Note: Descriptions are shown in the official language in which they were submitted.
4 FIELD OF THE INVENTION
The field of art to which the invention pertains
6 includes apparatus and methods for arterial angiography in
7 which a single composite image is constructed from information
8 contained in multiple, serially obtained images.
lP BACKGROUND AND SUMMARY OF THE INVENTION
11 Arterial angiography as commonly practiced
12 involves an arterial injection of a contrast medium opaque
13 to X-rays and subsequent X-ray photography of the artery
14 section of interest distal to the injection. A single
picture or series of pictures of the artery section is taken
16 as the contrast medium flows therethrough. A large amount
17 of contrast medium is required in order to provide sufficient
1 contrast to highlight the artery edge profile in each
19 picture. Injection of this large amount of contrast medium
2 poses a significant risk of trauma or fatality. As an
21 example, coronary angiography has a fatality risk of the
2 order of 0.01 to 0.001. On the other hand, if the contrast
2 medium is injected in a vein, there is much lower risk of
2 adverse consequences of the order of 0.0001. However, the
2 resulting X-ray image has low contrast because of mixture,
2 thereby dilution, of the contrast medium with substantial
, . ,,, ~
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1 amounts of blood by the time it reaches the artery of
2 interest. This low contrast makes it difficult to precisely
3 define the artery edge, thereby making it difficult for a
skilled person to determine whether corrective therapy is
appropriate.
6 The present invention discloses a method and
7 apparatus which eliminates the above-described disadvantages
8 of current angiography, angiography being defined as any
9 method for visualizing a blood vessel, the edge or lumen
usually being of interest. Specifically, one aspect of the
11 invention utilizes venous injection of the contrast medium
12 while still providing an image which has a contrast equal to
13 or better than that of an image obtained after direct
14 arterial injection of the contrast medium. The method
according to the invention includes the steps of injecting a
16 contrast medium so that it will mix with blood to flow
17 through a vessel or artery section of interest, obtaining
18 multiple images of the vessel section as the blood/contrast
19 medium mixture flows therethrough, and synthesizing a single
composite image of the vessel section from information
21 contained in the multiple images. In specific embodiments
22 of the invention, a contrast medium opaque to X-rays is
23 utilized. The vessel is irradiated by an X-ray source, the
24 rays passing therethrough forming an image on an appropriately
positioned X-ray sensitive film/screen combination. The
26 synthesizing step includes registering the multiple im~ges
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1 from landmarks that are contained within the patient
2 and that have a relationship to the vessel of interest,
3 and identifying density indices of corresponding segments of
4 the registered images. A single image having corresponding
~ indices either averaged or cumulatively added is formed from
6 the identified density indices. In one embodiment, when the
7 vessel does not move, the synthesizing step can include
8 manually overlapping and registering transparent image
9 negatives so that one may look through the registered
negatives to observe the artery edge. This embodiment can
11 be utilized for only a limited number of negatives because
1 their cumulative opasueness will soon mask the detail
1 required for vessel resolution. In a preferred embodiment,
1 computer technology is utilized whereby each image segment
1 or element is assigned a digital representation according to
1 its average density, a synthesized image being formed by the
1 computer based upon the density information of each corres-
1 ponding image segment.
1 One may utilize an X-ray sensitive phosphor
2 in lieu of the X-ray sensitive film/screen combination, the
2 phosphor being electronically scanned and the resultant
2 signal being used to drive a video display tube or converted
2 to a digital format for computer storage and subsequent
2 processing.
