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CT scanning of the breast using a conventional CT scanner
CT Scanning of the Breast Using a Conventional CT Scanner METHOD
Bruce D. Doust, M.D. John R. Milbrath, M.D. Vivienne L. Doust, M.B. Department of Radiology, Medical College of Wisconsin, Milwaukee, Wisconsin, and Veterans Administration Medical Center, Wood, Wisconsin Using a conventional body CT scanner, computed tomography of the breast was performed on 32 patients known to have or suspected of having breast masses. Xeromammograms were available for comparison in all cases. All mass lesions were histologically proved. Seven patients were examined prone, 25 supine. The prone position yielded pictures that resembled craniocaudal mammograms. Breast asymmetry, skin thickening, stranding from a mass to the chest wall, calcification, and axillary lymphadenopathy could be demonstrated by means of CT. The portion of the breast adjacent to the chest wall was more readily examined by means of CT than by conventional mammography. Internal mammary nodes could not be demonstrated.
Hitherto, computed tomography of the breast has been performed only at the few centers possessing a dedicated CT breast scanner (l-5). If breast CT is to be economically feasible, a means of examining the breast on more widely available conventional body CT scanners is needed. This study was undertaken in order to determine the feasibility of performing breast CT on a conventional body scanner, to determine the optimal technique of examination, to obtain some preliminary indication of the appearances of the normal breast and of breast masses, and to determine whether axillary and internal mammary lymphadenopathy could be demonstrated. Presented at the sixty-sixth Scientific Assembly Meeting of the Radiological Society Texas, November 16-21, 1980. Address
reprint
requests
of North
to Bruce D. Doust,
ment of Radiology, Veterans Administration 53193.
Doust et al. _-_
296
and Annual America, Dallas,
M.D., DepartHospital, Wood, WI
AND MATERIALS
All examinations were performed on a commercially available body CT scanner (GE CTT 8800). Two groups of patients were examined. Group 1 consisted of 7 patients whose xeromammograms were positive for carcinoma and who were examined immediately prior to mastectomy. Group 2 consisted of 25 patients with carcinoma of the breast who were examined by CT as part of radiation therapy planning. Patients in Group 1 were examined prone. The pads normally placed on the CT scanner gantry for radiation therapy planning were separated by an interval of approximately 6 inches. The patient lay prone, and the breasts hung into the gap between the pads. The patient’s arms were extended beyond her head. After a preliminary lateral computed radiograph (Figure l), contiguous lo-mm slices were taken throughout the breasts and axillae. In 3 cases the area of the lesion was also examined by means of 5-mm contiguous slices and in 2 cases by means of 1.5-mm contiguous slices. A reconstruction circle large enough to encompass both the thorax and the breasts was used. The 25 patients in Group 2 were examined supine, with the arm on the side of the lesion extended above the head, and the contralateral arm by the patient’s side. In 15 of these patients, only a limited series of slices were taken through the breast, and in 16 cases the patient had undergone mastectomy prior to the study. Again, a large reconstruction circle was used. These studies were used retrospectively to determine the configuration of the tissues within the remaining normal breast. Intravenous contrast agent was not used. The clinical material is summarized in Table 1.
RESULTS
Patient Position The prone position appeared in many ways to be more satisfactory than the supine. In the prone position the CT: the burnal
ot Computed
Tomography,
Copyright
0 University Park Press, 1981 Vol. 5, No. 4, Printed in U.S.A.
Figure 2. Asymmetrical breasts. In the prone position, asymmetry of the breasts can be readily appreciated. There is large carcinoma in the left breast. The right breast is atrophic but normal for the age of the patient (74 years).
Figure 1.
Lateral localizer view of the breasts in a prone patient. The breasts hang in the gap between the pads on which the patient lies.
