- Email: [email protected]
Fast magnetic resonance in vascular diseases of the abdomen
Magnetic Resonance Printed in the USA.
Imaging, Vol. 6, pp. 473-477, All rights reserved.
1988 Copyright
0730-725X/88 $3.00 + .I0 0 1988 Pergamon Pressplc
l Case Report
FAST MAGNETIC
RESONANCE
IN VASCULAR
DISEASES
OF THE ABDOMEN
BHARAT RAVAL, MADAN KULKARNI, PONNADA NARAYANA, AND SNEHAL MEHTA Department of Radiology, The University of Texas Medical School at Houston, 6431 Fannin, Room 2.134, Houston, Texas 77030 Fast magnetic resonance (MR) imaging provides a consistent and predictable appearance of vascular abnormalities as shown by four patients with thrombi, dissection and aneurysm. Fast MR images are obtained during breatbholding, resulting in an absence of respiratory motion artifacts. The time of MR study is much less with fast MR than with spin echo sequences. Keywords:
Blood vessels; Diseases-vascular
system-magnetic
Electric Signa (Milwaukee, WI) system. Initially, spin echo images were obtained at TR800, TE20 and TR2000 TE20-80. Then fast images were obtained using gradient recalled acquisition in steady state (GRASS) sequences. Axial images were obtained with TR 21 ms, TE 12 ms, and a flip angle of 30”. The acquisition time was 11 seconds for each image. Images were obtained sequentially one slice at a time while the patient was holding breath for each data acquisition. The spin echo axial image at the level of hepatic veins shows tumor in the vena cava (Fig. 1A). The vascular invasion by the tumor was seen better on GRASS sequence (Fig. 1B). A pathological diagnosis of spindle cell sarcoma was made on bronchoscopy of the left lung lesion.
Recent developments in magnetic resonance (MR) allow acquisition of images typically in a few seconds. These methods use small flip angles which reduce the time needed for magnetization to recover from saturation. Fast imaging techniques are attractive because they have the potential to reduce respiratory motion artifacts and shorten the time for acquiring an MR study.3s4*7*9However, the contrast in these images is quite different from that observed in spin echo sequences which are widely employed currently. In this report, we present four patients with vascular disease studied using Gradient Recalled Acquisition in the Steady State (GRASS). CASE
resonance imaging.
REPORTS
Case I A thirty-three year old male with a history of alcoholic liver cirrhosis diagnosed 18 months prior, presented with two months’ history of hemoptysis and shortness of breath. His liver function tests were abnormal. Chest X-ray demonstrated a left hilar mass with left upper lobe collapse. Computed tomography (CT) of the abdomen showed tumor involving the liver and extending into the intrahepatic portion of vena cava. MR imaging was performed using a 1.5 T General
Case 2 A fifty-six year old female was diagnosed of having systemic lupus erythematosis, confirmed by renal biopsy in 1985. She was hypertensive at that time. A year later, she presented with abdominal pain. Angiography showed a type III dissection involving the abdominal aorta. She was managed conservatively with antihypertensive medication. MR images one year later demonstrated the aorta, but evaluation of the lumen was suboptimal using spin echo technique
Address correspondence to Bharat Raval, M.D., Depart-
RECEIVED 12/22/87; ACCEPTED l/l l/88. AcknowledgmentWe are grateful to Carol Hitchcock for preparation of the manuscript and Jay Johnson for the illustrations.
ment of Radiology, the University of Texas Medical School at Houston, 6431 Fannin, Room 2.134, Houston, TX 77030. 473
414
Magnetic Resonance Imaging 0 Volume 6, Number 4, 1988
-
(A)
(B)
Fig. 1. Case 1: Tumor thrombus in inferior vena cava. (A) Axial spin echo image TR800 TE20 shows tumor involving the liver and inferior vena cava as an area of increased signal. (B) GRASS sequence at the same level demonstrates the narrow residual lumen of inferior vena cava as bright signal (arrows) separate from tumor thrombus. Also note collateral veins in the anterior abdominal wall and around hemiazygous vein are well visualized.
(A)
(B)
Fig. 2. Case 2: Aortic dissection. (A) Respiratory phase encoding artifacts limit assessment of the aorta on the spin echo image obtained at TRSOO TE20. (B) GRASS image at the same level shows the intimal flap (arrow). No artifact from respiration is present because short scanning time permits data acquisition during breath holding.
because of phase encoding artifacts due to respiratory motion (Fig. 2A). The GRASS sequence showed the intimal flap very well (Fig. 2B). A real time abdominal ultrasound examination confirmed the presence of an intimal flap in the aorta.
