design, and Technology

216 Blinov and Mazurov

few methods of XCT and MRI are used in maxillofacial

diagnosis.

There is a 1�2% increase in the total number of X�ray

examinations and radiation load on the population world�

wide. The use of a given X�ray method is determined by its

diagnostic capacity. Some methods (CT, MRI, radionu�

clide diagnosis) can be applied to any organ of the human

body [1]. However, these methods are rather expensive.

Therefore, roentgenography occupies the leading place.

The distribution of X�ray diagnostic methods in 2002

according to Fuji Medical System [2] is shown in Fig. 1.

Roentgenography should be transitioned to digital

technologies. However, digital technologies require a

number of problems to be solved.

2. The Main Problem of Introduction of DigitalTechnologies

In our opinion, development of the theoretical basis

of digital engineering is the main problem, because the

theoretical basis of analog engineering should be updated

[7]. This concerns both image perception and image for�

mation systems. In addition, fundamentally new areas of

X�ray engineering have appeared: digital detectors, digital

videoprocessors, systems for digital image transmission

and storage (PACS), radiological and information sys�

tems (RIS), hospital information systems (HIS), and tel�

evision radiology. Unified information approach to digi�

tal X�ray systems should take into account all compo�

nents of digital X�ray systems.

This problem cannot be solved without development

of a unified system of terms, methods, and testing meth�

ods of the new generation of devices. Work for develop�

ment of such a system has been performed for at least ten

years both nationwide and worldwide. There are recom�

mendations of IEC and GOST R of Technical Committee

TK 411 “Apparatuses and Equipment for X�Ray

Diagnosis, Therapy, and Dosimetry Gosstandart RF

(VNIIIMT)”. This work should be continued until a

complete unified system of characteristics of digital

images, methods, and testing systems is developed.

Coupling of shadow image parameters with informa�

tion characteristics of digital image is also very important.

In the previous century film–X�ray systems failed to solve

this problem. Particularly, this concerns image contrast,

resolution, and dynamic range.

The sensitivity of X�ray kits with resolution 5�

10 mm–1 does not allow low�power and sharp�focus X�ray

tubes to be used at focal spot diameter <0.6 mm.

Therefore, the ability of detector to resolve fine details is

better than the input X�ray image. As a result, the resolu�

tion of an X�ray apparatus at object size 1.2 mm (deeply

located organs: lungs, heart, GIT) is limited by geometri�

cal unsharpness. The resolution of an X�ray apparatus at

this object size is lower than the resolution of the X�ray

detector [8]. The dynamic range of the X�ray kits (20�30)

does not allow the contrast of shadow images of organs

(more than ×100) to be represented.

There are no fundamental limitations on the solution

of this problem in digital X�ray apparatuses. Even in cur�

rently available digital X�ray apparatuses, the problem of

dynamic range has been solved. The problem of microfo�

cal roentgenography should be solved to implement

detector resolution in full measure and detail resolution

better than that in the detector (reduce focal size of X�ray

tube and increase maximal load on focus).

Information theory should be used to describe X�ray

image formation and visualization. This theory uncovers

the inconsistency between shadow image parameters

(details, mobility, contrast) and detector parameters (spa�

tiotemporal resolution and dynamic range). This would

make it possible to find consistency between image detail

and spatial resolution of detector; image contrast and

dynamic range; mobility and temporal resolution. Let us

consider the following example. As noted above, the res�

olution of an X�ray apparatus at object size 1.2 mm is lim�

ited by geometrical unsharpness. The dynamic range of

the X�ray kits does not allow the contrast of the shadow

images to be represented.

3. The Problem of Dose Reduction during X�RayExamination

The reduction of radiation load is very important. In

analog systems, radiation dose is determined by required

CT, 8%Roentgenography,

70%Roentgenoscopy,

3%

Ultrasonicscanning,

11%

MRI, 6%

Nuclearmedicine,

3%

Fig. 1. Frequency of use of X�ray diagnostic methods (2001).

Prospects for the Future 217

film darkening (D = 1�1.5). In digital X�ray systems, this

condition is not met because of wide dynamic range. The

relationship between radiation dose required to detect an

element of area S = ∆x∆y and contrast K = aeff∆z in a

phantom of thickness Z is given by the following equation

[5]:

D = [Ψt(1 + δ)laeffZ]/[A∆x∆y(aeff∆z)2η] , (1)

where Ψt is threshold signal/noise ratio; δ is secondary�

to�primary radiation ratio in the detector input plane; A is

a coefficient proportional to the number of quanta per

background image area unit at given X�ray hardness; aeff is

effective linear extinction coefficient; η is detective quan�

tum efficiency.

It follows from Eq. (1) that under otherwise identical

shooting conditions (aeff = const) of the same phantom

(invariability of S, K, Z), the dose reduction to limiting

value is determined as:

B = (1 + δ)/η. (2)

In the case of an ideal apparatus (object scattering is

absent) δ = 0, η = 1, and B = 1. Therefore, Eq. (2) shows

the dose magnification in an actual apparatus relative to

the ideal apparatus. The dependence of В on δ at differ�

ent quantum efficiency η is shown in Fig. 2.

