Method and apparatus for calibrating a biopsy attachment for ultrasonic imaging apparatus

A sector-scan ultrasonic imaging apparatus includes a biopsy attachment mounted on the housing of the imaging apparatus for positioning a biopsy needle relative to the ultrasonic scan head of the imaging apparatus. An image display device displays both an image of the region scanned by the scan head and a predetermined, superimposed electronic representation of the position of the biopsy needle-line relative to the probe scan head. The biopsy needle-line is calibrated with a scan head coordinate system which defines a sector sweep of the scan head by determining the coordinates of the needle-line in the scan head coordinate system independently of determining the particular spatial relationship of the needle-line in operative position relative to the scan head. A calibration member adapted to be mounted on the biopsy attachment includes at least two ultrasonic reflection regions which are scanned by the scan head during the calibration mode and displayed on an image display device. The display of these at least two reflection regions enables the needle-line coordinates to be determined using the predetermined geometric relationship of the calibration member with respect to the imaging apparatus housing. Alternatively, the calibration member can include a single ultrasonic reflection region, and an angular detector can be used to determine the angular orientation of the calibration member relative to the probe scan head, to enable the needle-line coordinates to be determined.

FIELD OF THE INVENTION 
The present invention relates to a method of and apparatus for calibrating 
a biopsy attachment for ultrasonic imaging apparatus. 
BACKGROUND OF THE INVENTION 
In general, ultra-sound imaging techniques use a pulse-echo method wherein 
short pulses of ultrasonic energy generated by a piezoelectric transducer 
are focused to a narrow beam and transmitted through a suitable conducting 
medium, usually water, into the body of a patient. A portion of the 
ultrasonic energy is reflected back toward the transducer at tissue 
interfaces between various different bodily structures due to mechanical 
impedance discontinuities at the interfaces. The transducer receives the 
reflected energy and converts it into electrical signals. The time of 
arrival of the returning reflected signals indicates the relative 
positions within the body of the interfaces. In other words, the timed 
spacing between the reflected signals or echoes is proportional to the 
physical spacing of the respective reflecting interfaces within the body; 
and the amplitude of the echo is a function of the characteristics of the 
structures forming the interface. 
The image-representing electrical signals corresponding to the 
characteristics of the reflected mechanical energy are then displayed, 
generally, on a "B-scan" display. Such a display is comparable to a 
conventional television display. In such a system, the reflected echo 
signals modulate the brightness of the display at each point scanned. 
Strongly reflecting internal structures, such as hardened artery walls, 
appear brighter on the display than weakly reflecting structures. This 
gray scale produces a useful diagnostic tool. 
A plurality of scan lines can be produced by scanning the ultrasonic beam 
produced by the transducer at a predetermined rate and in a predetermined 
direction across the surface of the patient. The plurality of scan lines 
so produced can be used to yield a sector-shaped display of a 
cross-sectional picture in the plane of the scan produced by the 
reflector-scanner, which scans mechanically over a desired angle. 
A typical sector scan probe is illustrated in U.S. Pat. No. 4,151,834, the 
disclosure of which is hereby incorporated by reference. This patent shows 
a housing containing a DC servomotor that drives a mechanism for 
oscillating a transducer crystal. The transducer is periodically pulsed 
with electrical signals causing an ultrasonic beam to be emitted 
periodically as the transducer oscillates between its angular limits. The 
rate at which the transducer is pulsed is many times greater than the rate 
of angular movement of the transducer; for this reason, the beam is said 
to scan a sector. 
Some medical procedures are facilitated when a biopsy needle is used in 
conjunction with the ultrasonic probe, and for this reason, spatial 
ultrasonic probes have been developed to achieve this purpose. U.S. Pat. 
No. 4,108,165 discloses an ultrasonic probe having an annular transducer 
periodically driven by an electronic circuit for producing ultrasonic 
beams which can be directed into the body of a patient under examination. 