2 If the vessel is moving during the time interval
2 ~uring which the images are obtained, a method of synthesizing
.~
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~ a co osite image includes the steps of defining anticipated
2 image profiles based upon average vessel edge profiles of
3 healthy vessels. The anticipated profile for the vessel at
4 rest, called a base profile, is defined. An anticipated
S profile for each of the subsequent images is then derived
6 with respect to the base profile. For example, an image
7 taken 1/6th of a second after the image corresponding to the
8 base profile would have a profile which represents the
anticipated position of the vessel edge 1/6th of a second
after that of the vessel edge corresponding to the base
~1 profile. Each image segment associated wi~h the second
~2 image is then corrected by an amount equal to the offset
13 between the base profile and the anticipated vessel edge
14 profile for that picture, the correction being made so as to
51 ascertain the position of the vessel edge at the time of the
16 base profile position. This process is repeated for each of
17 the subsequent images, thereby providing images in which all
18 of the vessel edges are corrected so that they correspond to
19 the time of the base profile. This offsetting can be most
efficiently accomplished by a computer. Once the corrected
21 images are developed, a synthesized image can be obtained
~2 as explained above.
23 Although in the preferred embodiment multiple
24 images are obtained using X-ray photography, other techniques
for obtaining vessel edge profiles could also be utilized.
26 According to another aspect of the invention, the images
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1 could be obtained by the use of ultrasonic diagnostic
2 instruments which are capable of distinguishing one type of
3 tissue characteristic from another, thereby eliminating any
4 need for injection of a contrast medium. When sound travels
through 60ft tissue it suffers attenuation which increases
6 with frequency. The greater the attenuation, the higher the
7 relative reduction in the high frequency components. Means
for developing a pictorial representation of the attenuation
9 and reduction in high frequency components are well known in
1 the art and can provide an alternative method of obtaining
1 multiple images of the vessel, the images obtained being
12 ¦ processed in the same manner as the X-ray images described
13 ¦ above.
14
15 l
16 ¦ BRIEF DESCRIPTION OF THE DRAWINGS
17 ¦ Fi~ure 1 is a perspective view showing the
1~ ¦ apparatus used in the present invention;
19 Figures 2A-2D are diagramatic representations
20 ¦ showing development of a composite angiogram from a series
21 ¦ of X-ray images;
22 l
23 ¦ Figure 3 is a diagramatic representation showing
24 ~ an embodiment utilizing a digital system to synthesize a
25 ~ composite image;
1 6-
Figure 4 illustrates a second embodiment of the
invention in which images are formed on an X-ray responsive
phosphor, the pattern of each phosphor image being electron-
ically recorded, processed and displayed;
Figures 5A and 5B are diagramatic representations
showing a method of synthesizing a composite image of a
vessel whose profile is changing as multiple X-ray images
are being obtained; and
Figure 6 illustrates a third embodiment of the
invention in which images are formed from reflected ultrasonic
waves.
DETAILED DESCRIPTION
The invention provides an apparatus for and a
method of arterial angiography in which a contrast medium is
injected at a point distant from an artery or vessel of
interest, the medium being mixed with blood prior to flowing
through the vessel of interest. Multiple images are obtained
of the vessel as the mixture of medium and blood flows
therethrough. The multiple images are registered so that
density image information from each can be combined into a
single composite image having a vessel edge much more
clearly defined than that of any of the multiple images.
This more clearly defined vessel edge allows a skilled
person to more accurately decide as to the advisability of
corrective therapy.
7.
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`I
1¦ Referring to Figure 1, the basic apparatus
21 necessary to practice the teachings of the invention are
31 shown. An X-ray source 10 is directed at a patient 12
~¦ resting on a table 14. Located directly beneath the patient
5 ¦ is a medium sensitive to X-ray irradiation which in this
6 ¦ first embodiment is an X-ray sensitive film/screen combin-
7 ¦ ation appropriately positioned within a camera 16. The
8 ¦ camera 16 is adapted to take multiple images at a rate of
9 ¦ approximately 6 frames per second although higher or lower
lO ¦ rates can be utilized. Images obtained from the camera 16
11 ¦ are processed in a manner to be explained belcw by a processing
12 ¦ means 18, the output of which is a single synthesized
13 ¦ composite image 20 derived from all of the images obtained
14 ¦ by the camera 16. Again it is emphasized that since the
15 ¦ contrast medium has been injectea at a point distant from to
16 ¦ the vessel of interest, for reasons as explained above, any
1~ ¦ single image of the vessel having the contrast medium
18 passing therethrough would have insufficient resolution to
19 accurately determine location of a vessel edge. However,
2Q multiple images of the vessel obtained while it contains a
21 diluted contrast medium, and thus a contrast medium concen-
22 tration less likely to cause harm to the patient, can be
23, combined to provide a composite image which will have the
24 same or superior resolution with respect to images obtained
from a more concentrated mixture of blood and contrast
26 medium.
