European Journal
of Radiology, 10 (1990) 74-83
14
Elsevier
EURRAD
00008
Synthesized image processing in clinical neurosurgery Kenji Kikuchi, Masayoshi
Kowada, Hiroyuki Ogayama, Jinichi Sasanuma Watanabe
and Kazuo
Department of Neurosurgery, Akita University School of Medicine, Akita. Southern Tohoku Research Institute for Neuroscience, Japan
(Received 7 June 1989; revised version received 15 September
Key words: Image processing;
Magnetic resonance
1989; accepted 20 September
Kohriyama,
1989)
imaging; Cerebral angiography
Abstract
In an effort to achieve efficient image management in clinical neurosurgery utilizing a local image filing system (EFPACS, Fuji Electric Co., Ltd), adequate image-processing and display techniques were developed. One is a method whereby the anatomical location of the thalamic and basal ganglion lesions is determined by automatically superimposing these lesions defined by magnetic resonance imaging (MRI) directly onto the Schaltenbrand-Wahren’s human brain atlas. Horizontal, coronal and sagittal MR images are initially obtained based on the intercommissural line and a perpendicular erected on the midcommissural point as the basic reference coordinates. Precise superimposition is accomplished by the use of these reference axes. This imaging technique may offer the potential for help in anatomical identification of small intracranial lesions. Another technique described in the current communication is automated synthesis of two cerebral angiograms. By simply indicating two reference points, nasion and inion, with a cursor on the display screen, two tilms are automatically superimposed and displayed as a single synthesized image, featuring two different vascular phases simultaneously by a positive(vein)-negative(a.rtery) mode. This technique was applied to patients with complete occlusion of the middle cerebral artery with or without sufficient blood flow through collateral circulation and was found useful in evaluating basic hemodynamics on a single angiographic image.
Introduction Widespread application of digital techniques such as computed tomography (CT), magnetic resonance imaging (MRI) and digital subtraction angiography has created demands for picture archiving and communication systems (PACS) with capabilities for efficient image management [ 1,2]. In an effort to achieve efficient image management in clinical neurosurgery with the use of a local image tiling system, we have developed the following two pieces of image-processing software: (a) automatic mapping of small lesions depicted on MR images on the Schaltenbrand-Wahren’s brain atlas; (b) superimposition of two angiographic films to yield a single synthesized image of two different phases simultaneously. As an example of the clinical Address for reprints: Kenji Neurosurgery, Akita University Akita 010, Japan. 0720-048X/90/$03.50 0
Kikuchi, M.D., Department of School of Medicine, l-l-1 Hondo,
1990 Elsevier Science Publishers
application of these imaging techniques, illustrative cases are presented with small lesions of the thalmus and basal ganglia corresponding to spontaneous hematoma or coagulation following selective thalamotomy, and cases with complete occlusion of the middle cerebral artery. Materials and Methods System architecture A commercially available system for digitization, processing, display and computer storage of film radiographs (EFPACS-500, Fuji Electric Co., Ltd., Japan) was used in the present studies. The major system components include a high resolution film laser scanner, a display system and optical disk storage equipment. In general, film radiographs are scanned and digitized at the maximum matrix of 2048 x 2048 with a range of 10 bits using the high-intensity helium-neon laser scanner, and the digitized images are stored on a
B.V. (Biomedical
Division)
2.6~gigabyte optical disk system. Recorded images are viewed on a high resolution display console as high quality images of 1024 x 1024 pixels with a dynamic range of 8 bits by a 60 Hz non-interlaced scanning mode. Automated localizationof small lesions in the thalamus and basal ganglia on the human brain atlas (a) Digital acquisitionfrom the Schaltenbrand- Wahren’s Brain Atlas. From macroscopic series of sections in the
Atlas [3], 6 horizontal, 5 sagittal and 12 coronal sections were selected and filmed for digital acquisition and storage. Six horizontal sections, made parallel to the intercommissural or anterior commissure-posterior commissure (AC-PC) line, are designated XXXVIII Hd: + 18, + 12, + 7,0, Hv: - 11, - 20. Hd: + 12 and Hv: - 11, for example, indicate horizontal sections 12 mm above and 11 mm below the AC-PC line, respectively. Five sag&al sections, made parallel to the midsagittal line, are designated LXXXV S 1: 0, 4.5, 10.0, 16.0,22.0. Sl: 4.5 indicates the sag&al section 4.5 mm lateral to the midsagittal line. Twelve coronal sections, made parallel to the midcommissural line, are designated XXVII Fa: 29,23, 18, 12, 8, 1, Fp: 3,6, 11, 17, XVI Fa: 7.5,2.5. Fa: 1 and Fp: 3 mean frontal or coronal sections 1 mm anterior and 3 mm posterior to the midcommissural line, respectively. Prior to image processing, the following two reference points were marked on each filmed section for superimposing the MR images on the brain atlas: M,: a midpoint of the AC-PC line and either Ma,,, or Mu,,: a point 10 mm anterior or superior to the midpoint M,. Digital acquisition of these 23 sections was accomplished using the film laser scanner and stored on the optical disk. The same procedure was employed in digital acquisition and storage on the additional microscopic sections specifically magnifying the region of the thalamus and basal ganglia (LXXVIII Hd: + 0.5, Sl: 10.5, LXVIII Fp: 5.0). (b) MR Image acquisition and digitization. For MR
imaging a 0.5-tesla superconductive unit (MRT-SOA, Toshiba, Japan) was used with Tl-weighted (TR 650 ms; TE 40 ms), TZweighted (TR 2000 ms; TE 80 ms) and proton density-weighted (TR 2000 ms; TE 40 ms) sequences obtained in horizontai, sag&al and coronal planes. Initial Tl-weighted midsagittal images defined the anatomy of the third ventricle and the anterior and posterior commissures, and the intercommissural AC-PC line was then identified. Seven serial Tl-weighted horizontal, 5-mm thick sections were obtained based on the intercommissural line seen on the sagittal image so that each section corresponded to a horizontal section of the brain atlas. Coronal and sagit-