In the device disclosed in this patent, no scanning of the beam is 
provided, and the transducer is mounted in a cylindrical housing having an 
axial bore concentric with the annular transducer. The biopsy needle is 
concentrically located within the probe to align the biopsy needle with a 
biopsy target in the body under examination. 
In general, high accuracy biopsy can be accomplished using a biopsy 
attachment mounted on a scanning ultrasound probe where the attachment is 
of the type which includes a needle guide for orienting the biopsy needle 
accurately toward a biopsy target according to the following procedure. 
First, the patient is ultrasonically scanned and the biopsy target is 
located on the display screen. The display also includes a predetermined, 
superimposed electronic representation of the position of the needle-line 
relative to the probe scan head, where the needle-line is defined as the 
line along which the biopsy needle would travel while being inserted 
through the needle-guide. To align the needle-line with the biopsy target, 
the ultrasound probe is moved relative to the body under examination until 
the displayed needle-line passes through the image of the biopsy target on 
the display screen. In order to determine the distance to the biopsy 
target, a movable cursor associated with the display device can be moved 
to the displayed biopsy target. By calibrating the position of the cursor, 
the distance to the target can be determined. 
The above-described technique is generally illustrated by U.S. Pat. No. 
4,346,717 which discloses an ultrasonic probe designed to facilitate the 
use of a biopsy needle. This system produces and electronically 
superimposes on a display screen image of the body under examination a 
guide image beam which corresponds to the orientation of a needle guide 
for a puncturing biopsy needle. The coordinates of the guide image beam on 
the display screen are calculated by using the value of the angle .theta. 
which defines the angular relationship between the needle guide and the 
ultrasonic probe. An angle detector is employed for precisely detecting 
the angle of the guide sleeve relative to the ultrasonic probe. If the 
guide sleeve is arranged at a fixed angle .theta., aiming of the 
puncturing needle relative to the target area is accomplished by spatially 
displacing the ultrasonic probe on the surface of the body, and adjusting 
the attitude of the probe, until the guide beam superimposed on the 
displayed image passes through the biopsy target area to be punctured. If 
the position of the guide sleeve is adjustable with respect to the probe, 
adjusting the guide sleeve causes the guide image beam to likewise be 
adjusted via positioning signals which are obtained as a function of an 
angle-adjusting element which functions to reposition the guide sleeve; 
thus, the guide sleeve is moved until the guide image beam passes through 
the biopsy target shown on the display screen. 
Both the above-described general ultrasound biopsy procedure as well as 
that disclosed in U.S. Pat. No. 4,346,717 require the generation of a 
guide image beam which electronically represents the biopsy needle-line on 
the display screen and which is superimposed on the displayed ultrasound 
image of the scanned body section which includes the biopsy target. In 
heretofore known systems, in order to show the needle-line on the display, 
the system must determine, for example, by direct measurement or precision 
manufacturing, the geometry of the needle guide, and hence that of the 
needle-line, in the scan head coordinate system which defines the sector 
sweep of the ultrasound scanning head associated with the ultrasound 
imaging apparatus; this coordinate system can conveniently be expressed in 
polar coordinates employing the scan angle and the range r. 
However, in most ultrasound probe systems having biopsy attachments, 
although the spatial relationship between the needle guide and the housing 
is known because the biopsy attachment is mounted on the probe housing, 
the spatial relationship between the scan head and the probe housing is 
generally not precisely defined because the imaging system does not 
require it. As a result, the geometry of the needle guide in the scan head 
coordinate system is also not precisely defined. The system disclosed in 
U.S. Pat. No. 4,346,717 solves this problem by providing a needle guide 
attachment which is, unlike most ultrasound probe systems, precisely 
disposed at a known angle .theta. with respect to the ultrasound scan 
head. Disadvantageously, this requires a high degree of manufacturing 
precision with respect to the tolerances between the biopsy attachment, 
the probe housing, and the scan head, resulting in increased costs. It 
also requires calibration at the factory. Alternatively, as noted above, 
the system disclosed in U.S. Pat. No. 4,346,717 employs an angle detector 
to determine this angle, also resulting in additional components and 
increased costs. 