CT images resembled the craniocaudal view of conventional mammography, and both breasts hung freely from the chest wall. Their shape was relatively independent of minor degrees of patient rotation, and comparison with the contralateral breast was facilitated. Thus asymmetry between the two breasts was readily perceived (Figure 2). Also, in the prone position respiratory motion of the breasts was eliminated even if the patient breathed during the exposure. It was desirable to extend the patient’s arms beyond her head in order to assure symmetry and to obtain images of the axillae. Axillary lymph nodes, being surrounded by fat, were easily demonstrated.
The glandular elements of the breast extended backward and outward from the nipple. In the fatty breast, the glandular elements gradually faded away posteriorly with no clear posterior line of demarcation. In glandular breasts there was a shallow, sharply defined zone of fat, free of glandular elements, lying immediately in front of the pectoral muscles (Figure 3). Laterally and medially, however, the glandular elements approached the pectoral muscles.
Appearances of the Normal Breast The appearances varied depending on the patient’s age and the extent of the glandular elements within the breast (Figures 3-6). Table 1.
Clinical
Carcinoma Patient scanned Patient scanned Fibroadenoma Normal Total
material before mastectomy after mastectomy
18 12 1 1 32
Figure 3. Glandular breasts (patient prone). The glandular tissue contains lacunae of fat (which ap pear black). Posteriorly, against the chest wall, there is a broad-based conical area of fat that is free of glandular elements. Glandular elements approach close to the pectoral musculature medially and laterally. Other slices demonstrated a fibroadenoma elsewhere in the left breast (see Figure 13). CT Scanning
of the Breast 297
Figure
4.
Large normal
fatty
breasts.
Mammary fat was sometimes diffusely intermingled with the glandular or ductal elements (Figures 2, 4) or alternatively appeared as well-defined lacunae within glandular areas (Figure 3). Glandular elements were sometimes quite sparse (Figures 4, 6). The degree of glandularity varied from one part of the breast to another (Figures 4, 5). The deepest part of the breast and the underlying chest wall were better seen with CT than with xerography. In one case a lesion in the deepest part of the breast (a carcinoma) was better seen on CT (Figure 8) than in the craniocaudal mammogram (Figure 9). However, the carcinoma was adequately demonstrated in the mediolateral xeromammogram.
Figure 5. A second slice at a different level in the patient in Figure4. There is considerably more glandular tissue in Figure 5 than in Figure 4. There are also masslike irregularities of the glandular pattern in the left breast, which represent normal glandular tissue. There is symmetrical deformity of both breasts because of contact with the scanning table. Bubbles of air can be seen trapped between the skin of the breast and the gantry.
Doust
298
et al
Figure 6. An atrophic but otherwise normal breast. The patient had a carcinoma in the contralateral breast.
(arrow) is seen immediately Figure 7. A carcinoma adjacent to an area of glandular elements. There is some haziness of its posterior margin. Its attenuation coefficient was not clearly different from that of the adjacent glandular tissue.
Figure 8. Carcinoma (arrow) lying adjacent to the chest wall. The carcinoma is connected to the chest wall by a band of tissue denser than the surrounding fat. There is fine irregularity of the margin of the carcinoma.
Calcification was less clearly demonstrated with CT than with xeromammography. Vascular calcification that was easily seen on the xeromammogram could not be demonstrated by routine CT techniques. Gross calcification (Figures 10, 11) within a tumor as well as skin thickening (Figure 12) were demonstrated by either method.
Figure 9. Craniocaudal xeromammogram of the deep-seated carcinoma seen in Figure 8. The carcinoma (arrow) was almost missed on this view because it was so close to the chest wall.
Figure 10. Calcification in a large carcinoma. The tumor measures over 6 cm in diameter. Calcification can be seen in its deeper part.
The single fibroadenoma in this series (Figure 13) had a sharp outline. Its attenuation coefficient was not clearly different from that of the adjacent glandular tissue. Extramammary
Areas
In this series, there was not a single case of recognizable abnormality of the internal mammary node chain. In one case, abnormality of the mediastinal nodes was recognized.
Figure 11. Xerogram of the patient in Figure 10 shows the extensive calcification in the carcinoma more clearly than does the CT scan.
