European Journal of Radiology. 13 ( 199 1) 50-54 50
0
EURRAD
1991 Elsevier
Science Publishers
B.V. 0720-048X/91/$03.50
00177
Peripheral DSA with automated stepping U. Fink ‘, S.H. Heywang ‘, T. Hilbertz 2, K. Fischer2, ‘Radiological Department,
University of Munich, Klinikum GroJhadern,
(Received
13 August 1990; accepted
Key words: Angiography,
E. Jenner2 and W. Buchsteiner2
Miinchen, and 2Siemens
after revision 29 January
DSA; Angiography,
comparative
Co., Erlangen,
F.R. G.
1991)
study
Abstract Peripheral digital angiography can be applied with automated stepping and in digital subtracted technique to evaluate the complete lower extremities angiographically with one single injection of contrast medium. Altogether 25 DSA-examinations were compared with nonsubtracted technique. By DSA-technique additional series could be reduced to only those, where significantly different flow in both extremities necessitated different timing as known from conventional angiography. DSA-technique with automated stepping may in the future totally replace conventional angiography of the peripheral arteries.
Introduction Peripheral angiography remains the first choice among examination methods prior to a possible interventional radiological or vascular surgical procedure. It is possible to accurately assess most vascular changes in the lower extremities. Conventional angiography with stepping has largely been replaced by digital subtraction angiography (DSA), recently, also with automated stepping [ 11. The aim of this study was to examine the possibilities to obtain complete digital subtraction angiographies with stepping and to evaluate whether further improvement of the diagnosis can be achieved by this. Material and Method A Multiskop C-arch unit with universal collimator, a 40 cm image intensifier and a Polytron 1000 VR with an image matrix of 1024 x 1024 pixels were used. The C-arch system in combination with a high-performance microprocessor system enabled fast and vibrationless unit movements.
Priv. Doz. Dr. Ulrich Fink, Radiology Department, Klinikum Groghadern, Marchioninistr. 15, D-8000 Miinchen 70, F.R.G.
Since the transparency of the object changes considerably in an examination with stepping, special control of the exposure parameters was required. These were recalculated for each position during stepping in order to keep the exposure constant and the tube voltage at an optimum value for iodine contrast (64 kV). The starting point was the transparency in the pelvic region during fluoroscopy. The density value was reduced at each step; a ‘typical’ patient being used as basis. Two images per second and maximum duration of 40 s were selected for peripheral angiography with stepping mode. Overtable position of the image intensifier proved to be optimal. Nevertheless, the legs of very adipose patients needed to be elevated in order to obtain the smallest possible magnification and thus the largest possible image section. To avoid motion artifacts, the patient’s feet were immobilized in an internal rotation position. In addition, a plastic bag filled with 4-5 liter ultrasound gel and 50 ml of 60% contrast medium was placed between the legs to balance the lower density between them. In each stepping position, the required universal collimator settings were made in a preparatory phase and stored automatically. As a rule, 4-5 steps were necessary per examination. After obtaining the collima-
Fig. I. Digital angiography (a-c) and DSA (d-f) with stepping in a patient with a femoral-popliteal bypass on the right side and several severe stenoses in the left femoral artery. Better imaging of stenoses and lower leg arteries with the subtraction technique.
52
tor settings in the last stepping position, the C-arch was moved back to starting position. The images were displayed unsubtracted. After the vessels had been sufficiently contrasted, stepping was triggered. To enable subtraction, a separate mask without contrast medium was exposed in the acquisition phase before contrast medium injection. A positioning accuracy of the unit movements of 0.1 mm was obtained. To obtain images without edges, it was necessary to have absolute coincidence of the universal collimator settings between pre- and postcontrast exposures. To achieve the required accuracy of 0.3 mm, the lamellae of the universal collimator must have a positioning accuracy of 0.07 mm. To produce the subtraction, the optimum filled image of the first position was selected in unsubtracted display and subsequently switched to subtracted display with an arbitrary mask image. The subtraction images produced could be further optimized, e.g., by windowing, filtration and pixel shift. Pixel shift was particularly important, since about 50 seconds passed between acquisition of the mask and acquisition of the contrast image and patient movements therefore occurred frequently.