tal MR images were also obtained parallel to the midcommissural and the midsagittal lines, respectively (Fig. la). The midcommissural point or the midpoint of the intercommissural line, designated here as M,, was regarded as a zero point for the three coordinates, namely the intercommissural line and two perpendiculars to this basic line. Two of these three coordinates were displayed in centimeter units on each MR image (Fig. lb). Fihn radiographs of these MR images were digitized and the recorded image data were then subjected to image processing for automatic superimposition on the brain atlas. (c) Processingprocedures. The MR image of interest and
the corresponding section of the brain atlas were retrieved from the optical disk (inactive data base) and re-stored in the stock file (active data base). With the relevant section of the atlas on the display screen, the two reference points, M, and either Mar,, or Mulo, were indicated with a cursor. When these reference points marked on the particular slice of the MR image were indicated on the image display, the MR image was automatically enlarged to the size of the atlas. Furthermore, by tracking the outline of the lesion visualized on the enlarged MR image, the lesion was superimposed on the brain atlas with the size precisely corrected (Fig. 2). Automated synthesis of two cerebral angiograms (a) Processing procedures. A plain skull film (termed
base film) and two subtracted cerebral angiograms, on which two reference points for superimposition, nasion (N) and inion (I), had been marked prior to image processing, were digitized at 2048 x 2048 x 10 bits and stored on the optical disk. With a base film present on the display screen, by indicating the bregma (B), tuberculum sellae (TS) and internal occipital proturberance (IP) successively with a cursor, a straight line 9 cm in length was automatically drawn from the IP. A rhomboid was then displayed after accomodating the opposite end of the line to the nearest point on the internal table of the skull On this base film angiogram I could be superimposed automatically, simply by indicating the points N and I on both films. Angiogram II could then be projected upon angiogram I by the same procedure to yield a single synthesized image featuring two different phases simultaneously in a positive (veins)-negative (arteries) mode (Fig. 3). (b) Modijkd Ring’s method. A rhomboid displayed on
the synthesized image consists of two sides of the Twining’s tuberculum sellae-torcular (TIT) line and the tuberculum sellae-bregma (TB) line with a diagonal of
76
the clinoparietal line, and these three lines are drawn from the tuberculum sellae, terminating 2.5 cm inside the inner table of the skull. The clinoparietal line is divided into three parts at the points of one-half and three-quarters with two lines drawn anteriorly parallel to the TTT line and the others drawn downward parallel to the TB line. These divide the lateral surface into three zones of A, B and C, as illustrated in Figure 4. This is a modification of Ring’s topographic method [4], whereby angiographic identification of the terminal branches of the middle cerebral artery is achieved with
the use of a template assigning zones to these branches. In the present study, the template formed in the abovementioned manner was used as an aid to assess the degree of collateral circulation present in cases of middle cerebral artery occlusion. Therefore, with retrograde filling of the middle cerebral artery well visualized in the proximal zone A on the template, the development of collaterals was estimated as excellent. By contrast, evidence of poor collateral circulation was obtained when the retrograde filing was faintly seen in the distal zone C.
Fig. 1. Magnetic resonance (MR) images demonstrating how horizontal (left), coronal (center) and sagittal (right) views are obtained. Each slice is 5 mm in thick either parallel or perpendicular to the intercommissural line (a). The resulting MR images are displayed with two of the three basic reference coordinates in centimeter units (b).
Brain Attar
Angiogram I
Plain Skull Film
Angiogram II
Sel6btion
Enlar~m643t
I Superimpose
@-
Supsrimpo66
I I
Hatching
’@
Manual
Tracking
I
J
I
I
I
I
Fig. 3. Flow-chart of image processing procedure for superimposing two cerebral angiograms. N, nasion; I, inion; B, bregma; TS; tuberculum sellae; IP, internal occipital protuberance. Optical Diik
Fig. 2. Flow-chart of image processing procedure for superimposing MRI lesions on the Schaltenbrand-Wahren’s brain atlas. M,, a midpoint of the intercommissural line. Ma,,,: a point 10 mm anterior to the midpoint M,.
Representative cases Case 1 A 64-year-old woman presented with left hemiparesis. CT showed a small intracerebral hematoma in the right thalamus. On MRI (Fig. lb), a small area of increased signal intensity in the thalamus consistent on the with a hematoma was superimposed Schaltenbrand-Wahren’s brain atlas (Fig. 5). The intracerebral hematoma was identified on the horizontal section in the intercommissural plane to be localized at the pulvinar in the posterolateral portion of the thalamus with an extention to the posterior limb of the internal capsule (Fig. 5a). On the coronal section, 10 mm, posterior to the midcommissural point, the hematoma was seen involving not only nuclei ventralis posterior medialis et lateralis, but also nucleus centrum medianum (Fig. 5b). After conservative therapy the left hemisensory deficit remained, despite marked improve-
I
,5cm
g
Fig. 4. Schematic presentation of the template formed according to a modification of the Ring’s topographic method. With retrograde filling of the middle cerebral artery visualized involving a zone of A, B, or Con the template, the development ofthe collateral circulation is estimated as excellent, moderate, or poor, respectively.