CT Scanning
of the Breast
Figure 14. Left axillary lymphadenopathy in carcinoma. The involved lymph nodes are quite grossly enlarged. No corresponding masses can be seen in the contralateral axilla. There is a large carcinoma in the left breast. Figure 12. Skin thickening in an extensive carcinoma. In this supine scan the carcinoma is seen as a large mass merging with the skin. The skin thickening is best seen medial to the mass.
Axillary lymph nodes could be identified on the CT scan. Fat is plentiful in the axilla, and the nodes, both normal and abnormal, stood out against it. Gross lymphadenopathy was readily recognized (Figure 14). Asymmetry of the axillae could be best assessed when the patient lay prone with her arms extended above her head. Radiation Dosage
Radiation dosage was measured in 2 patients by means of four thermoluminescent dosimeters applied to the skin of each breast just below the nipple. The results are presented in Table 2. DISCUSSION
The prone position, with the breasts hanging dependent, separated the tissues of the breast from one another, and provided images that were strikingly similar to the craniocaudal mammogram, so that the image was of a form already familiar to many radiologists. It also ensured that both breasts and both axillae were examined under identical conditions, so that asymmetry was readily perceived. There was some difficulty with the prone position in large patients with large breasts because the aperture of the Table 2. Radiation dosage as measured in 2 patients by means of four thermoluminescent dosimeters placed on the skin of each breast Figure 13. Fibroadenoma (same patient as in Figure 3). The fibroadenoma (f) appears as a sharply defined, rounded mass lesion with a smooth margin. The dense glandular tissue behind it contains lacunae of fat. There is a band of fat, which is free of glandular elements, lying against the chest wall-a normal appearance.
Doust et al. 300
Exposure factors Number of slices Radiation dose alncluded
Patient I
Patient II
120 kV, 480 mAs 22a
120 kV, 205 mAs
3.2 R
1.2 R
three sets of slices
through
the lesion.
10
CT scanner was not always big enough to accommodate the patient and still leave enough space for the breasts to hang free. In Figures 4 and 5 the breasts have come into contact with and have been deformed by the bed of the scanning gantry. The supine images may be more satisfactory for localization of lesions prior to excision, because the patient is in the supine position during surgery. However, the configuration of the breast in the supine patient rendered the breast images difficult to compare with each other and with the mammograms. Large breasts occasionally extended beyond the reconstruction circle when the patient was supine. In the absence of intravenous contrast material, it appears that the attenuation coefficient of uncalcified carcinomas is not significantly different from that of normal ductal and glandular elements (Table 3). This result agrees with the observations of others (3, 5). Fine calcification is not well demonstrated by means of CT. The CT voxels are large when compared with the small flecks of calcium seen in some carcinomas, so that partial volume averaging obscures the calcium. This problem is more serious when thick slices are used. Because calcium may be present in both benign and malignant lesions, it is the pattern of calcification rather than its mere presence that differentiates benign from malignant lesions. Therefore, it is unlikely that digital printouts of the attenuation coefficients of individual pixels, as described for lung lesions (6), will prove useful in the diagnosis of breast carcinoma. However, this technique may be helpful in the axilla, to detect metastatic nodes. It has been shown by others (2, 3, 5) that, when intravenous contrast agent is administered, carcinomas increase their attenuation coefficient in a manner that is sufficiently characteristic to improve the diagnostic accuracy of CT. Intravenous contrast agent was not used in this study, primarily for ethical reasons. The slight added hazard of intravenous contrast agent was thought to be unacceptable until this preliminary investigation indicated that CT mamTable 3.