It would be advantageous to eliminate the necessity of determining the 
particular spatial relationship between the scan head and the needle-line 
in order to calibrate the biopsy attachment with the scan head coodinate 
system so that the needle-line can be superimposed on the display screen. 
It is, therefore, an object of the present invention to provide an 
ultrasonic imaging apparatus biopsy attachment calibration method and 
apparatus which provides this capability and which overcomes the 
above-described deficiencies in the prior art. 
SUMMARY OF THE INVENTION 
The present invention is particularly suitable to what is termed 
multiprocessor based realtime ultrasonic sector scanners, hereinafter 
termed ultrasonic imaging apparatus of the type described. An example of 
such apparatus is the Dynex line of ultrasonic imaging apparatus currently 
being marketed by Elscint, Inc., 930 Commonwealth Avenue, Boston, MA 
02215. 
Apparatus of the type described comprises an ultrasonic probe having a 
housing into which a scan head is mounted for oscillatory motion to define 
a sector-shaped scanning region (typically from 30.degree. to 60.degree.), 
and electronic processing and display circuitry for realtime processing 
and display of the signals developed by the probe. Such circuitry 
comprises memory means for storing data representative of an image of the 
region scanned by the head, and an image display means responsive to the 
memory means for displaying a realtime image of the region scanned by the 
scan head. The display means of the apparatus includes a processor for 
creating a cursor in the displayed image which is manually positionable by 
an operator to various locations in the displayed image, and for computing 
the coordinates of the location of the cursor in the scan head coordinate 
system. 
The housing of the probe is provided with a biopsy attachment for 
positioning a biopsy needle so that its needle-line has a particular 
spatial relationship with the scan head when the needle is mounted in 
operative position on the housing. The present invention provides for an 
improved method for aligning the needle-line with a biopsy target by 
creating a computer generated pseudo needle-line which is superimposed on 
the realtime image contained in the memory means. Such method is based on 
a calibration procedure that does not require independent determination of 
the particular spatial relationship of the actual needle line of a biopsy 
needle when the latter is in its operative position. In other words, no 
knowledge is needed of the relationship between the angle of the biopsy 
needle and the centerline of the scan head, for example, and the position 
of the biopsy attachment on the housing relative to the scan head, etc., 
because of the calibration procedure of the present invention. Such 
procedure includes mounting a calibration member on the biopsy attachment, 
immersing the member in a suitable fluid, e.g., water, operating the 
imaging apparatus to scan the calibration member, and storing the data so 
obtained in the memory means. The calibration member may have two spaced 
sonic reflection regions, preferably in the form of substantially 
spherical reflection members such that a line connecting the two regions 
is congruent to the biopsy needle-line when the biopsy needle is in its 
operative position. 
The two reflection regions appear as visually distinguishable bright spots 
in the display generated during the calibration procedure; and an 
imaginary line passing through the two spots defines the biopsy needle 
line in the display. The coordinates of the line passing through the 
bright spots are computer generated by sequentially moving the cursor into 
overlying relationship with each of the bright spots to allow the computer 
to acquire the individual coordinates of the spots in the scan head 
coordinate system. From this information, the computer then generates and 
stores the coordinates of the line passing through the two bright spots. 
Alternatively, only one reflection member can be used instead of two; but 
in this case, the computer must be furnished with the coordinates of the 
single bright spot, obtained by manually positioning the cursor on the 
spot, and with the angular relationship of the biopsy needle-line with 
respect to the scan head. With these data, the coordinates of the pseudo 
needle-line can be computed and stored. 
By following the above described calibration procedure, the memory means 
will contain data which, when the contents of the memory means is 
displayed, will produce a reference line of predetermined, visually 
distinguishable, intensity representing the calibration member. When the 
apparatus is used in a clinical imaging situation, the reference line will 
appear in the display superimposed on the clinical image. The reference 
line coincides with the biopsy needle-line when the needle is mounted in 
operative position even though the needle itself will not be visible in 
such image. 