Fig. 5. Brain atlas image with horizontal (a), coronal(b) and sagittal (c) sections after image processing of superimposing the right thalamic hematoma in case 1. The shaded area indicates localization of the hematoma.
ment of the hemiparesis. It was assumed that pressure on the internal capsule by the hematoma eventually resolved, while direct involvement of the sensory nuclei in the thalamus remained unchanged.
Case 2 A 58-year-old man complained of right lower limb motor weakness and was found to have a right hemiparesis and dysarthria. CT revealed an intra-
Fig. 6. MRI (left) and image-processed brain atlas (center and right) in case 2. A right putaminal hematoma is superimposed (center) and an old hematoma involving the left putamen is also well delineated (right).
on the atlas
19
in the thalamus, which had been created by radiofrequency heat coagulation. Irregular high-intensity areas were also seen around this smah lesion, suggesting the presence of cerebral edema after heat coagulation. The MR images, however, failed to identify the precise anatomical localization of the target lesion (Fig. 7). These MR image data were then subjected to image processing for automatic superimposition on the brain atlas, and the heat-coagulated thalamic lesion was found localized precisely at the ventral intermediate nucleus (Fig. 8). This technique was able to provide critical assistance in precise localization of small lesions involving the thalamus and basal ganglia, since in several instances neither CT nor even MRI was sufficient to provide any clues as to the localization.
Fig. 7. MRI with horizontal (upper left), coronal (upper right) and sagittal (lower) views in case 3, showing a small lesion 10 days after stereotaxic nucleus ventralis intermedius thalamotomy.
cerebral hematoma in the left putamen. Automatic superimposition of the MRI-defined lesion on the brain atlas demonstrated a localized hematoma involving the right putamen, claustrum and external capsule, without direct involvement of the internal capsule (Fig. 6, left and center). In addition, axial Tl-weighted images incidentally defined an area of decreased signal intensity in the contralateral putamen consistent with a prior hemorrhage (Fig. 6, left). This lesion was also precisely delineated on the left putamen of the atlas (Fig. 6, right). Medical treatment cured the neurologic symptoms and the absence of direct extension to the internal capsule as evidenced by the synthesized image reflected a good prognosis in terms of neurologic sequelae. Case 3 A 65-year-old women was referred for surgical treatment of left-sided tremor and rigidity after 1 year of medical treatment. Stereotaxic ventrolateral thalamotomy was performed with the target site being the ventral intermediate nucleus. The tremor was abolished instantaneously, and the tonus of the left limb was markedly reduced. MR proton images obtained 10 days after surgery demonstated a 5 mm low-intensity spheroid lesion
Case 4 A 70-year-old man presented with right hemiparesis and dysarthria. In the arterial phase, cerebral angiography demonstrated occlusion of the left middle cerebral artery at the horizontal portion (Fig. 9a). The leptomeningeal collaterals from the anterior cerebral artery were well visualized in the capillary phase and extended to the area supplied by the middle cerebral artery ordinally (Fig. 9b). A single synthesized image was made, composed of two subtracted angiograms of both the arterial and capillary phases, which were obtained 2.2 and 5.8 s, respectively, after injection of contrast material. Retrograde filling of the middle cerebral artery was seen as a positive image involving the A zone of the insular segment, which was in sharp contrast to the negative image of other cerebral vessels (Fig. 9C). Follow-up CT disclosed a localized hypodense lesion involving the left putamen and the head of the caudate nucleus, which may be attributable to the presence of sufIicient blood flow through collateral circulation. Case 5
A 79-year-old woman suddenly developed motor weakness of the left extremities and neurological examination on admission revealed left hemiparesis and conjugate deviation to the right. Atrial fibrillation was shown by an electrocardiogram. Retrograde brachial angiography demonstrated occlusion of the right middle cerebral artery at the horizontal portion (Fig. 10a and lob). On the basis of a single image obtained by synthesis of two angiograms of the arterial and venous phases, retrograde filling from the anterior cerebral artery was found involving only the C zone (Fig. 10~). CT performed 5 days after the onset, showed an extensive hypodense area which indicated a highly advanced cerebral edema due to absence of sufficient collateral circulation.
80
Fig. 8. Magnified brain atlas with horizontal (a), coronal (b) and sagittal (c) sections after superimposing a small coagulated lesion in case 3. The lesion, shown here as a shaded area, was found to be localized in the nucleus ventralis intermedius of the thalamus.
81
in case 4 in the arterial (a) and capillary (b) phases and a synthesized angiographicimage (c) obtained by superimposing(a) and (b). Retrograde fillingof the middle cerebral artery is clearly shown by the positive (black) mode in contrast to arteries depicted by the negative (white) mode.
Fig. 9. Left carotid angiograms
Fig. 10. Right retrograde brachial angiograms in case 5 in the arterial (a) and venous (b) phases and a synthesized angiographic image (c) automatically produced by superimposing (a) and (b). The leptomeningeal collaterals from the anterior cerebral artery are faintly visualized in a distal zone of c defined by the modified Ring’s method.