Digital peripheral angiography with stepping was performed in a total of 25 patients with grade II to IV arterial occlusions. Twelve patients had bilateral occlusions of the iliac or femoral artery, while unilateral occlusion of the iliac or femoral artery was present in six. Seven patients had severe peripheral stenoses. 60-80 ml of a non-ionic contrast medium (300 mg iodine/ml) were injected per series with a flow rate of 8-10 ml/s. Results The angiographies were independently assessed by two experienced radiologists. All series were diagnostic down into the distal lower leg region in the case of digital, unsubtracted angiography in 15 and in 18 examinations at DSA. No additional series were necessary in these cases (Fig. 1). With both techniques, the images were diagnostic only down to both knees in 6 examinations and additional series had to be obtained for the lower leg region. Because of timing problems with unilateral occlusions, unsubtracted angiography was diagnostic only on one side in 4 cases and a total of 6 additional series had to
Fig. 2. Digital angiography (a) and digital subtraction angiography (b) in a patient with complete occlusion of the right iliac artery and clearly different flows. In the region of the knee and lower leg arteries subtraction technique was superior to non-subtracted technique because of disturbing bone shadows in the unsubtracted technique.
53 TABLE 2
TABLE 1 Digital angiography
versus DSA with automated
Digital angiography
stepping
versus DSA _____~
n (%I
Additional
DA DSA
15 (60) 18 (72)
-
down
DA DSA
6 (24) 6 (24)
6x1 6x1
Entire series diagnostic
DA DSA
4 (16)
3 x l/l x 3 1x1
Entire series diagnostic Series diagnostic to both knees
1 (4)
series
be obtained. On the other hand, this was necessary only in 1 case with DSA (Table 1). In the direct comparison between digital, unsubtracted angiography and DSA, there was an identical display in the pelvic region in 21 cases, in the thigh region in 19 cases, in the knee region in 17 cases as well as in the lower leg region in 11 cases. In one half of the patients DSA in the lower leg region was superior to digital, unsubtracted angiography (Fig. 2) mainly attributed to disturbing bone shadows with the unsubtracted technique (Table 2). In a total of 4 examinations, DSA was inferior to digital angiography due to patient movements primarily in the knee and lower leg region making exact subtraction impossible (Fig. 3). In the 3 cases, in which additional series were necessary with the subtraction technique, the patients had
Fig. 3. DSA (a) inferior to unsubtracted
Pelvis Thigh Knee Lower leg
DA > DSA
DA = DSA
-
21 (84”“) 19 (76”“) 17 (684,) 11 (44”“)
1 (4%) 2 (8%) 2 (8%)
exclusively unilateral different flows.
vascular
occlusions
DA < DSA 4 (16%) 5 (20%) 6 (24%) 12 (48%)
with clearly
Discussion With peripheral arterial DSA it is possible to achieve a reduction in the quantity of contrast medium required as well as better display of the lower leg arteries compared to the intravenous technique [2]. However, the disadvantage of this method is the need for injecting contrast medium several times. A further improvement in image quality can be achieved by using a high-resolution 1024 x 1024 image matrix [3,4]. With the unit described, it has been possible to perform complete digital angiography with automated stepping and thus a single administration of contrast medium in the digital, unsubtracted technique. However, additional series are often required in addition to the stepping series in the region of the knee joint and lower leg, especially if only one side can be adequately
angiography (b) in the region of the knee because of rotation movements mask and contrast images.