In operation in a clinical imaging situation, the medical technician would 
adjust the ultrasonic imaging apparatus (without the biopsy needle mounted 
in operative position) relative to the patient until the reference line in 
the image passes through the biopsy target region in the image. In this 
position of the apparatus, the technician is assured that insertion of a 
biopsy needle into the biopsy attachment on the housing of the apparatus 
will result in the penetration of the needle into the target region. 
The invention is also applicable to ultrasonic imaging apparatus of the 
type described wherein the probe is provided with a biopsy attachment that 
is adjustable to more than one position such that the angle made by the 
biopsy needle relative to the centerline of the probe head is selectively 
adjustable. The calibration procedure described above is carried out for 
each position of the biopsy attachment; and the computer stores the 
coordinates of the pseudo needle-lines such that they can be retrieved 
from memory in accordance with the particular adjustment of the the biopsy 
attachment in current use. The adjustment can be sensed by a transducer 
which will automatically select the appropriate coordinates to be used in 
a display; or, direct operator input can be used to specify the adjustment 
and effect selection of the appropriate set of coordinates.

DETAILED DESCRIPTION OF THE INVENTION 
Referring now to FIG. 1, reference numeral 10 designates a biopsy 
attachment according to the present invention attached to sector scan 
ultrasonic imaging apparatus 12. The details of imaging apparatus 12 are 
of no concern in the present application, and only transducer scan head 14 
is shown in detail. Transducer scan head 14 is mounted on bearing 16 
carried by a support 18 rigidly attached to imaging apparatus 12 adjacent 
open end 20 of housing 22 containing the imaging apparatus. Support 18 
carries a position sensor (not shown). By a suitable mechanism, such as a 
servo system (not shown), transducer scan head 14 is oscillated or scanned 
between two limits designated L1 and L2 in FIG. 1 which define a sector 
sweep. 
Open end 20 of housing 22 is closed by a plastic sheath 24, which is 
transparent to sonic radiation produced by transducer scan head 14 or 
reflected back to transducer 14 from an object producing an echo. Phantom 
line 26 defines the geometric center-line of the transducer; and the 
mechanism (not shown) housed within housing 22 causes the transducer to 
oscillate about bearing axis 26 producing a beam whose azimuth angle 
changes from the angular position shown byline L1 to the angular position 
shown by line L2. This movement occurs at around 30-70 scans per second, 
while the transducer is pulsed at a rate many times faster. As a result, 
many ultrasonic beams will be located within the sector sweep defined by 
the lines L1 and L2. 
When the scan head is commanded by the servo system to go to its zero 
position, the actual center line of the beam, as designated by broken line 
28, is displaced from the geometric zero position by the angle .alpha.. 
This angle is usually quite small and provides an error whose magnitude 
depends on the precision with which the electronics driving the transducer 
and the transducer mounting itself are fashioned. As discussed previously, 
a sector scan probe can have a DC motor which is servo-controlled and a 
support 18 to which is mounted a position sensor (not shown) which 
establishes the angle of the transducer and which feeds this information 
back to the motor for controlling its operation. By suitable calibration, 
the angle .alpha. can be made small. 
Biopsy attachment 10 includes tubular housing 30 formed of relatively thin 
plastic material dimensioned to closely fit around imaging apparatus 12, 
as shown in FIG. 1. The operational free end 32 of tubular housing 30 is 
open permitting plastic sheath 24 to project therethrough. The opposite 
axial end of housing 30 is also open and is threaded. Because 
sector-shaped imaging apparatus are generally tapered, as indicated in 
FIG. 1, tubular housing 30 is held in place with imaging apparatus 12 via 
screw cap 36, which is releasably connected to tubular housing 30 via 
screw threads 34 (shown in FIG. 5). Thus, tightening of cap 36 draws 
housing 30 into close engagement with imaging apparatus 12. Also, a groove 
(not shown) between probe end cap 36 and housing 30 includes a rubber ring 
seated over a thin protective drape, such that biopsy attachment 10 is 
held in place by tightening cap 36. This tightening encloses the rubber 
ring between biopsy attachment housing 30, cap 36 and the aforementioned 
groove and provides a very firm grip over imaging apparatus 12. 