Discussion PACS in Japan has mainly developed as stand-alone local image filing systems, rather than as integrated parts of total hospital information and image management systems [ 21. When an image filing system is imple-
mented and used as an image workstation, one of the basic issues is how active data or contributory key films should be selected, processed and utilized for efficient medical image management. With the use of Fuji’s EFPACS-500 we have developed two image-processing softwares of our own: (a) automatic superimpo-
82
sition of MRI lesions on the Schaltenbrand-Wahren’s brain atlas for precise anatomical identification; (b) display of a single angiographic image obtained by superimposing two conventional cerebral angiograms with characteristic features of two different vascular phases. Since the use of CT for evaluating intracranial structures has proved to be a highly useful and accurate non-invasive diagnostic tool, several attempts have been made to identify anatomical localization of intracranial lesions more precisely by superimposing CT images directly onto human brain atlases [ 5,6]. One of the fundamental issues involving the overlapping procedure concerns the reference coordinates to be utilized for relating CT sections to the corresponding sections of the brain atlases. In general, conventional axial CT images are obtained on the basis of relationships to lines connecting extracranial reference landmarks such as an orbitomeatal line, a canthomeatal line and a Reid’s base line. Obviously, lines joining intracranial landmarks such as the anterior and posterior commissures are not usually feasible as the basic reference for acquisition of CT images. In contrast to CT scanning, however, MRI is a relatively new diagnostic modality that can generate images of sections of the body obtained in any plane. In the present study, therefore, MRI rather than CT was used to define the anatomy of the third ventricle and the anterior and posterior commissures on the midsagittal image, so that MR images could be successfully obtained based on the intercommissural AC-PC line. As is well known, the AC-PC line and a perpendicular erected on the midpoint between the two commissures are the most important basic reference axes used in the Schaltenbrand-Wahren’s brain atlas [3]. With the use of these MRI techniques, it is feasible to superimpose intracranial lesions depicted on the MR images directly on the Schaltenbrand-Wahren’s brain atlas. However, there are a few problems to be considered for clinical application of this imaging technique. (1) The availability of this automated imaging and amalgamation of MR images with sections of the brain atlas is confined to cases with relatively small lesions in which excessive shift, deformity and/or dilatation of the ventricles are not manifested; (2) individual differences do exist in brain structures which may hamper immediate superimposition; and (3) sections of the Schaltenbrand-Warhen’s brain atlas are not produced in equal thickness, so that slices of MR images do not strictly correspond to sections of the atlas. With these limitations of clinical application in mind, the current imaging techniques may offer an aid in anatomical localization of small lesions localized in the thalamus and basal ganglia. The second method focusses on automatic super-
imposition of two conventional angiographic films to yield a single synthesized image featuring two different vascular phases simultaneously. Iwabuchi et al. [7,8] previously documented two techniques of simultaneous visualization of arterial and venous phases in a single film at carotid angiography. One method, termed simultaneous two-phase angiography [7], is employed by a single exposure of the fnm following two injections of the contrast material at an adequate interval. Another alternative method is called two-phase angiopolygraphy [ 81, in which a film is exposed twice at a certain interval after a single injection of the contrast material. Two disadvantages of these techniques are the complexity of the procedures involving multiple injections and exposures, and the dficulty with which to interpret the images full of arteries and veins. The present method of angiographic synthesis is fully automated and offers the advantage of allowing simultaneous display of the arterial and venous phases with good quality, thus facilitating their easy distinction. In addition, we have modified Ring’s method [4] and developed a new classification as a series of synthetic landmarks automatically displayed on superimposed angiographic images. This is of particular value in quantitative evaluation of the collateral circulation in cases of middle cerebral artery occlusions. In the present report a technique of automated superimposition of two angiographic films was applied to patients with complete occlusion of the middle cerebral artery. It may also provide usefulness in evaluating basic hemodynamics in patients with brain tumors and low-flow arteriovenous malformations, since it can offer simultaneous displays of tumor vessels and stains in the former and those of feeding arteries and draining veins in the latter. Acknowledgments We would like to express our sincere gratitude to Mr. Yasunori Tsuchiya and Mr. Minoru Mukasa of Fuji Electric Co., Ltd., Tokyo, Japan, for their invaluable technical assistance. References 1 Huang HK, Mankovich NJ, Cho PS, Taira R, Stewart B, Ho BK. PACS at UCLA - A status report. J Med Imag Techn 1986; 4: 69-93. 2 Huang HK, Mankovich NJ, Cho PS, Taira R, Stewart BK, Ho BK. Picture archiving and communication systems in Japan. AJR 1987; 48: 427-429. 3 Schahenbrand G, Wahren W. The atlas for stereotaxy of the human brain. Georg Thieme Publishers: Stuttgart, 1977. 4 Ring BA. Angiographic recognition of occlusions of isolated branches of the middle cerebral artery. AJR 1963; 89: 391-397.