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1 In one embodiment of the invention, image regis-
2 tration is effected by physically aligning each image
3 according to a landmark or landmarks within the patient such
4 as a bone, catheter, or any other item somewhat opaque to
X-rays. The thus registered images will constitute a
~ composite image having a resolution greater than that of any
7 single image. This embodiment is limited to only a few
images because the cumulative opaqueness of a large number
9 of images will mask the detail necessary for proper vessel
10 resolution .
11¦ Referring to Figures 2A-2D, a series of X-ray
12¦ images Il, I2 ... In is obtained by the camera 16, the
13¦ letter n representing the total number of images. It is
14¦ important that each X-ray image have at least one registration
15¦ landmark as above explained, the landmark having a predeter-
16¦ mined relationship to the vessel section of interest so that
17 slight movements by the patient and vessel which result in
18 misregistration of the various images with respect to the
19 vessel can be corrected. Referring to the first image Il,
two such means are shown, the first being a catheter 30
21 located within the patient's body and the second being a
22 bone segment 32. Also shown is a somewhat indistinct vessel
23 section 34, the edges of which are to be defined. Upon
24 registration of the images Il through In~ a co~posite
2~ image is derived as shown at Ic.
26 ___
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1 The composite image Ic can be synthesized by
2 many methods, all of which are diagramatically represented
3 as the processing means 18 shown in Figure 1. One method
4 which can be used when the vessel is immoble is to manually
overlap and register the transparent images Il through
6 In as previously described then view the composite image
7 Ic formed ~y the thus registered individual images. The
8 viewing can be accomplished by back lighting the image
9 array. To understand this method, and subsequent methods to
be explained below, assume that each image Il through In
11 consists of a series of image segments or elements, one
12 segment of which would be Sl in image Il, S2 in image
13 ¦ I2 and Sn in image In. Each segment Sl through SN
14 ¦ has a predetermined relationship to the landmarks, i.e. to
15 ¦ the catheter 30 or the bone segment 32. The segment Sc
16 ¦ for the composite image Ic has a density egual to the
17 ¦ combined densities of its corresponding segments S
18 ¦ through SN of the series of images Il through In.
19 ¦ Another processing means 18 which can be employed
20 ¦ is shown diagrammatically in Figure 3 and consists of
2i ¦ digitizing a density index associated with each image
22 ¦ segment, and then combining the density indices of each
23 corresponding image segment of each of the images Il
24 through In to develop a composite image Ic. Equipment
to accomplish the above is well known in the digital processing
26 art. Briefly, the system consists of a light source 36, the
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l output of which is projected through one of the X-ray images
2 Il through In~ indicated at 37. A film digitizer 38, an
~ example of which is a D57 digitizer made by Dicomed Corporation,
4 converts the image into a series of digital words, each word
corresponding to the density index of an image segment. The
6 digitizer 38 consists of an electronic image disector camera
7 40, deflection and control circuits 42 and an analog to
8 digital converter 44. The deflection and control circuits
9 42 control operation of both the image disector camera 40
and the analog to digital converter 44. The digital output
ll of the film digitizer 38 is provided to a digital computer
~2 46 and stored for subsequent processing. A computer which
13 could be used for this purpose is the Digital E~uipment
14 Corporation PDP ll-45 although many other commercially
l~ available computers could also be utilized. After subsequent
16 images I2 through In are digitized and stored in the
17 computer 46, the computer can combine the corresponding
18 image segment density information in any desired way, such
19 as by addition or averaging, to derive a new density index
for each picture segment. The output of the computer 46,
21 which consists of these derived density indicies, is provided
22 to a picture recorder 48 which in turn outputs a composite
23 image Ic based on the derived density indices. As one can
24 appreciate, the system above describd can provide a composite
image Ic having each image segment corresponding to the
average density of that segment in the preceding images I
,. 11.