In addition to tubular housing 30, biopsy attachment 10 includes needle 
guide means 40 mounted on tubular probe housing 30 via tubular housing 30, 
for orienting a biopsy needle toward a biopsy target. Needle guide means 
40 can be a bushing holder or lug, as illustrated in FIGS. 1 and 5, for 
receiving a bushing 87 of a calibration member 60 (FIG. 1) or a needle 
guide bushing 52 (FIG. 5) into which a biopsy needle 61 has been mounted, 
as disclosed in co-pending U.S. patent application Ser. No. 529,624, filed 
Sept. 6, 1983, the disclosure of which is hereby incorporated by 
reference. 
According to the present invention, calibration member 60 is mounted on 
biopsy attachment 10 by means of needle guide means 40 which, in the 
embodiment shown in FIG. 5, preferably includes a bushing holder or lug 40 
which includes spaced legs 42, 44, leading to recess 38. 
FIG. 2 illustrates calibration member 60 in an embodiment which includes a 
substantially straight rod 85 on which are mounted ultrasonic reflectors 
81, which are preferably substantially spherical balls, and a bushing 87 
preferably integral with or permanently affixed to one end of rod 85. 
Reflectors 81 can be integral with rod 85, or, alternatively, can be 
movably mounted thereon, e.g., they could be formed with a substantially 
central bore which frictionally engages rod 85. Rod 85 is preferably a 
small diameter rod or wire. Bushing 87 is adapted for mounting within 
needle guide means 40 of biopsy attachment 10. When calibration member 60 
is mounted within guide means 40, reflection members 81 are disposed such 
that they lie within the region of the sector sweep of scan head 14, and 
thus, will reflect a transmitted ultrasound beam back to transducer 14 
during a scanning operation. Accordingly, during a calibration scanning 
operation, the location of reflection members 81 will be displayed on 
image display means 90 associated with the ultrasonic imaging apparatus. 
Using this display, the coordinates of members 81 within a scan head 
coordinate system which is used to define a sector sweep of scan head 14 
can be determined and stored in memory unit 100. These stored coordinates 
are then used to calculate the coordinates of the biopsy needle-line in 
this same coordinate system. These biopsy needle-line coordinates are then 
stored in memory unit 100 where they can be used to provide a 
predetermined, superimposed electronic representation of the entire biopsy 
needle-line on image display means 90. 
One technique for determining the coordinates of reflection members 81 
includes, as shown in FIGS. 3, 4a and 4b, positioning a movable cursor 91, 
shown as a "cross", displayed on sector-shaped display screen 95 
associated with image display means 90 via cursor control means 93 which 
may be a joy stick or other positioning device. Cursor 91 is successively 
positioned at the displayed positions A and B of reflection members 81; 
these displayed positions are obtained after immersing calibration member 
60 including reflection members 81 in a fluid held by a small tank 130 
which may even be a styrofoam cup. The coordinates in the scan head 
coordinate system of cursor 91 at these points are then determined and 
stored in memory unit 100, for use in determining the coordinates of the 
biopsy needle-line. As before, the biopsy needle-line coordinates are 
stored, and subsequently used, as desired, to provide an electronic 
representation of the needle-line on the display device. Cursor control 
means 93 may be used to alter the position of cursor 91 by means of data 
signals provided by computer and memory unit 100 to image display means 90 
in any suitable manner known in the art. 