83 5 Iseki H, Amano K, Notani, M et al. Anatomical identification of horizontal sections on computed tomogram utilizing Schaltenbrand and Bailey’s atlas of the human brain. Neurol Surg (Tokyo) 1980; 8: 943-949. 6 Birg W, Mundinger F. Direct target point determination for stereotactic brain operations from CT data and the calculation of
setting parameters for polar-coordinate stereotactic device. Appl Neurophysiol 1982; 45: 387-395. 7 Iwabuchi T, Ito Z, Suzuki J. A technique of simultaneous two phase carotid angiography. AJR 1967; 101: 116-120. 8 Iwabuchi T, Sato S, Ouchi H, Nakamichi G. A technique of two carotid angiopolygraphy. Clin Radio1 1969; 20: 198-203.
of Radiology, 10 (1990) 74-83
14
Elsevier
EURRAD
00008
Synthesized image processing in clinical neurosurgery Kenji Kikuchi, Masayoshi
Kowada, Hiroyuki Ogayama, Jinichi Sasanuma Watanabe
and Kazuo
Department of Neurosurgery, Akita University School of Medicine, Akita. Southern Tohoku Research Institute for Neuroscience, Japan
(Received 7 June 1989; revised version received 15 September
Key words: Image processing;
Magnetic resonance
1989; accepted 20 September
Kohriyama,
1989)
imaging; Cerebral angiography
Abstract
In an effort to achieve efficient image management in clinical neurosurgery utilizing a local image filing system (EFPACS, Fuji Electric Co., Ltd), adequate image-processing and display techniques were developed. One is a method whereby the anatomical location of the thalamic and basal ganglion lesions is determined by automatically superimposing these lesions defined by magnetic resonance imaging (MRI) directly onto the Schaltenbrand-Wahren’s human brain atlas. Horizontal, coronal and sagittal MR images are initially obtained based on the intercommissural line and a perpendicular erected on the midcommissural point as the basic reference coordinates. Precise superimposition is accomplished by the use of these reference axes. This imaging technique may offer the potential for help in anatomical identification of small intracranial lesions. Another technique described in the current communication is automated synthesis of two cerebral angiograms. By simply indicating two reference points, nasion and inion, with a cursor on the display screen, two tilms are automatically superimposed and displayed as a single synthesized image, featuring two different vascular phases simultaneously by a positive(vein)-negative(a.rtery) mode. This technique was applied to patients with complete occlusion of the middle cerebral artery with or without sufficient blood flow through collateral circulation and was found useful in evaluating basic hemodynamics on a single angiographic image.
Introduction Widespread application of digital techniques such as computed tomography (CT), magnetic resonance imaging (MRI) and digital subtraction angiography has created demands for picture archiving and communication systems (PACS) with capabilities for efficient image management [ 1,2]. In an effort to achieve efficient image management in clinical neurosurgery with the use of a local image tiling system, we have developed the following two pieces of image-processing software: (a) automatic mapping of small lesions depicted on MR images on the Schaltenbrand-Wahren’s brain atlas; (b) superimposition of two angiographic films to yield a single synthesized image of two different phases simultaneously. As an example of the clinical Address for reprints: Kenji Neurosurgery, Akita University Akita 010, Japan. 0720-048X/90/$03.50 0
Kikuchi, M.D., Department of School of Medicine, l-l-1 Hondo,
1990 Elsevier Science Publishers
application of these imaging techniques, illustrative cases are presented with small lesions of the thalmus and basal ganglia corresponding to spontaneous hematoma or coagulation following selective thalamotomy, and cases with complete occlusion of the middle cerebral artery. Materials and Methods System architecture A commercially available system for digitization, processing, display and computer storage of film radiographs (EFPACS-500, Fuji Electric Co., Ltd., Japan) was used in the present studies. The major system components include a high resolution film laser scanner, a display system and optical disk storage equipment. In general, film radiographs are scanned and digitized at the maximum matrix of 2048 x 2048 with a range of 10 bits using the high-intensity helium-neon laser scanner, and the digitized images are stored on a
B.V. (Biomedical
Division)
2.6~gigabyte optical disk system. Recorded images are viewed on a high resolution display console as high quality images of 1024 x 1024 pixels with a dynamic range of 8 bits by a 60 Hz non-interlaced scanning mode. Automated localizationof small lesions in the thalamus and basal ganglia on the human brain atlas (a) Digital acquisitionfrom the Schaltenbrand- Wahren’s Brain Atlas. From macroscopic series of sections in the
Atlas [3], 6 horizontal, 5 sagittal and 12 coronal sections were selected and filmed for digital acquisition and storage. Six horizontal sections, made parallel to the intercommissural or anterior commissure-posterior commissure (AC-PC) line, are designated XXXVIII Hd: + 18, + 12, + 7,0, Hv: - 11, - 20. Hd: + 12 and Hv: - 11, for example, indicate horizontal sections 12 mm above and 11 mm below the AC-PC line, respectively. Five sag&al sections, made parallel to the midsagittal line, are designated LXXXV S 1: 0, 4.5, 10.0, 16.0,22.0. Sl: 4.5 indicates the sag&al section 4.5 mm lateral to the midsagittal line. Twelve coronal sections, made parallel to the midcommissural line, are designated XXVII Fa: 29,23, 18, 12, 8, 1, Fp: 3,6, 11, 17, XVI Fa: 7.5,2.5. Fa: 1 and Fp: 3 mean frontal or coronal sections 1 mm anterior and 3 mm posterior to the midcommissural line, respectively. Prior to image processing, the following two reference points were marked on each filmed section for superimposing the MR images on the brain atlas: M,: a midpoint of the AC-PC line and either Ma,,, or Mu,,: a point 10 mm anterior or superior to the midpoint M,. Digital acquisition of these 23 sections was accomplished using the film laser scanner and stored on the optical disk. The same procedure was employed in digital acquisition and storage on the additional microscopic sections specifically magnifying the region of the thalamus and basal ganglia (LXXVIII Hd: + 0.5, Sl: 10.5, LXVIII Fp: 5.0). (b) MR Image acquisition and digitization. For MR