Attenuation Tissue
Mammary
fat
coefficients
of breast No. of readinas
tissues No. of breasts
17
14
Glandular elements Dense breasts Fatty breasts
33 20 13
25 14 11
Uncalcified
30 6 11
carcinoma
Fibroadenoma Pectoral
muscle
mography might offer some benefit to the patient. The radiation dose was measured at the skin surface of the dependent breasts. The dose for a scout view and a single set of contiguous slices is about 1.2 R. The mid-breast dose is likely to be only slightly less than the surface dose, since the breast was irradiated throughout the 360” rotation of the CT x-ray tube during each exposure and the voltage used (120 kV) was considerably higher than that used in conventional film mammography or xeromammography. If this assumption is correct, the mid-breast dose for CT mammography as performed in this series is likely to be higher than that for xeromammography, suggesting that it is not suitable for use as a mass screening tool (7). The spatial resolution of the images is sufficiently good that some of the criteria of malignancy developed for xerography-e.g., skin thickening, irregularity of the outline of a carcinoma (Figure 7), and stranding running from the mass (8)-can be applied to the CT images. The most striking advantage of the technique seems to be the clarity with which that portion of the breast adjacent to the pectoral musculature is displayed. The band of fat in this area in densely glandular breasts acts as a natural contrast agent. It is probable that the presence of material of higher attenuation coefficient than fat in this zone is a sign of malignancy. A disappointing finding was that there was not a single instance, with the patient either prone or supine, in which the internal mammary lymph nodes were visible. Possibly there was not a case in this series in which the nodes were involved, but this hypothesis appears unlikely in light of the advanced disease demonstrated in some patients. Axillary nodes stood out clearly against the axillary fat. The criteria for abnormal axillary nodes cannot be firmly established on the basis of so small a series. However, asymmetry when compared to the contralateral axilla suggests malignant involvement. An increase in the attenuation coefficient of a node (Hounsfield
units) _____Mean attenuation coefficient -135
Highest value
Lowest value
- 123
-169
Mean SD 10
3 22 - 25
50 50 4
- 56 0 - 56
10 19 12
9
6
33
- 20
12
1
23
32
15
7
11
40
63
_
CT
-7
11
Scanning
of the Breast 301
with intravenous contrast, or the recognition of nodal calcification by means of digital printouts of the attenuation coefficients of individual pixels as described for solitary pulmonary nodules (6), may allow more sensitive detection of metastatic axillary nodal involvement in the future.
3.
4.
5. REFERENCES 6. 1.
Chang CH, Sibala JL, Gallagher
2.
tomography of the breast. ology 124:827-829, 1977 Chang CH, Sibala JL, Fritz SL, et al: Computed tomographic evaluation of the breast. AJR 131:459-464, 1978
JH, et al: Computed A preliminary report. Radi-
CONTINUING (CT SCANNING
1.
2.
3.
4.
MEDICAL
EDUCATION
7.
8.
Chang CH, Sibala JL, Fritz SL, et al: Specific value of computed tomographic breast scanner (CT i M) in diagnosis of breast diseases. Radiology 132:647-652, 1979 Chang CH, Sibala JL, Lin F, et al: Preoperative diagnosis of potentially precancerous breast lesions by computed tomography breast scanner: Preliminary study. Radiology 129:209-210, 1978 Gisvold JJ, Karsell PR, Reese DF, McCullough EC: Clinical evaluation of computerised tomographic mammography. Mayo Clin Proc 52:181-185, 1977 Siegelman SS, Zerhouni EA, Leo FP, et al: CT of the solitary pulmonary nodule. AJR 135:1-13, 1980 Muntz EP, Wilkinson E, George FW: Mammography at reduced doses: Present performance and future possibilities. AJR 134:741-747, 1980 Wolf JN: Xeroradiography of the Breast. Charles C Thomas, Springfield, Ill., 1972
QUESTIONS
OF THE BREAST USING A CONVENTIONAL
CT SCANNER)
CT of the breast can demonstrate intramammary calcification as well as xeromammography. a. True b. False At the back of the breast, immediately against the chest wall there is: a. Particularly dense glandular tissue b. A layer of fatty tissue C. A series of prominent lymph nodes In the absence of intravenous contrast, the CT number of uncalcified breast carcinoma is higher than that of glandular tissue in 90% of cases. a. True b. False The radiation dose from breast CT is: a. Higher than b. Lower than C. The same as conventional film screen mammography.