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1 ~ thr ugh In~ ~>r a composite image having each image segment
2 ¦ corresponding to a summation of the density information of
31 that segment in the preceding image Il through In. All
41 of the above described individual image processing method
5 1 steps and apparatus components are well known in the
6 ¦ digital processing art for other and diverse purposes.
7 ¦ A further embodiment of the invention, shown in
8 ¦ Figure 4, utilizes the same X-ray source lO of the first
9 ¦ embodiment to irradiate a patient 12 laying on a table 14.
lO ¦ However instead of the camera 16, the X-rays, after having
ll ¦ passed through the patient 12, irradiate an X-ray sensitive
12 ¦ phosphor contained within an image intensifier tube/scanner
13 ¦ combination 58. If the vessel being X-rayed is relatively
14 ¦ motionless, the output of the image intensifier tube~scanner
15 ¦ combination 58 can be displayed by a video display unit 60
16 ¦ of the type that holds successive scans up to at least 30,
17 ¦ thereby allowing a composite image Ic to be developed as
l~ ¦ each subsequent image I2 through In is provided to the
~9 1 display unit 60. One example of such a video display unit
i5 a ~lodel 639 Scan Converter manufactured by Hughes Aircraft
21 ¦ Company. Alternatively, the output of the image intensifier
22 ¦ tube/scanner 58 can be provided to an analog to digital
23 converter 61, the output of which is provided to a digital
24 ¦ computer 62 which can process information from the various
2~ ¦ images Il through In as previously described to form a
26 ¦ composite image Ic. The composite image can be displayed
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1 in many ways, one example of which would be by a standard
2 television monitor 64.
3 Movement of the blood vessel during the image
4 taking interval makes registration more difficult. One
method of effecting registration, diagramatically illustrated
6 in Figure 5, comprises establishing a base line position for
7 the vessel edge, the base line Bl corresponding to an
8 anticipated vessel edge profile in the first image Il.
9 The base line Bl can be manually defined by a skilled
person. From this base line position Bl, an anticipated
vessel edge position B2 through Bn for each of the
12 subsequent images I2 through In is defined based upon
13 knowledge as to the movement of an averase vessel during the
14 time interval between each image. Having established the
anticipated profiles Bl through Bn~ one can derive an
16 anticipated offset for the vessel edge of each image I2
17 through In with respect to the base profile Bl. Vessel
18 edge profiles Bl through Bn wh,ch correspond to images
19 Il through In are shown in a vessel edge correction
chart 65. Using the second image I2 as an example, each
21 segment of the image I2 is offset by an amount equal to
223 the anticipated offset B2_gl Of its vessel edge with
respect to the base line profile Bl Thus a first image
24 segment 68 of the second image I2 located along the
abscissa at xl, would be offset towards the base line B
26 by a first ~ffset distance 70 equal ~o the value of B2-B
i 113~3575
1 ¦ at Xl. Similarly, a second image segment 72 located along
2 ¦ the abscissa at X2 would be offset towards the base line
31 Bl by a second offset distance 74 equal to the value of
41 B2-Bl at x2. After each of the images I2 through
5 ¦ In are corrected in accordance with the above, a composite
image Ic shown at 76 and a composite vessel edge 77 are
7 ¦ synthesized as previously explained. However, by using
8 ¦ high-speed X-ray camera eauipment currently available,
9 ¦ movement of the vessel during the time interval over which
lO ¦ the images are obtained will be small with respect to the
11 ¦ allowable uncertainty in vessel edge location, thereby
12 ¦ making the somewhat elaborate method described above
13 ¦ unnecessary.