Case 3 A thirty-three year old male had splenectomy after trauma. Postoperatively, the patient developed pulmonary embolism as proven by an abnormal perfusion lung scan and pulmonary angiography. An
MRI in vascular
diseases 0 BHARAT RAVAL ET AL
abdominal CT performed to assess for postoperative complications revealed portal vein thrombosis as an incidental finding. He was treated with anticoagulants. Subsequently, he developed further episodes of pulmonary embolism while on anticoagulants. MR study was performed to evaluate venous systems in the abdomen, pelvis and legs. Axial spin echo images were suboptimal due to motion artifact. GRASS images in the axial plane demonstrated a thrombus and narrowing of the lumen of the inferior vena cava (Fig. 3A). Subsequently, cardiac gated coronal spin echo slices through the inferior vena cava were obtained to confirm clot (Fig. 3B). An extensive workup did not reveal any predisposition to vasculitis or hypercoagulable state except the post splenectomy status.
475
rysm (Fig. 4B) because of high signal from the blood in the lumen. No evidence of hemorrhage was seen on spin echo or GRASS sequences. Because of the patient’s age and size of the aneurysm, surgery was not undertaken. He has been followed since by ultrasound and MR without any change in the aneurysm. DISCUSSION
An eighty-four year old man with abdominal pain who was known to have an abdominal aortic aneurysm was referred for abdominal MR to assess for leakage from the aneurysm. Axial spin echo images showed the aneurysm with slow flow (Fig. 4A). The GRASS image revealed the aneurysm as well but provided a more precise assessment of lumen of the aneu-
Theoretically, high contrast differences exist between flowing blood and surrounding tissues in magnetic resonance. In practice, when utilizing spin echo sequences, the signal from flowing blood can be dark or bright depending upon speed and direction of blood flow and position of the slice in a multislice volume. The dark appearance (“flow void”) is produced by high velocity, turbulence and dephasing.’ Increased signal of flowing blood may occur due to diastolic pseudogating, flow related enhancement and with even echo rephasing.’ Thus demonstration of vascular diseases by spin echo MR is complex and variable.‘** Various strategies have been applied to overcome these problems. 2*6In fast MR images, flowing blood always has a bright signal. GRASS images are ob-
(A)
09
Case 4
Fig. 3. Case 3: Inferior vena cava thrombus. Axial spin echo images (not shown) were limited by motion artifacts. (A) Axial GRASS images reveal thrombus (arrow) in the lower part of inferior vena cava and the normal lumen at the level of kidneys. (B) Coronal cardiac gated spin echo image confirms partially occluding thrombus in the inferior vena cava.
476
Magnetic Resonance Imaging 0 Volume 6, Number 4, 1988
(4
@I
Fig. 4. Aortic aneurysm. (A) Spin echo image TR800 TE200 shows the aneurysm quite well. (B) GRASS the aneurysm as well, but the interphase between lumen and thrombus appears better defined.
one slice at a time using a short acquisition time, therefore, only relaxed spins wash into the imaging plane. Furthermore, GRASS sequence does not use a 180” refocusing radiofrequency pulse so the spins in flowing blood excited by the selective radiofrequency pulse always produce an MR signal irrespective of their position.7,9 In these four cases, tumor, intimal flap, thrombus and aneurysm were easily recognized on fast MR images. The bright signal from the blood vessel simulates dynamic contrast enhanced computed tomography or angiography. We found universal acceptance of fast MR sequences among the referring physicians. Acquisition of such information without the use of contrast or catheter makes fast MR truly noninvasive. GRASS images, unlike spin echo images, are acquired during breath holding because of the short acquisition time. This eliminates the phase encoding artifact from respiratory motion which was problematic in cases two and three on the spin echo sequence. Furthermore, GRASS images are acquired in much less time than spin echo examinations resulting in a shorter examination time per patient. In spin echo images, magnetic susceptibility artifacts are eliminated by a refocusing 180” radiofrequency pulse. GRASS does not use such a pulse so magnetic susceptibility artifacts are present. However, we did not find them interfering with assessment of blood vessels. This study suggests that the fast MR sequence is tained