Doust et al. 302
Bruce D. Doust, M.D. John R. Milbrath, M.D. Vivienne L. Doust, M.B. Department of Radiology, Medical College of Wisconsin, Milwaukee, Wisconsin, and Veterans Administration Medical Center, Wood, Wisconsin Using a conventional body CT scanner, computed tomography of the breast was performed on 32 patients known to have or suspected of having breast masses. Xeromammograms were available for comparison in all cases. All mass lesions were histologically proved. Seven patients were examined prone, 25 supine. The prone position yielded pictures that resembled craniocaudal mammograms. Breast asymmetry, skin thickening, stranding from a mass to the chest wall, calcification, and axillary lymphadenopathy could be demonstrated by means of CT. The portion of the breast adjacent to the chest wall was more readily examined by means of CT than by conventional mammography. Internal mammary nodes could not be demonstrated.
Hitherto, computed tomography of the breast has been performed only at the few centers possessing a dedicated CT breast scanner (l-5). If breast CT is to be economically feasible, a means of examining the breast on more widely available conventional body CT scanners is needed. This study was undertaken in order to determine the feasibility of performing breast CT on a conventional body scanner, to determine the optimal technique of examination, to obtain some preliminary indication of the appearances of the normal breast and of breast masses, and to determine whether axillary and internal mammary lymphadenopathy could be demonstrated. Presented at the sixty-sixth Scientific Assembly Meeting of the Radiological Society Texas, November 16-21, 1980. Address
reprint
requests
of North
to Bruce D. Doust,
ment of Radiology, Veterans Administration 53193.
Doust et al. _-_
296
and Annual America, Dallas,
M.D., DepartHospital, Wood, WI
AND MATERIALS
All examinations were performed on a commercially available body CT scanner (GE CTT 8800). Two groups of patients were examined. Group 1 consisted of 7 patients whose xeromammograms were positive for carcinoma and who were examined immediately prior to mastectomy. Group 2 consisted of 25 patients with carcinoma of the breast who were examined by CT as part of radiation therapy planning. Patients in Group 1 were examined prone. The pads normally placed on the CT scanner gantry for radiation therapy planning were separated by an interval of approximately 6 inches. The patient lay prone, and the breasts hung into the gap between the pads. The patient’s arms were extended beyond her head. After a preliminary lateral computed radiograph (Figure l), contiguous lo-mm slices were taken throughout the breasts and axillae. In 3 cases the area of the lesion was also examined by means of 5-mm contiguous slices and in 2 cases by means of 1.5-mm contiguous slices. A reconstruction circle large enough to encompass both the thorax and the breasts was used. The 25 patients in Group 2 were examined supine, with the arm on the side of the lesion extended above the head, and the contralateral arm by the patient’s side. In 15 of these patients, only a limited series of slices were taken through the breast, and in 16 cases the patient had undergone mastectomy prior to the study. Again, a large reconstruction circle was used. These studies were used retrospectively to determine the configuration of the tissues within the remaining normal breast. Intravenous contrast agent was not used. The clinical material is summarized in Table 1.
RESULTS
Patient Position The prone position appeared in many ways to be more satisfactory than the supine. In the prone position the CT: the burnal
ot Computed
Tomography,
Copyright
0 University Park Press, 1981 Vol. 5, No. 4, Printed in U.S.A.
Figure 2. Asymmetrical breasts. In the prone position, asymmetry of the breasts can be readily appreciated. There is large carcinoma in the left breast. The right breast is atrophic but normal for the age of the patient (74 years).
Figure 1.
Lateral localizer view of the breasts in a prone patient. The breasts hang in the gap between the pads on which the patient lies.
CT images resembled the craniocaudal view of conventional mammography, and both breasts hung freely from the chest wall. Their shape was relatively independent of minor degrees of patient rotation, and comparison with the contralateral breast was facilitated. Thus asymmetry between the two breasts was readily perceived (Figure 2). Also, in the prone position respiratory motion of the breasts was eliminated even if the patient breathed during the exposure. It was desirable to extend the patient’s arms beyond her head in order to assure symmetry and to obtain images of the axillae. Axillary lymph nodes, being surrounded by fat, were easily demonstrated.