of the patient between the
54
displayed because of different flow on each side [ 51. DSA has been reported as the optimum examination technique, especially in the lower leg region [6]. Use was therefore made of experimental software to test the possibilities of the DSA with automated stepping. For good subtraction results in an examination with stepping and DSA, the individual components of an x-ray unit must fulfill certain requirements with regard to the reproducibility of the unit movements and collimator positioning, and the constancy of exposure between mask and contrast images. A positioning accuracy of the unit movements of 0.1 mm related to the patient plane is possible with the described system. DSA with automated stepping was possible in all cases examined. Additional series were necessary only because of rotation movements in the region of the knee (n = 4) or with unilateral vascular occlusions due to different flow on each side (n = 3). An essential prerequisite for the success is optimum timing of mask and contrast images. Furthermore, patient movements during the examination time must be prevented by optimum positioning. Conclusion: Peripheral DSA with automated stepping is an optimum substitute for conventional angio-
graphy with stepping. The number of additional series necessary in addition to the stepping series can be reduced to a minimum. It is possible to reduce both the necessary amount of contrast medium and time.
References Fink U, Heywang SH, Mayr B, Berger H. Subtracted versus nonsubtracted digital imaging in peripheral angiography. Eur J Radio1 1989; 9: 236-240. Triller J, Jegge P, Fritschy P, Fuchs WA. Peripheral venous and peripheral arterial digital subtraction angiography in occlusive diseases of the lower extremity. Digit Bilddiagn 1987; 7: 5-14. Hinz A, Langer M, Zwicker C. Arterielle digitale Subtraktionsangiographie der unteren Extremitlt mit hochaufliisender 1024er Bildmatrix. Rontgen Bl 1989; 42: 257-261. Fink U, Berger H, Mayr B, Hahn D, Ktiffer G. Comparison of digital angiography with DSA of peripheral arteries with 1024 x 1024 matrix. Radiology 1988; 169 (Suppl): 317. Fink U, Heywang SH, Berger H, Jenner E, Fischer K. First clinical results with digital peripheral angiography and stepping. Electromedica 1990; 58: 2-7. Neufang KFR, Gross-Fengels W, Beyer D. Bedeutung der Untersuchungstechnik und Bildnachverarbeitung fur die Qualittit der DSA der unteren Extremitat. Digitale Radiographie, Referate und Vortrlge, Schnetztor-Verlag, Konstanz, 1986, S. 221-229.
0
EURRAD
1991 Elsevier
Science Publishers
B.V. 0720-048X/91/$03.50
00177
Peripheral DSA with automated stepping U. Fink ‘, S.H. Heywang ‘, T. Hilbertz 2, K. Fischer2, ‘Radiological Department,
University of Munich, Klinikum GroJhadern,
(Received
13 August 1990; accepted
Key words: Angiography,
E. Jenner2 and W. Buchsteiner2
Miinchen, and 2Siemens
after revision 29 January
DSA; Angiography,
comparative
Co., Erlangen,
F.R. G.
1991)
study
Abstract Peripheral digital angiography can be applied with automated stepping and in digital subtracted technique to evaluate the complete lower extremities angiographically with one single injection of contrast medium. Altogether 25 DSA-examinations were compared with nonsubtracted technique. By DSA-technique additional series could be reduced to only those, where significantly different flow in both extremities necessitated different timing as known from conventional angiography. DSA-technique with automated stepping may in the future totally replace conventional angiography of the peripheral arteries.
Introduction Peripheral angiography remains the first choice among examination methods prior to a possible interventional radiological or vascular surgical procedure. It is possible to accurately assess most vascular changes in the lower extremities. Conventional angiography with stepping has largely been replaced by digital subtraction angiography (DSA), recently, also with automated stepping [ 11. The aim of this study was to examine the possibilities to obtain complete digital subtraction angiographies with stepping and to evaluate whether further improvement of the diagnosis can be achieved by this. Material and Method A Multiskop C-arch unit with universal collimator, a 40 cm image intensifier and a Polytron 1000 VR with an image matrix of 1024 x 1024 pixels were used. The C-arch system in combination with a high-performance microprocessor system enabled fast and vibrationless unit movements.
Priv. Doz. Dr. Ulrich Fink, Radiology Department, Klinikum Groghadern, Marchioninistr. 15, D-8000 Miinchen 70, F.R.G.