sequence
reveals
superior to conventional spin echo imaging in the demonstration of vascular diseases. Recently, GRASS MR has been suggested as a supplement to spin echo sequences to assess vascular patency in tumors and vessel obstruction or aneurysm.5 We recommend that if MR is being considered for assessment of any vascular abnormality, fast MR imaging with small flip angle should be used rather than a spin echo sequence. This will result in a predictable and reliable assessment of vascular disease in a shorter time. As further experience accumulates, fast MR scanning may replace dynamic CT with bolus enhancement or angiography in the assessment of vascular diseases in selected patients. REFERENCES 1. Bradley, W.G. Magnetic resonance appearance of flowing blood and cerebrospinal fluid. M.N. Brant-Zawadzki, D. Norman, eds. Magnetic Resonance Imaging of the central nervous system, New York, Raven Press, 83-96; 1987. 2. Dinsmore, R.E.; Weeden, V.; Rosen, B.; Wismer, G.L.; Miller, S.W.; Brady, T.J. Phase-offset technique to distinguish slow blood flow and thrombus on MR images. AJR 148:634-636; 1987. 3. Frahm, J.; Haase, A.; Matthaei, D. Rapid three-dimensional MR imaging using the FLASH technique. J. Com-
put. Assist. Tomogr. 10:363-368; 1986. 4. Haase, A.; Frahm, J.; Matthaei, D.; Hanicke, W.; Merboldt, K.D. FLASH imaging. Rapid NMR imaging using low flip angle pulses. J. Magn. Reson. 67:258-266; 1986. 5. Haggar, A.M.; Froelich, J.W. Vascular patency deter-
MRI in vascular diseases 0 BHARATRAVALET AL
mined by Gradient Recalled Acquisition in the Steady State. Book of Abstracts, Fifth Annual Meeting of the Society for Magnetic Resonance Imaging, San Antonio, Texas, 1987. 6. Rapoport, S.; Sostman, H.D.; Pope, C.; Camputaro, C.M.; Holcomb, W.; Gore, J.C. Venous clots: Evaluation with MR imaging. Radiology 162:527-530; 1987. 7. Utz, J-A.; Herfkens, R-J.; Johnson, CD., et al. Two-
417
second MR images: Comparison with spin-echo images in 29 patients. AJR 148:629-633; 1987. 8. Valk, P.E.; Hale, J.D.; Crooks, L.E.; et al. MRI blood flow: Correlation of image appearance with spin echo phase shift and signal intensity. AJR 146:931-939; 1986. 9. Wehrli, F.W. Introduction to fast scan magnetic resonance. General Electric Medical Systems, Milwaukee, 1987.
Imaging, Vol. 6, pp. 473-477, All rights reserved.
1988 Copyright
0730-725X/88 $3.00 + .I0 0 1988 Pergamon Pressplc
l Case Report
FAST MAGNETIC
RESONANCE
IN VASCULAR
DISEASES
OF THE ABDOMEN
BHARAT RAVAL, MADAN KULKARNI, PONNADA NARAYANA, AND SNEHAL MEHTA Department of Radiology, The University of Texas Medical School at Houston, 6431 Fannin, Room 2.134, Houston, Texas 77030 Fast magnetic resonance (MR) imaging provides a consistent and predictable appearance of vascular abnormalities as shown by four patients with thrombi, dissection and aneurysm. Fast MR images are obtained during breatbholding, resulting in an absence of respiratory motion artifacts. The time of MR study is much less with fast MR than with spin echo sequences. Keywords:
Blood vessels; Diseases-vascular
system-magnetic
Electric Signa (Milwaukee, WI) system. Initially, spin echo images were obtained at TR800, TE20 and TR2000 TE20-80. Then fast images were obtained using gradient recalled acquisition in steady state (GRASS) sequences. Axial images were obtained with TR 21 ms, TE 12 ms, and a flip angle of 30”. The acquisition time was 11 seconds for each image. Images were obtained sequentially one slice at a time while the patient was holding breath for each data acquisition. The spin echo axial image at the level of hepatic veins shows tumor in the vena cava (Fig. 1A). The vascular invasion by the tumor was seen better on GRASS sequence (Fig. 1B). A pathological diagnosis of spindle cell sarcoma was made on bronchoscopy of the left lung lesion.
Recent developments in magnetic resonance (MR) allow acquisition of images typically in a few seconds. These methods use small flip angles which reduce the time needed for magnetization to recover from saturation. Fast imaging techniques are attractive because they have the potential to reduce respiratory motion artifacts and shorten the time for acquiring an MR study.3s4*7*9However, the contrast in these images is quite different from that observed in spin echo sequences which are widely employed currently. In this report, we present four patients with vascular disease studied using Gradient Recalled Acquisition in the Steady State (GRASS). CASE
resonance imaging.