The glandular elements of the breast extended backward and outward from the nipple. In the fatty breast, the glandular elements gradually faded away posteriorly with no clear posterior line of demarcation. In glandular breasts there was a shallow, sharply defined zone of fat, free of glandular elements, lying immediately in front of the pectoral muscles (Figure 3). Laterally and medially, however, the glandular elements approached the pectoral muscles.
Appearances of the Normal Breast The appearances varied depending on the patient’s age and the extent of the glandular elements within the breast (Figures 3-6). Table 1.
Clinical
Carcinoma Patient scanned Patient scanned Fibroadenoma Normal Total
material before mastectomy after mastectomy
18 12 1 1 32
Figure 3. Glandular breasts (patient prone). The glandular tissue contains lacunae of fat (which ap pear black). Posteriorly, against the chest wall, there is a broad-based conical area of fat that is free of glandular elements. Glandular elements approach close to the pectoral musculature medially and laterally. Other slices demonstrated a fibroadenoma elsewhere in the left breast (see Figure 13). CT Scanning
of the Breast 297
Figure
4.
Large normal
fatty
breasts.
Mammary fat was sometimes diffusely intermingled with the glandular or ductal elements (Figures 2, 4) or alternatively appeared as well-defined lacunae within glandular areas (Figure 3). Glandular elements were sometimes quite sparse (Figures 4, 6). The degree of glandularity varied from one part of the breast to another (Figures 4, 5). The deepest part of the breast and the underlying chest wall were better seen with CT than with xerography. In one case a lesion in the deepest part of the breast (a carcinoma) was better seen on CT (Figure 8) than in the craniocaudal mammogram (Figure 9). However, the carcinoma was adequately demonstrated in the mediolateral xeromammogram.
Figure 5. A second slice at a different level in the patient in Figure4. There is considerably more glandular tissue in Figure 5 than in Figure 4. There are also masslike irregularities of the glandular pattern in the left breast, which represent normal glandular tissue. There is symmetrical deformity of both breasts because of contact with the scanning table. Bubbles of air can be seen trapped between the skin of the breast and the gantry.
Doust
298
et al
Figure 6. An atrophic but otherwise normal breast. The patient had a carcinoma in the contralateral breast.
(arrow) is seen immediately Figure 7. A carcinoma adjacent to an area of glandular elements. There is some haziness of its posterior margin. Its attenuation coefficient was not clearly different from that of the adjacent glandular tissue.
Figure 8. Carcinoma (arrow) lying adjacent to the chest wall. The carcinoma is connected to the chest wall by a band of tissue denser than the surrounding fat. There is fine irregularity of the margin of the carcinoma.
Calcification was less clearly demonstrated with CT than with xeromammography. Vascular calcification that was easily seen on the xeromammogram could not be demonstrated by routine CT techniques. Gross calcification (Figures 10, 11) within a tumor as well as skin thickening (Figure 12) were demonstrated by either method.
Figure 9. Craniocaudal xeromammogram of the deep-seated carcinoma seen in Figure 8. The carcinoma (arrow) was almost missed on this view because it was so close to the chest wall.
Figure 10. Calcification in a large carcinoma. The tumor measures over 6 cm in diameter. Calcification can be seen in its deeper part.
The single fibroadenoma in this series (Figure 13) had a sharp outline. Its attenuation coefficient was not clearly different from that of the adjacent glandular tissue. Extramammary
Areas
In this series, there was not a single case of recognizable abnormality of the internal mammary node chain. In one case, abnormality of the mediastinal nodes was recognized.
Figure 11. Xerogram of the patient in Figure 10 shows the extensive calcification in the carcinoma more clearly than does the CT scan.