At limiting quantum efficiency (η = 1), radiation

dose is determined by scattered radiation:

B = 1 + δ. (3)

It follows from Fig. 2 that the reduction of limiting

quantum efficiency should be achieved. It follows from

Eq. (1) that X�ray hardness increase above values typical

of analog X�ray is a promising approach to reduction of

radiation load and scattered radiation.

It also follows from Eq. (1) that not only quantum

efficiency, but also X�ray hardness, element area, and its

contrast should be specified to provide correct compari�

son of working doses of X�ray apparatuses.

Mammography and CT can be used to illustrate this

rule. High radiation load is required to resolve elements

25�50�µm in size and elements with contrast sensitivity

<0.5%.

The X�ray apparatus should provide image quality as

high as required for diagnosis.

A water phantom and detail–contrast test is required

to provide experimental comparison between working

doses of X�ray apparatuses.

Nuclear Ass CD RAD is the most popular

detail–contrast test. This test object is an clear plastic

plate with holes 0.3�8 mm randomly distributed over 225

cells (2 holes per cell).

The similar test object TDK�1 is available from

Amico, Ltd. (Russia). The holes in the TDK�1 test object

are 0.5�8 mm with one hole at the center of the cell. The

two test objects allow the detail–contrast boundary to be

resolved. Different hole location implies different visual

discernibility: two holes per cell activate the so�called

crowding effect [4], whereas one hole per cell activates the

yes–no principle. Estimation unification is important.

4. Image Processing and Presentation

Multivariance of scialogical presentation of norm

and pathology and abruptness of their projection combi�

nation in roentgenograms prevent the solution of the

problem of automatic resolution of norm and pathology.

Even in the 1950s, automatic decision�making systems

have been applied to X�ray diagnosis [3]. None of meth�

ods tested was introduced into clinical practice. This

problem (revolution in radiation diagnosis) should be

solved in the XXI century.

Computer�assisted X�ray diagnosis (expert systems)

offers more promising results. Digital algorithms for

detection of pathological lesions are available from some

manufacturers. For example, a computer�assisted digital

mammograph for detecting malignant tumors is available

from General Electric. Similar equipment is available

from Meditsinskie Tekhnologii, Ltd. (Russia).

X�Ray images are presently displayed as shades of

gray, i.e., without capacity of color vision in information

B

Fig. 2. Dependence of В on δ at different quantum efficiency η.

218 Blinov and Mazurov

extraction. Color encoding of X�ray image and spectro�

zonal X�ray television is not used extensively, but they are

very promising. First, color encoding of X�ray image is

promising for 3�D imaging in CT. This direction is being

extensively developed. Numerous CT sections contain a

huge amount of information that is difficult to process.

Synthesis of volume 3�D image from sections and their

painting into pseudocolors provide a promising approach

to this problem.

However, many problems of 3�D color presentation

of internal organs remain to be solved.

Many attempts for color contrasting of X�ray images

failed in clinical practice [6]. Perhaps this is due to many

phenomena of color vision resulting in hyperdiagnosis

[4]. In our opinion, color presentation of X�ray images

should not be discarded completely. Digital engineering

provides a new approach to color presentation of X�ray

images, including the principle of color encoding.

Although spectrozonal (multizonal) X�ray appara�

tuses have been studied for more than 50 years, they are

still laboratory devices. Two�zonal osteodensitometry and

two�energy subtraction resulting in imaging of soft tissues

and bones are exceptions to this rule.

Exchange of radiological information will be possi�

ble in the near future. The problem of development of X�

ray television in Russia remains rather urgent. A federal

program is required to solve this problem.

Most roentgenologists and roentgenographers prefer

film X�ray technology. There is a psychological barrier in

practical roentgenologists to replace film X�ray technolo�

gy. Special training of roentgenologists and roentgenogra�

phers is required. In Russia, this problem is aggravated by

the economic status of roentgenologists and roentgeno�

graphers.

Digital X�ray technology has given rise to interven�

tion radiology. Unfortunately, no special devices for inter�

vention radiology are available from domestic manufactur�

ers except for low�power surgical devices (bellow 3.5 kW).

Continuous X�ray viewing mode of intervention

radiology is not compatible with the mobility of organs

and detector inertia. As a result, high radiation load and

dynamic unsharpness are observed. Continuous X�ray

viewing mode should be excluded in new models of appa�

ratuses for intervention radiology. The viewing mode

should be implemented using short pulses with repetition

frequency compatible with the mobility of organs. Pulses

used in roentgenoscopy should have sharp leading and

trailing edges. X�Ray tubes with grid control should be

used in spite of their high cost.

Only basic problems of digital roentgenology have

been discussed in this work. The immediate prospects for

development of radiodiagnostic equipment based on dig�

ital systems for medical image representation and pro�

cessing have been considered. This research will be con�

tinued to implement the advantages of digital X�ray tech�

nology more completely.

It should be noted in conclusion that digital tech�

nologies would allow roentgenology to occupy the leading

place in radiological diagnosis.

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