14 ¦ Utilizing the present invention, the estimated
1~ ¦ vessel edge finding error is q~ite low. This can be
16 ¦ illustrated by an example in which 100 cc of Hypaque 75
17 ¦ Mr(385 mg iodine/ml) is venously injected in the arm
18 ¦ whereas the X-ray site is in the femoral artery. The
19 estimated blood volume between the injection sight and the
20 ¦ X-ray site is 1500 ml. For an injection duration of 4
21 ¦ seconds and an injection rate of 25 ml per second, it is
22 ¦ estimated that peak concentration in the femoral artery to
23 ¦ be X-rayed is 23.1 mg of iodine per ml of fluid present in
24 I the vessel. A concentration greater than 80% of the peak
2~ ¦ concentration, or 18.5 milligrams of iodine, will be present
26 ¦ in the artery for five seconds. Thus 30 images of the
Il ~13~575 ~
I
1 ¦ artery can be taken utilizing a frame rate of 6 frames/second.
2 ¦ The standard deviation of a vessel edge in a low-contrast
3 ¦ image from which a skilled person can locate the artery
41 edge is estimated to be 400 microns, whereas the standard
~¦ deviation for 30 images combined as above-described is
~¦ estimated to be 73 microns (400 divided by the square root
7 ¦ of thirty). Thus one can appreciate that the invention
8 ¦ teaches a method for obtaining a more precise definition of
9 ¦ the artery edge without the high concentration contrast
10 ¦ medium which would be required if the medium were injected
11 ¦ directly into the artery of interest.
12 ¦ A second example utilizes a coronary artery as
13 ¦ the X-ray site and as an injection site a distant pulmonary
14 ¦ artery selected so that approximately 500 ml blood is
15 ¦ contained between the injection site and the X-ray site.
16 ¦ An injection of 100 cc's of Hypague 75 Mr during a 4
17 ¦ second interval results in a peak concentration in the
18 ¦ coronary artery of 56.4 mg of iodine per ml of fluid.
19 Concentrations exceeding 80 percent of this peak concentration
20 ¦ will occur for 2.5 seconds, thereby allowing at a rate of
21 6 images per second 15 i~ages to be obtained. The standard
~2 deviation of a single image in this instance would be 170
23 microns and the standard deviation of the 15 images when
24 combined according to the principles of the invention
~5 will be 43.9 microns.
26 ___
1~385'7S
., ~
1 ¦ A third embodiment of the invention utili7es
2 ¦ ultrasonic imaging as a non-invasive alternative to the
3 injection of a con.rast medium into a patient, although a
4 contrast medium could be utilized in conjunction with
ultrasonic imaging. It is theorized that this method is
~ most useful when the artery sec~ion of interest is within a
7 few centimeters of the skin and is not obscured by bone or
8 gaseous-containing structures. The carotid artery meets the
9 above requirements and is medically significant because of
the frequent build-up of atherosclerotic plaque. Instrument-
11 ation currently available is capable of producing an image
12 ¦ of calcified plaGue having a resolution of approximately 1 mm.
13 ¦ Referring to Figure 6, a patient 90 is shown
14 ¦ on a supporting table 92. An ultrasonic wave transmitter
15 ¦ and receiver 94 is positioned so that radiating ultrasonic
1~ ¦ waves 96 will intersect an artery section of interest 98.
17 ¦ The ultrasonic transmitter is chosen to radiate in the
1~ ¦ frequency range between 1 MHz and 10 MHz, although both
19 ¦ higher and lower frequencies could also be utilized consistent
2~ ¦ with patient safety. The ultrasonic waves 100 reflected
21 ¦ from the artery section of interest 98 are converted to an
22 ¦ image by an the ultrasonic transmitter and receiver 94, many
23 ¦ types of which are commercially available. Multiple images
24 ¦ of the artery section are obtained and processed by a
25 ¦ processing means 104 as previously described, the output
26 being a composite image 106. A bone 108 or catheter 110 can
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1 be used for registration of the multiple images. Alternatively,
2 a separate ultrasonic receiver 112 could be positioned below
3 the patient 90 for conversion of the waves 114 passing
4 through the patient 90 to an image to be supplied to the
sl processing means 104.