CT Scanning
of the Breast
Figure 14. Left axillary lymphadenopathy in carcinoma. The involved lymph nodes are quite grossly enlarged. No corresponding masses can be seen in the contralateral axilla. There is a large carcinoma in the left breast. Figure 12. Skin thickening in an extensive carcinoma. In this supine scan the carcinoma is seen as a large mass merging with the skin. The skin thickening is best seen medial to the mass.
Axillary lymph nodes could be identified on the CT scan. Fat is plentiful in the axilla, and the nodes, both normal and abnormal, stood out against it. Gross lymphadenopathy was readily recognized (Figure 14). Asymmetry of the axillae could be best assessed when the patient lay prone with her arms extended above her head. Radiation Dosage
Radiation dosage was measured in 2 patients by means of four thermoluminescent dosimeters applied to the skin of each breast just below the nipple. The results are presented in Table 2. DISCUSSION
The prone position, with the breasts hanging dependent, separated the tissues of the breast from one another, and provided images that were strikingly similar to the craniocaudal mammogram, so that the image was of a form already familiar to many radiologists. It also ensured that both breasts and both axillae were examined under identical conditions, so that asymmetry was readily perceived. There was some difficulty with the prone position in large patients with large breasts because the aperture of the Table 2. Radiation dosage as measured in 2 patients by means of four thermoluminescent dosimeters placed on the skin of each breast Figure 13. Fibroadenoma (same patient as in Figure 3). The fibroadenoma (f) appears as a sharply defined, rounded mass lesion with a smooth margin. The dense glandular tissue behind it contains lacunae of fat. There is a band of fat, which is free of glandular elements, lying against the chest wall-a normal appearance.
Doust et al. 300
Exposure factors Number of slices Radiation dose alncluded
Patient I
Patient II
120 kV, 480 mAs 22a
120 kV, 205 mAs
3.2 R
1.2 R
three sets of slices
through
the lesion.
10
CT scanner was not always big enough to accommodate the patient and still leave enough space for the breasts to hang free. In Figures 4 and 5 the breasts have come into contact with and have been deformed by the bed of the scanning gantry. The supine images may be more satisfactory for localization of lesions prior to excision, because the patient is in the supine position during surgery. However, the configuration of the breast in the supine patient rendered the breast images difficult to compare with each other and with the mammograms. Large breasts occasionally extended beyond the reconstruction circle when the patient was supine. In the absence of intravenous contrast material, it appears that the attenuation coefficient of uncalcified carcinomas is not significantly different from that of normal ductal and glandular elements (Table 3). This result agrees with the observations of others (3, 5). Fine calcification is not well demonstrated by means of CT. The CT voxels are large when compared with the small flecks of calcium seen in some carcinomas, so that partial volume averaging obscures the calcium. This problem is more serious when thick slices are used. Because calcium may be present in both benign and malignant lesions, it is the pattern of calcification rather than its mere presence that differentiates benign from malignant lesions. Therefore, it is unlikely that digital printouts of the attenuation coefficients of individual pixels, as described for lung lesions (6), will prove useful in the diagnosis of breast carcinoma. However, this technique may be helpful in the axilla, to detect metastatic nodes. It has been shown by others (2, 3, 5) that, when intravenous contrast agent is administered, carcinomas increase their attenuation coefficient in a manner that is sufficiently characteristic to improve the diagnostic accuracy of CT. Intravenous contrast agent was not used in this study, primarily for ethical reasons. The slight added hazard of intravenous contrast agent was thought to be unacceptable until this preliminary investigation indicated that CT mamTable 3.