Since the transparency of the object changes considerably in an examination with stepping, special control of the exposure parameters was required. These were recalculated for each position during stepping in order to keep the exposure constant and the tube voltage at an optimum value for iodine contrast (64 kV). The starting point was the transparency in the pelvic region during fluoroscopy. The density value was reduced at each step; a ‘typical’ patient being used as basis. Two images per second and maximum duration of 40 s were selected for peripheral angiography with stepping mode. Overtable position of the image intensifier proved to be optimal. Nevertheless, the legs of very adipose patients needed to be elevated in order to obtain the smallest possible magnification and thus the largest possible image section. To avoid motion artifacts, the patient’s feet were immobilized in an internal rotation position. In addition, a plastic bag filled with 4-5 liter ultrasound gel and 50 ml of 60% contrast medium was placed between the legs to balance the lower density between them. In each stepping position, the required universal collimator settings were made in a preparatory phase and stored automatically. As a rule, 4-5 steps were necessary per examination. After obtaining the collima-
Fig. I. Digital angiography (a-c) and DSA (d-f) with stepping in a patient with a femoral-popliteal bypass on the right side and several severe stenoses in the left femoral artery. Better imaging of stenoses and lower leg arteries with the subtraction technique.
52
tor settings in the last stepping position, the C-arch was moved back to starting position. The images were displayed unsubtracted. After the vessels had been sufficiently contrasted, stepping was triggered. To enable subtraction, a separate mask without contrast medium was exposed in the acquisition phase before contrast medium injection. A positioning accuracy of the unit movements of 0.1 mm was obtained. To obtain images without edges, it was necessary to have absolute coincidence of the universal collimator settings between pre- and postcontrast exposures. To achieve the required accuracy of 0.3 mm, the lamellae of the universal collimator must have a positioning accuracy of 0.07 mm. To produce the subtraction, the optimum filled image of the first position was selected in unsubtracted display and subsequently switched to subtracted display with an arbitrary mask image. The subtraction images produced could be further optimized, e.g., by windowing, filtration and pixel shift. Pixel shift was particularly important, since about 50 seconds passed between acquisition of the mask and acquisition of the contrast image and patient movements therefore occurred frequently.
Digital peripheral angiography with stepping was performed in a total of 25 patients with grade II to IV arterial occlusions. Twelve patients had bilateral occlusions of the iliac or femoral artery, while unilateral occlusion of the iliac or femoral artery was present in six. Seven patients had severe peripheral stenoses. 60-80 ml of a non-ionic contrast medium (300 mg iodine/ml) were injected per series with a flow rate of 8-10 ml/s. Results The angiographies were independently assessed by two experienced radiologists. All series were diagnostic down into the distal lower leg region in the case of digital, unsubtracted angiography in 15 and in 18 examinations at DSA. No additional series were necessary in these cases (Fig. 1). With both techniques, the images were diagnostic only down to both knees in 6 examinations and additional series had to be obtained for the lower leg region. Because of timing problems with unilateral occlusions, unsubtracted angiography was diagnostic only on one side in 4 cases and a total of 6 additional series had to
Fig. 2. Digital angiography (a) and digital subtraction angiography (b) in a patient with complete occlusion of the right iliac artery and clearly different flows. In the region of the knee and lower leg arteries subtraction technique was superior to non-subtracted technique because of disturbing bone shadows in the unsubtracted technique.