Adjustment means 110 shown in FIG. 1 provides for adjustment of the spatial 
relationship of needle guide means 40 relative to probe housing 22 and 
transducer scan head 14 such that the biopsy needle-line has a 
multiplicity of operative positions relative to scan head 14. At each 
setting of adjustment means 110, the biopsy needle-line has a particular 
spatial relationship in operative position relative to the scan head. For 
each such operative position, a separate calibration of the needle-line 
within the scan head coordinate system is necessary. Memory unit 100 is 
employed to store the biopsy needle-line coordinates for each operative 
position. The particular coordinates stored in memory unit 100 which are 
used to provide the superimposed needle-line display on image display 
means 90 will be determined by the setting of adjustment means 110. In 
FIG. 1, adjustment means 110 is shown in an embodiment which includes a 
plate 111 which is fixed to tubular housing 30 and onto which needle guide 
means 40 is movably mounted. 
FIG. 5 illustrates stop means 120 for stopping the insertion of a biopsy 
needle 61 in needle guide means 40 at a range corresponding to the 
position at which a biopsy target is located. Stop means 120 in one 
embodiment can be a sleeve 121 having an adjustable length. The sleeve 
length corresponding to the desired range for the specific needle length 
can be selected or cut, and mounted on the biopsy needle. Alternatively, a 
conventional needle stop could be employed, e.g., a stop comprising a ring 
having a central bore which can be adjustably secured on the biopsy needle 
via a side screw which frictionally contacts the needle. 
By the above method and apparatus, the coordinates of the biopsy 
needle-line in the scan head coordinate system are determined 
independently of determining the particular spatial relationship of the 
needle-line in a particular operative position relative to the scan head. 
Using the method and apparatus of the present invention, there is no need 
to determine the particular spatial relationship of the needle-line 
relative to the scan head when the needle is in operative position 
relative to the scan head. This provides a simpler, less expensive device 
than has been heretofore known, eliminating the need for providing high 
mechanical tolerances in manufacturing the ultrasonic probe housing, the 
transducer scan head and the biopsy attachment as a precondition to 
determining the needle-line coordinates in the scan head coordinate system 
for superimposing the needle-line on the probe display. 
It should be noted that calibration member 60 is not limited to the 
particular structure shown in FIG. 2, but that alternatively rod 85 can be 
provided with many different shapes. Also, rod 85, bushing 87, and 
reflection members 81 can be formed as a single integral unit or as an 
assembly. Alternatively, members 81 can be movably mounted on rod 85, 
e.g., as discussed above. Moreover, reflection members 81 can be spherical 
in shape, or can have other alternative shapes, with the sole requirement 
being that members 81 must reflect the transmitted ultrasonic beam back to 
transducer 14. Thus, it can be seen that, as an additional alternative, 
reflection members 81 can be formed as "holes" in an ultrasound 
transparent material. 
Preferably, when calibration member 60 is mounted in guide means 40, 
substantially straight calibration rod element 85 will be disposed along 
the line along which a biopsy needle would be disposed were the biopsy 
needle mounted on the biopsy attachment. This eliminates the need for 
additional computations which would otherwise be necessary, based on a 
known pre-determined geometrical relationship between the orientation of 
rod 85 and probe housing 22, to obtain the coordinates of the biopsy 
needle-line in the scan head coordinate system once calibration member 60 
has been scanned by the probe during the calibration mode. However, it 
should be noted that so long as the orientation of rod 85 bears a known 
geometrical relationship with respect to probe housing 22, and thus with 
respect to the biopsy needle-line, the desired coordinates of the 
needle-line in the scan head coordinate system can be obtained through 
easily derived mathematical methods. In other words, although calibration 
member 60 is preferably in the shape of a needle, i.e., small-diameter, 
substantially straight rod 85, member 60 need not be provided with this 
shape. Any calibration member which is affixed to probe housing 22 with a 
known, defined geometry and which has ultrasound reflection regions 
capable of reflecting a transmitted ultrasound beam back to the transducer 
and, as a result, capable of precisely geometrically defining the 
orientation of the biopsy needle guide hole, may be employed to provide a 
calibration member. Therefore, a "phantom" member 200 (FIG. 6) which has 
any desired arrangement of ultrasound reflection members, or regions 81, 
on which a geometrically defined structure will be placed or attached 
which enables the probe housing to be mounted or attached to "phantom" 
member 200 in a geometrically defined manner in order to provide a 
capability of determining the orientation of the needle-guide hole in the 
scan head coordinate system could be employed as a calibration member 
according to the present invention. 