imaging a 0.5-tesla superconductive unit (MRT-SOA, Toshiba, Japan) was used with Tl-weighted (TR 650 ms; TE 40 ms), TZweighted (TR 2000 ms; TE 80 ms) and proton density-weighted (TR 2000 ms; TE 40 ms) sequences obtained in horizontai, sag&al and coronal planes. Initial Tl-weighted midsagittal images defined the anatomy of the third ventricle and the anterior and posterior commissures, and the intercommissural AC-PC line was then identified. Seven serial Tl-weighted horizontal, 5-mm thick sections were obtained based on the intercommissural line seen on the sagittal image so that each section corresponded to a horizontal section of the brain atlas. Coronal and sagit-
tal MR images were also obtained parallel to the midcommissural and the midsagittal lines, respectively (Fig. la). The midcommissural point or the midpoint of the intercommissural line, designated here as M,, was regarded as a zero point for the three coordinates, namely the intercommissural line and two perpendiculars to this basic line. Two of these three coordinates were displayed in centimeter units on each MR image (Fig. lb). Fihn radiographs of these MR images were digitized and the recorded image data were then subjected to image processing for automatic superimposition on the brain atlas. (c) Processingprocedures. The MR image of interest and
the corresponding section of the brain atlas were retrieved from the optical disk (inactive data base) and re-stored in the stock file (active data base). With the relevant section of the atlas on the display screen, the two reference points, M, and either Mar,, or Mulo, were indicated with a cursor. When these reference points marked on the particular slice of the MR image were indicated on the image display, the MR image was automatically enlarged to the size of the atlas. Furthermore, by tracking the outline of the lesion visualized on the enlarged MR image, the lesion was superimposed on the brain atlas with the size precisely corrected (Fig. 2). Automated synthesis of two cerebral angiograms (a) Processing procedures. A plain skull film (termed
base film) and two subtracted cerebral angiograms, on which two reference points for superimposition, nasion (N) and inion (I), had been marked prior to image processing, were digitized at 2048 x 2048 x 10 bits and stored on the optical disk. With a base film present on the display screen, by indicating the bregma (B), tuberculum sellae (TS) and internal occipital proturberance (IP) successively with a cursor, a straight line 9 cm in length was automatically drawn from the IP. A rhomboid was then displayed after accomodating the opposite end of the line to the nearest point on the internal table of the skull On this base film angiogram I could be superimposed automatically, simply by indicating the points N and I on both films. Angiogram II could then be projected upon angiogram I by the same procedure to yield a single synthesized image featuring two different phases simultaneously in a positive (veins)-negative (arteries) mode (Fig. 3). (b) Modijkd Ring’s method. A rhomboid displayed on
the synthesized image consists of two sides of the Twining’s tuberculum sellae-torcular (TIT) line and the tuberculum sellae-bregma (TB) line with a diagonal of
76
the clinoparietal line, and these three lines are drawn from the tuberculum sellae, terminating 2.5 cm inside the inner table of the skull. The clinoparietal line is divided into three parts at the points of one-half and three-quarters with two lines drawn anteriorly parallel to the TTT line and the others drawn downward parallel to the TB line. These divide the lateral surface into three zones of A, B and C, as illustrated in Figure 4. This is a modification of Ring’s topographic method [4], whereby angiographic identification of the terminal branches of the middle cerebral artery is achieved with
the use of a template assigning zones to these branches. In the present study, the template formed in the abovementioned manner was used as an aid to assess the degree of collateral circulation present in cases of middle cerebral artery occlusion. Therefore, with retrograde filling of the middle cerebral artery well visualized in the proximal zone A on the template, the development of collaterals was estimated as excellent. By contrast, evidence of poor collateral circulation was obtained when the retrograde filing was faintly seen in the distal zone C.
Fig. 1. Magnetic resonance (MR) images demonstrating how horizontal (left), coronal (center) and sagittal (right) views are obtained. Each slice is 5 mm in thick either parallel or perpendicular to the intercommissural line (a). The resulting MR images are displayed with two of the three basic reference coordinates in centimeter units (b).
Brain Attar
Angiogram I
Plain Skull Film
Angiogram II
Sel6btion
Enlar~m643t
I Superimpose
@-
Supsrimpo66
I I
Hatching
’@
Manual
Tracking
I
J
I
I
I
I
Fig. 3. Flow-chart of image processing procedure for superimposing two cerebral angiograms. N, nasion; I, inion; B, bregma; TS; tuberculum sellae; IP, internal occipital protuberance. Optical Diik
Fig. 2. Flow-chart of image processing procedure for superimposing MRI lesions on the Schaltenbrand-Wahren’s brain atlas. M,, a midpoint of the intercommissural line. Ma,,,: a point 10 mm anterior to the midpoint M,.
Representative cases Case 1 A 64-year-old woman presented with left hemiparesis. CT showed a small intracerebral hematoma in the right thalamus. On MRI (Fig. lb), a small area of increased signal intensity in the thalamus consistent on the with a hematoma was superimposed Schaltenbrand-Wahren’s brain atlas (Fig. 5). The intracerebral hematoma was identified on the horizontal section in the intercommissural plane to be localized at the pulvinar in the posterolateral portion of the thalamus with an extention to the posterior limb of the internal capsule (Fig. 5a). On the coronal section, 10 mm, posterior to the midcommissural point, the hematoma was seen involving not only nuclei ventralis posterior medialis et lateralis, but also nucleus centrum medianum (Fig. 5b). After conservative therapy the left hemisensory deficit remained, despite marked improve-
I
,5cm
g
Fig. 4. Schematic presentation of the template formed according to a modification of the Ring’s topographic method. With retrograde filling of the middle cerebral artery visualized involving a zone of A, B, or Con the template, the development ofthe collateral circulation is estimated as excellent, moderate, or poor, respectively.