53 TABLE 2
TABLE 1 Digital angiography
versus DSA with automated
Digital angiography
stepping
versus DSA _____~
n (%I
Additional
DA DSA
15 (60) 18 (72)
-
down
DA DSA
6 (24) 6 (24)
6x1 6x1
Entire series diagnostic
DA DSA
4 (16)
3 x l/l x 3 1x1
Entire series diagnostic Series diagnostic to both knees
1 (4)
series
be obtained. On the other hand, this was necessary only in 1 case with DSA (Table 1). In the direct comparison between digital, unsubtracted angiography and DSA, there was an identical display in the pelvic region in 21 cases, in the thigh region in 19 cases, in the knee region in 17 cases as well as in the lower leg region in 11 cases. In one half of the patients DSA in the lower leg region was superior to digital, unsubtracted angiography (Fig. 2) mainly attributed to disturbing bone shadows with the unsubtracted technique (Table 2). In a total of 4 examinations, DSA was inferior to digital angiography due to patient movements primarily in the knee and lower leg region making exact subtraction impossible (Fig. 3). In the 3 cases, in which additional series were necessary with the subtraction technique, the patients had
Fig. 3. DSA (a) inferior to unsubtracted
Pelvis Thigh Knee Lower leg
DA > DSA
DA = DSA
-
21 (84”“) 19 (76”“) 17 (684,) 11 (44”“)
1 (4%) 2 (8%) 2 (8%)
exclusively unilateral different flows.
vascular
occlusions
DA < DSA 4 (16%) 5 (20%) 6 (24%) 12 (48%)
with clearly
Discussion With peripheral arterial DSA it is possible to achieve a reduction in the quantity of contrast medium required as well as better display of the lower leg arteries compared to the intravenous technique [2]. However, the disadvantage of this method is the need for injecting contrast medium several times. A further improvement in image quality can be achieved by using a high-resolution 1024 x 1024 image matrix [3,4]. With the unit described, it has been possible to perform complete digital angiography with automated stepping and thus a single administration of contrast medium in the digital, unsubtracted technique. However, additional series are often required in addition to the stepping series in the region of the knee joint and lower leg, especially if only one side can be adequately
angiography (b) in the region of the knee because of rotation movements mask and contrast images.
of the patient between the
54
displayed because of different flow on each side [ 51. DSA has been reported as the optimum examination technique, especially in the lower leg region [6]. Use was therefore made of experimental software to test the possibilities of the DSA with automated stepping. For good subtraction results in an examination with stepping and DSA, the individual components of an x-ray unit must fulfill certain requirements with regard to the reproducibility of the unit movements and collimator positioning, and the constancy of exposure between mask and contrast images. A positioning accuracy of the unit movements of 0.1 mm related to the patient plane is possible with the described system. DSA with automated stepping was possible in all cases examined. Additional series were necessary only because of rotation movements in the region of the knee (n = 4) or with unilateral vascular occlusions due to different flow on each side (n = 3). An essential prerequisite for the success is optimum timing of mask and contrast images. Furthermore, patient movements during the examination time must be prevented by optimum positioning. Conclusion: Peripheral DSA with automated stepping is an optimum substitute for conventional angio-
graphy with stepping. The number of additional series necessary in addition to the stepping series can be reduced to a minimum. It is possible to reduce both the necessary amount of contrast medium and time.
References Fink U, Heywang SH, Mayr B, Berger H. Subtracted versus nonsubtracted digital imaging in peripheral angiography. Eur J Radio1 1989; 9: 236-240. Triller J, Jegge P, Fritschy P, Fuchs WA. Peripheral venous and peripheral arterial digital subtraction angiography in occlusive diseases of the lower extremity. Digit Bilddiagn 1987; 7: 5-14. Hinz A, Langer M, Zwicker C. Arterielle digitale Subtraktionsangiographie der unteren Extremitlt mit hochaufliisender 1024er Bildmatrix. Rontgen Bl 1989; 42: 257-261. Fink U, Berger H, Mayr B, Hahn D, Ktiffer G. Comparison of digital angiography with DSA of peripheral arteries with 1024 x 1024 matrix. Radiology 1988; 169 (Suppl): 317. Fink U, Heywang SH, Berger H, Jenner E, Fischer K. First clinical results with digital peripheral angiography and stepping. Electromedica 1990; 58: 2-7. Neufang KFR, Gross-Fengels W, Beyer D. Bedeutung der Untersuchungstechnik und Bildnachverarbeitung fur die Qualittit der DSA der unteren Extremitat. Digitale Radiographie, Referate und Vortrlge, Schnetztor-Verlag, Konstanz, 1986, S. 221-229.