FIG. 6 discloses an alternative embodiment of the present invention which 
includes a calibration member 200 which includes second housing 201 and 
mounting means 203 for mounting imaging apparatus 12 and biopsy attachment 
10 mounted thereon on second housing 201 in a predetermined geometrical 
relationship such that needle-line N of the biopsy needle is defined. At 
least one reflection region 81 is disposed in housing 201 on any 
convenient point on needle-line N, although a plurality of members or 
regions 81 could be employed if desired. Housing 201 can include a 
reservoir for holding fluid for use during calibration scanning by the 
scan head. Mounting means 203 can include means for mounting the imaging 
apparatus and the biopsy attachment mounted thereon in multiple discrete 
operative positions of the biopsy needle relative to the scan head mounted 
in the imaging apparatus housing. It should be noted that only one 
reflection region 81 is necessary to determine the needle-line coordinates 
in the scan head coordinate system where the angular orientation of 
needle-line N relative to the scan head of imaging apparatus 12 is known. 
This angular orientation can be determined via precisely manufacturing the 
various parts, or, alternatively, via angle measurement means which can be 
provided to measure this angular orientation. Thus, by determining the 
coordinates of a single reflection region 81, the coordinates of each 
other point along line N can also be determined from the predetermined 
angular orientation between needle-line N of calibration member 200, and 
the scan head. In other words, when the angular orientation of the 
needle-line N is determined, the set of possible orientations for 
needle-line N includes all parallel lines having this given angular 
orientation; from a mathematical perspective, it is clear that by locating 
one point along the actual line N, the coordinates of the entire line N 
can be determined. 
Referring again to FIG. 1, calibration member 60 need only include at least 
one reflection member or region 81 to reflect back the transmitted 
ultrasound beam to the transducer in the case where angle measurement 
means 181 is provided to measure the angular orientation of rod 85 
relative to probe housing 22, or alternatively, where this angular 
orientation is determined via other techniques, such as by precision 
manufacturing of biopsy attachment 10 mounted on probe housing 22, and 
calibration member 60 and the transducer scan head mounted in probe 
housing 22. As discussed above, one reflection member or region 81 in such 
case is sufficient because, by determining its coordinates, the 
coordinates of each other point along rod 85 are also known. Also as 
explained above, computer and memory means 100 is used to store data 
representing this measured or determined angular orientation and to 
calculate the coordinates of needle-line N for ultimate superimposed 
display on image display means 90. On the other hand, the needle-line 
coordinates can be determined totally independently of the predetermined 
geometric relationship between the needle-line and the scan head, (i.e., 
without determining the value of the angular orientation of the 
needle-line relative to the scan head and, further, without actually 
determining any other physical parameter relating to this geometric 
relationship, by using a calibration member which includes at least two 
reflection members or regions 81. In such case, during calibration 
scanning, the coordinates of at least two-positions on rod 85 must be 
determined in order to provide sufficient data for computer and memory 
means 100 to determine the orientation of the needle-line relative to the 
scan head coordinate system and to calculate the coordinates of the 
needle-line. 
According to the present invention, the above-described calibration can be 
performed either by the manufacturer at the factory or by the user. The 
needle-line coordinates can be, for example, fed into the ultrasonic 
imaging apparatus system computer non-volatile memory. The user need only 
check the probe needle-line calibration occasionally, and update the 
computer memory if necessary. 
From the foregoing description, one skilled in the art can easily ascertain 
the essential characteristics of the present invention and, without 
departing from the spirit and scope thereof, can make various changes and 
modifications of the invention to adapt it to various usages and 
conditions.