Fig. 5. Brain atlas image with horizontal (a), coronal(b) and sagittal (c) sections after image processing of superimposing the right thalamic hematoma in case 1. The shaded area indicates localization of the hematoma.
ment of the hemiparesis. It was assumed that pressure on the internal capsule by the hematoma eventually resolved, while direct involvement of the sensory nuclei in the thalamus remained unchanged.
Case 2 A 58-year-old man complained of right lower limb motor weakness and was found to have a right hemiparesis and dysarthria. CT revealed an intra-
Fig. 6. MRI (left) and image-processed brain atlas (center and right) in case 2. A right putaminal hematoma is superimposed (center) and an old hematoma involving the left putamen is also well delineated (right).
on the atlas
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in the thalamus, which had been created by radiofrequency heat coagulation. Irregular high-intensity areas were also seen around this smah lesion, suggesting the presence of cerebral edema after heat coagulation. The MR images, however, failed to identify the precise anatomical localization of the target lesion (Fig. 7). These MR image data were then subjected to image processing for automatic superimposition on the brain atlas, and the heat-coagulated thalamic lesion was found localized precisely at the ventral intermediate nucleus (Fig. 8). This technique was able to provide critical assistance in precise localization of small lesions involving the thalamus and basal ganglia, since in several instances neither CT nor even MRI was sufficient to provide any clues as to the localization.
Fig. 7. MRI with horizontal (upper left), coronal (upper right) and sagittal (lower) views in case 3, showing a small lesion 10 days after stereotaxic nucleus ventralis intermedius thalamotomy.
cerebral hematoma in the left putamen. Automatic superimposition of the MRI-defined lesion on the brain atlas demonstrated a localized hematoma involving the right putamen, claustrum and external capsule, without direct involvement of the internal capsule (Fig. 6, left and center). In addition, axial Tl-weighted images incidentally defined an area of decreased signal intensity in the contralateral putamen consistent with a prior hemorrhage (Fig. 6, left). This lesion was also precisely delineated on the left putamen of the atlas (Fig. 6, right). Medical treatment cured the neurologic symptoms and the absence of direct extension to the internal capsule as evidenced by the synthesized image reflected a good prognosis in terms of neurologic sequelae. Case 3 A 65-year-old women was referred for surgical treatment of left-sided tremor and rigidity after 1 year of medical treatment. Stereotaxic ventrolateral thalamotomy was performed with the target site being the ventral intermediate nucleus. The tremor was abolished instantaneously, and the tonus of the left limb was markedly reduced. MR proton images obtained 10 days after surgery demonstated a 5 mm low-intensity spheroid lesion
Case 4 A 70-year-old man presented with right hemiparesis and dysarthria. In the arterial phase, cerebral angiography demonstrated occlusion of the left middle cerebral artery at the horizontal portion (Fig. 9a). The leptomeningeal collaterals from the anterior cerebral artery were well visualized in the capillary phase and extended to the area supplied by the middle cerebral artery ordinally (Fig. 9b). A single synthesized image was made, composed of two subtracted angiograms of both the arterial and capillary phases, which were obtained 2.2 and 5.8 s, respectively, after injection of contrast material. Retrograde filling of the middle cerebral artery was seen as a positive image involving the A zone of the insular segment, which was in sharp contrast to the negative image of other cerebral vessels (Fig. 9C). Follow-up CT disclosed a localized hypodense lesion involving the left putamen and the head of the caudate nucleus, which may be attributable to the presence of sufIicient blood flow through collateral circulation. Case 5
A 79-year-old woman suddenly developed motor weakness of the left extremities and neurological examination on admission revealed left hemiparesis and conjugate deviation to the right. Atrial fibrillation was shown by an electrocardiogram. Retrograde brachial angiography demonstrated occlusion of the right middle cerebral artery at the horizontal portion (Fig. 10a and lob). On the basis of a single image obtained by synthesis of two angiograms of the arterial and venous phases, retrograde filling from the anterior cerebral artery was found involving only the C zone (Fig. 10~). CT performed 5 days after the onset, showed an extensive hypodense area which indicated a highly advanced cerebral edema due to absence of sufficient collateral circulation.
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Fig. 8. Magnified brain atlas with horizontal (a), coronal (b) and sagittal (c) sections after superimposing a small coagulated lesion in case 3. The lesion, shown here as a shaded area, was found to be localized in the nucleus ventralis intermedius of the thalamus.
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in case 4 in the arterial (a) and capillary (b) phases and a synthesized angiographicimage (c) obtained by superimposing(a) and (b). Retrograde fillingof the middle cerebral artery is clearly shown by the positive (black) mode in contrast to arteries depicted by the negative (white) mode.
Fig. 9. Left carotid angiograms
Fig. 10. Right retrograde brachial angiograms in case 5 in the arterial (a) and venous (b) phases and a synthesized angiographic image (c) automatically produced by superimposing (a) and (b). The leptomeningeal collaterals from the anterior cerebral artery are faintly visualized in a distal zone of c defined by the modified Ring’s method.