REPORTS
Case I A thirty-three year old male with a history of alcoholic liver cirrhosis diagnosed 18 months prior, presented with two months’ history of hemoptysis and shortness of breath. His liver function tests were abnormal. Chest X-ray demonstrated a left hilar mass with left upper lobe collapse. Computed tomography (CT) of the abdomen showed tumor involving the liver and extending into the intrahepatic portion of vena cava. MR imaging was performed using a 1.5 T General
Case 2 A fifty-six year old female was diagnosed of having systemic lupus erythematosis, confirmed by renal biopsy in 1985. She was hypertensive at that time. A year later, she presented with abdominal pain. Angiography showed a type III dissection involving the abdominal aorta. She was managed conservatively with antihypertensive medication. MR images one year later demonstrated the aorta, but evaluation of the lumen was suboptimal using spin echo technique
Address correspondence to Bharat Raval, M.D., Depart-
RECEIVED 12/22/87; ACCEPTED l/l l/88. AcknowledgmentWe are grateful to Carol Hitchcock for preparation of the manuscript and Jay Johnson for the illustrations.
ment of Radiology, the University of Texas Medical School at Houston, 6431 Fannin, Room 2.134, Houston, TX 77030. 473
414
Magnetic Resonance Imaging 0 Volume 6, Number 4, 1988
-
(A)
(B)
Fig. 1. Case 1: Tumor thrombus in inferior vena cava. (A) Axial spin echo image TR800 TE20 shows tumor involving the liver and inferior vena cava as an area of increased signal. (B) GRASS sequence at the same level demonstrates the narrow residual lumen of inferior vena cava as bright signal (arrows) separate from tumor thrombus. Also note collateral veins in the anterior abdominal wall and around hemiazygous vein are well visualized.
(A)
(B)
Fig. 2. Case 2: Aortic dissection. (A) Respiratory phase encoding artifacts limit assessment of the aorta on the spin echo image obtained at TRSOO TE20. (B) GRASS image at the same level shows the intimal flap (arrow). No artifact from respiration is present because short scanning time permits data acquisition during breath holding.
because of phase encoding artifacts due to respiratory motion (Fig. 2A). The GRASS sequence showed the intimal flap very well (Fig. 2B). A real time abdominal ultrasound examination confirmed the presence of an intimal flap in the aorta.
Case 3 A thirty-three year old male had splenectomy after trauma. Postoperatively, the patient developed pulmonary embolism as proven by an abnormal perfusion lung scan and pulmonary angiography. An
MRI in vascular
diseases 0 BHARAT RAVAL ET AL
abdominal CT performed to assess for postoperative complications revealed portal vein thrombosis as an incidental finding. He was treated with anticoagulants. Subsequently, he developed further episodes of pulmonary embolism while on anticoagulants. MR study was performed to evaluate venous systems in the abdomen, pelvis and legs. Axial spin echo images were suboptimal due to motion artifact. GRASS images in the axial plane demonstrated a thrombus and narrowing of the lumen of the inferior vena cava (Fig. 3A). Subsequently, cardiac gated coronal spin echo slices through the inferior vena cava were obtained to confirm clot (Fig. 3B). An extensive workup did not reveal any predisposition to vasculitis or hypercoagulable state except the post splenectomy status.
475
rysm (Fig. 4B) because of high signal from the blood in the lumen. No evidence of hemorrhage was seen on spin echo or GRASS sequences. Because of the patient’s age and size of the aneurysm, surgery was not undertaken. He has been followed since by ultrasound and MR without any change in the aneurysm. DISCUSSION
An eighty-four year old man with abdominal pain who was known to have an abdominal aortic aneurysm was referred for abdominal MR to assess for leakage from the aneurysm. Axial spin echo images showed the aneurysm with slow flow (Fig. 4A). The GRASS image revealed the aneurysm as well but provided a more precise assessment of lumen of the aneu-
Theoretically, high contrast differences exist between flowing blood and surrounding tissues in magnetic resonance. In practice, when utilizing spin echo sequences, the signal from flowing blood can be dark or bright depending upon speed and direction of blood flow and position of the slice in a multislice volume. The dark appearance (“flow void”) is produced by high velocity, turbulence and dephasing.’ Increased signal of flowing blood may occur due to diastolic pseudogating, flow related enhancement and with even echo rephasing.’ Thus demonstration of vascular diseases by spin echo MR is complex and variable.‘** Various strategies have been applied to overcome these problems. 2*6In fast MR images, flowing blood always has a bright signal. GRASS images are ob-
(A)
09
Case 4
Fig. 3. Case 3: Inferior vena cava thrombus. Axial spin echo images (not shown) were limited by motion artifacts. (A) Axial GRASS images reveal thrombus (arrow) in the lower part of inferior vena cava and the normal lumen at the level of kidneys. (B) Coronal cardiac gated spin echo image confirms partially occluding thrombus in the inferior vena cava.