Attenuation Tissue
Mammary
fat
coefficients
of breast No. of readinas
tissues No. of breasts
17
14
Glandular elements Dense breasts Fatty breasts
33 20 13
25 14 11
Uncalcified
30 6 11
carcinoma
Fibroadenoma Pectoral
muscle
mography might offer some benefit to the patient. The radiation dose was measured at the skin surface of the dependent breasts. The dose for a scout view and a single set of contiguous slices is about 1.2 R. The mid-breast dose is likely to be only slightly less than the surface dose, since the breast was irradiated throughout the 360” rotation of the CT x-ray tube during each exposure and the voltage used (120 kV) was considerably higher than that used in conventional film mammography or xeromammography. If this assumption is correct, the mid-breast dose for CT mammography as performed in this series is likely to be higher than that for xeromammography, suggesting that it is not suitable for use as a mass screening tool (7). The spatial resolution of the images is sufficiently good that some of the criteria of malignancy developed for xerography-e.g., skin thickening, irregularity of the outline of a carcinoma (Figure 7), and stranding running from the mass (8)-can be applied to the CT images. The most striking advantage of the technique seems to be the clarity with which that portion of the breast adjacent to the pectoral musculature is displayed. The band of fat in this area in densely glandular breasts acts as a natural contrast agent. It is probable that the presence of material of higher attenuation coefficient than fat in this zone is a sign of malignancy. A disappointing finding was that there was not a single instance, with the patient either prone or supine, in which the internal mammary lymph nodes were visible. Possibly there was not a case in this series in which the nodes were involved, but this hypothesis appears unlikely in light of the advanced disease demonstrated in some patients. Axillary nodes stood out clearly against the axillary fat. The criteria for abnormal axillary nodes cannot be firmly established on the basis of so small a series. However, asymmetry when compared to the contralateral axilla suggests malignant involvement. An increase in the attenuation coefficient of a node (Hounsfield
units) _____Mean attenuation coefficient -135
Highest value
Lowest value
- 123
-169
Mean SD 10
3 22 - 25
50 50 4
- 56 0 - 56
10 19 12
9
6
33
- 20
12
1
23
32
15
7
11
40
63
_
CT
-7
11
Scanning
of the Breast 301
with intravenous contrast, or the recognition of nodal calcification by means of digital printouts of the attenuation coefficients of individual pixels as described for solitary pulmonary nodules (6), may allow more sensitive detection of metastatic axillary nodal involvement in the future.
3.
4.
5. REFERENCES 6. 1.
Chang CH, Sibala JL, Gallagher
2.
tomography of the breast. ology 124:827-829, 1977 Chang CH, Sibala JL, Fritz SL, et al: Computed tomographic evaluation of the breast. AJR 131:459-464, 1978
JH, et al: Computed A preliminary report. Radi-
CONTINUING (CT SCANNING
1.
2.
3.
4.
MEDICAL
EDUCATION
7.
8.
Chang CH, Sibala JL, Fritz SL, et al: Specific value of computed tomographic breast scanner (CT i M) in diagnosis of breast diseases. Radiology 132:647-652, 1979 Chang CH, Sibala JL, Lin F, et al: Preoperative diagnosis of potentially precancerous breast lesions by computed tomography breast scanner: Preliminary study. Radiology 129:209-210, 1978 Gisvold JJ, Karsell PR, Reese DF, McCullough EC: Clinical evaluation of computerised tomographic mammography. Mayo Clin Proc 52:181-185, 1977 Siegelman SS, Zerhouni EA, Leo FP, et al: CT of the solitary pulmonary nodule. AJR 135:1-13, 1980 Muntz EP, Wilkinson E, George FW: Mammography at reduced doses: Present performance and future possibilities. AJR 134:741-747, 1980 Wolf JN: Xeroradiography of the Breast. Charles C Thomas, Springfield, Ill., 1972
QUESTIONS
OF THE BREAST USING A CONVENTIONAL
CT SCANNER)
CT of the breast can demonstrate intramammary calcification as well as xeromammography. a. True b. False At the back of the breast, immediately against the chest wall there is: a. Particularly dense glandular tissue b. A layer of fatty tissue C. A series of prominent lymph nodes In the absence of intravenous contrast, the CT number of uncalcified breast carcinoma is higher than that of glandular tissue in 90% of cases. a. True b. False The radiation dose from breast CT is: a. Higher than b. Lower than C. The same as conventional film screen mammography.
Doust et al. 302