Discussion PACS in Japan has mainly developed as stand-alone local image filing systems, rather than as integrated parts of total hospital information and image management systems [ 21. When an image filing system is imple-
mented and used as an image workstation, one of the basic issues is how active data or contributory key films should be selected, processed and utilized for efficient medical image management. With the use of Fuji’s EFPACS-500 we have developed two image-processing softwares of our own: (a) automatic superimpo-
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sition of MRI lesions on the Schaltenbrand-Wahren’s brain atlas for precise anatomical identification; (b) display of a single angiographic image obtained by superimposing two conventional cerebral angiograms with characteristic features of two different vascular phases. Since the use of CT for evaluating intracranial structures has proved to be a highly useful and accurate non-invasive diagnostic tool, several attempts have been made to identify anatomical localization of intracranial lesions more precisely by superimposing CT images directly onto human brain atlases [ 5,6]. One of the fundamental issues involving the overlapping procedure concerns the reference coordinates to be utilized for relating CT sections to the corresponding sections of the brain atlases. In general, conventional axial CT images are obtained on the basis of relationships to lines connecting extracranial reference landmarks such as an orbitomeatal line, a canthomeatal line and a Reid’s base line. Obviously, lines joining intracranial landmarks such as the anterior and posterior commissures are not usually feasible as the basic reference for acquisition of CT images. In contrast to CT scanning, however, MRI is a relatively new diagnostic modality that can generate images of sections of the body obtained in any plane. In the present study, therefore, MRI rather than CT was used to define the anatomy of the third ventricle and the anterior and posterior commissures on the midsagittal image, so that MR images could be successfully obtained based on the intercommissural AC-PC line. As is well known, the AC-PC line and a perpendicular erected on the midpoint between the two commissures are the most important basic reference axes used in the Schaltenbrand-Wahren’s brain atlas [3]. With the use of these MRI techniques, it is feasible to superimpose intracranial lesions depicted on the MR images directly on the Schaltenbrand-Wahren’s brain atlas. However, there are a few problems to be considered for clinical application of this imaging technique. (1) The availability of this automated imaging and amalgamation of MR images with sections of the brain atlas is confined to cases with relatively small lesions in which excessive shift, deformity and/or dilatation of the ventricles are not manifested; (2) individual differences do exist in brain structures which may hamper immediate superimposition; and (3) sections of the Schaltenbrand-Warhen’s brain atlas are not produced in equal thickness, so that slices of MR images do not strictly correspond to sections of the atlas. With these limitations of clinical application in mind, the current imaging techniques may offer an aid in anatomical localization of small lesions localized in the thalamus and basal ganglia. The second method focusses on automatic super-
imposition of two conventional angiographic films to yield a single synthesized image featuring two different vascular phases simultaneously. Iwabuchi et al. [7,8] previously documented two techniques of simultaneous visualization of arterial and venous phases in a single film at carotid angiography. One method, termed simultaneous two-phase angiography [7], is employed by a single exposure of the fnm following two injections of the contrast material at an adequate interval. Another alternative method is called two-phase angiopolygraphy [ 81, in which a film is exposed twice at a certain interval after a single injection of the contrast material. Two disadvantages of these techniques are the complexity of the procedures involving multiple injections and exposures, and the dficulty with which to interpret the images full of arteries and veins. The present method of angiographic synthesis is fully automated and offers the advantage of allowing simultaneous display of the arterial and venous phases with good quality, thus facilitating their easy distinction. In addition, we have modified Ring’s method [4] and developed a new classification as a series of synthetic landmarks automatically displayed on superimposed angiographic images. This is of particular value in quantitative evaluation of the collateral circulation in cases of middle cerebral artery occlusions. In the present report a technique of automated superimposition of two angiographic films was applied to patients with complete occlusion of the middle cerebral artery. It may also provide usefulness in evaluating basic hemodynamics in patients with brain tumors and low-flow arteriovenous malformations, since it can offer simultaneous displays of tumor vessels and stains in the former and those of feeding arteries and draining veins in the latter. Acknowledgments We would like to express our sincere gratitude to Mr. Yasunori Tsuchiya and Mr. Minoru Mukasa of Fuji Electric Co., Ltd., Tokyo, Japan, for their invaluable technical assistance. References 1 Huang HK, Mankovich NJ, Cho PS, Taira R, Stewart B, Ho BK. PACS at UCLA - A status report. J Med Imag Techn 1986; 4: 69-93. 2 Huang HK, Mankovich NJ, Cho PS, Taira R, Stewart BK, Ho BK. Picture archiving and communication systems in Japan. AJR 1987; 48: 427-429. 3 Schahenbrand G, Wahren W. The atlas for stereotaxy of the human brain. Georg Thieme Publishers: Stuttgart, 1977. 4 Ring BA. Angiographic recognition of occlusions of isolated branches of the middle cerebral artery. AJR 1963; 89: 391-397.
83 5 Iseki H, Amano K, Notani, M et al. Anatomical identification of horizontal sections on computed tomogram utilizing Schaltenbrand and Bailey’s atlas of the human brain. Neurol Surg (Tokyo) 1980; 8: 943-949. 6 Birg W, Mundinger F. Direct target point determination for stereotactic brain operations from CT data and the calculation of
setting parameters for polar-coordinate stereotactic device. Appl Neurophysiol 1982; 45: 387-395. 7 Iwabuchi T, Ito Z, Suzuki J. A technique of simultaneous two phase carotid angiography. AJR 1967; 101: 116-120. 8 Iwabuchi T, Sato S, Ouchi H, Nakamichi G. A technique of two carotid angiopolygraphy. Clin Radio1 1969; 20: 198-203.