476
Magnetic Resonance Imaging 0 Volume 6, Number 4, 1988
(4
@I
Fig. 4. Aortic aneurysm. (A) Spin echo image TR800 TE200 shows the aneurysm quite well. (B) GRASS the aneurysm as well, but the interphase between lumen and thrombus appears better defined.
one slice at a time using a short acquisition time, therefore, only relaxed spins wash into the imaging plane. Furthermore, GRASS sequence does not use a 180” refocusing radiofrequency pulse so the spins in flowing blood excited by the selective radiofrequency pulse always produce an MR signal irrespective of their position.7,9 In these four cases, tumor, intimal flap, thrombus and aneurysm were easily recognized on fast MR images. The bright signal from the blood vessel simulates dynamic contrast enhanced computed tomography or angiography. We found universal acceptance of fast MR sequences among the referring physicians. Acquisition of such information without the use of contrast or catheter makes fast MR truly noninvasive. GRASS images, unlike spin echo images, are acquired during breath holding because of the short acquisition time. This eliminates the phase encoding artifact from respiratory motion which was problematic in cases two and three on the spin echo sequence. Furthermore, GRASS images are acquired in much less time than spin echo examinations resulting in a shorter examination time per patient. In spin echo images, magnetic susceptibility artifacts are eliminated by a refocusing 180” radiofrequency pulse. GRASS does not use such a pulse so magnetic susceptibility artifacts are present. However, we did not find them interfering with assessment of blood vessels. This study suggests that the fast MR sequence is tained
sequence
reveals
superior to conventional spin echo imaging in the demonstration of vascular diseases. Recently, GRASS MR has been suggested as a supplement to spin echo sequences to assess vascular patency in tumors and vessel obstruction or aneurysm.5 We recommend that if MR is being considered for assessment of any vascular abnormality, fast MR imaging with small flip angle should be used rather than a spin echo sequence. This will result in a predictable and reliable assessment of vascular disease in a shorter time. As further experience accumulates, fast MR scanning may replace dynamic CT with bolus enhancement or angiography in the assessment of vascular diseases in selected patients. REFERENCES 1. Bradley, W.G. Magnetic resonance appearance of flowing blood and cerebrospinal fluid. M.N. Brant-Zawadzki, D. Norman, eds. Magnetic Resonance Imaging of the central nervous system, New York, Raven Press, 83-96; 1987. 2. Dinsmore, R.E.; Weeden, V.; Rosen, B.; Wismer, G.L.; Miller, S.W.; Brady, T.J. Phase-offset technique to distinguish slow blood flow and thrombus on MR images. AJR 148:634-636; 1987. 3. Frahm, J.; Haase, A.; Matthaei, D. Rapid three-dimensional MR imaging using the FLASH technique. J. Com-
put. Assist. Tomogr. 10:363-368; 1986. 4. Haase, A.; Frahm, J.; Matthaei, D.; Hanicke, W.; Merboldt, K.D. FLASH imaging. Rapid NMR imaging using low flip angle pulses. J. Magn. Reson. 67:258-266; 1986. 5. Haggar, A.M.; Froelich, J.W. Vascular patency deter-
MRI in vascular diseases 0 BHARATRAVALET AL
mined by Gradient Recalled Acquisition in the Steady State. Book of Abstracts, Fifth Annual Meeting of the Society for Magnetic Resonance Imaging, San Antonio, Texas, 1987. 6. Rapoport, S.; Sostman, H.D.; Pope, C.; Camputaro, C.M.; Holcomb, W.; Gore, J.C. Venous clots: Evaluation with MR imaging. Radiology 162:527-530; 1987. 7. Utz, J-A.; Herfkens, R-J.; Johnson, CD., et al. Two-
417
second MR images: Comparison with spin-echo images in 29 patients. AJR 148:629-633; 1987. 8. Valk, P.E.; Hale, J.D.; Crooks, L.E.; et al. MRI blood flow: Correlation of image appearance with spin echo phase shift and signal intensity. AJR 146:931-939; 1986. 9. Wehrli, F.W. Introduction to fast scan magnetic resonance. General Electric Medical Systems, Milwaukee, 1987.