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Fast 3D — Imaging — Application and benefits
MagneticResonanceImaging0 Volume 5, Number 6, 1987
542
have also been apparent by MRI. studies of myocardial infarction and cardiomyopathies, wall allows assessment of the direct visualization of the myocardial In addition, infarction. The abnormal wall thickening, a more specific indicator of myocardial end-diastolic (ED) and end-systolic (ES) tomographic images which encompase the entire heart can be directly planimetered to obtain ED and ES volumes from which stroke volumes, biventricular ejection fractions, and regurgitant fractions can be calculated.
FAST 3D - IMAGING - APPLICATIONAND BENEFITS R. Bachus, M. Deimling, and R. Tyrrell Siemens AG UB Med, D 8520 Erlangen,W. Germany Fast 3D gradient echo sequenceslike FLASH (Fast Low Angle Shot, (l)), and FISP (Fast Imaging with Steady Precession (2)) can provide high resolutionisotrpoic3D data sets in a much shorter time compared to 3D spin echo sequences. Fast 3D-Imaging combines all benefits of gradient echo sequences with 3D acquisition: * * * *
high S/N due to gradient echo and low angle volume excitation very thin contiguous slices (thickness less than 1 mm) nearly rectangular slice profile retrospective reconstruction of arbitrary oblique slices from isotropic 3D-data
All these advantages of the 3D technique are not new but with the invention of fast imaging, they can be realized in routine clinical work. A major point for clinical applications gradient echo sequences.
is the flip angle dependent contrast behaviour seen with fast
.
Fig. 1: FLASH-Signal intensity as function of Tl and excitation angle
.m
., lo
l.&+,~
Fig. 2: FISP Signal intensity as a function of T~/T~ and excitation angle
Fig. 1 shows the signal for the FLASH-sequence as a function of flip angle and the relaxation time Tl. FCJr figh signal intensity can be observed for most tissues low flip angles there is almost no Tl-dispersion. using a flip angle less than 90 deg. In contrast, a different signal behaviour is seen with the FISP sequence. Signal amplitude basically depends on the ratio of the relaxation times TI/T2. The plot of fig. 2 shows the highest signal intensity for a flip angle of 90 deg and a ratio Tl/T2=1 (which holds true for liquids or liquid like tissues).
Fig.3: Comparison between 3D FLASH (upper image) and 3D
FISP (lower image)
3D imaFig.&: ,ging of theknee measured sagittal images on the left reconstructions along the crucial ligaments on the right.
Abstractsl Chairman: MARK
543
HAACKE
Neuroradiological application of 3D imaging to a patient with breast metastasis elludes the potential complementary roles of FISP and FLASH in evaluating intracranial processes. Representative images of the 128 image data sets are shown in the two images in fig. 3 with FLASH (upper image) and FISP (lower image) respectively. Both data sets utilize a 256 x 256 matrix with 1.7mm slice thickness. The FLASH image shows good anatomic detail with grey/white contrast while FISP highlights the fluid of both the CSF and edema, the latter serving to better delinate the tumor boundary. An example of Musculoskeletal 3D-images with isotropic resolution 0.8 mm is given in fig. 4. Using an excitation angle of 30 deg., tissue differentiation is maintained between trabecular bone, cortical bone, cartilage, fat, menisci, tendon and muscle. The 3D-method enables one to reconstruct images in any desired Oblique reconstructions along the crucial ligaments are shown in fig. 4 from an original meaorientation. sured sag&ttal data set. Conclusion Although clinical experience with 3D-volume imaging using fast sequences like FLASH and FISP is limited, the anatomic detail provided in very thin slices shows much potential. In particular the subsequent reconstruction of arbitrary oblique views is a major advantage for orthopaedic applications. References (1) A. Haase, J. Frahm, D. Matthaei, K.D. Merboldt and W. Haenike, 4th SMRM London. Book of Abstr.: 980(1985) (2) A. Oppelt, R. Graumann, H. Barfuss, H. Fischer, W. Hart1 and W. Schajor, Electromedica 54, 15 (1986)
THE IMPACT OF STEADY STATE IMAGING ON GD-DTPA-ENHANCED
MAGNETIC RESONANCE IMAGING
Michael Laniado, Bernhard Sander, Wolfgang Schorner, Wolfgang Kornmesser, Klinikum Charlottenburg,
Freie Universitat,
Michael Deimling, Roland Felix
Berlin
Our efforts at Klinikum Charlottenburg of Freie Universitat Berlin over the last 18 months have been directed mainly towards the clinical application of fast imaging sequences to gadolinium-DTPA (Gd-DTPA) enhanced MRI. Steady state sequences were implemented on a comercial 0.5 T Siemens Magnetom (gradient strength Gd-DTPA/dimeglumine was made available by Schering AG, Berlin. 3 mT/m). As part one of our clinical studies with steady state sequences and Gd-DTPA 73 patients with intracranial tumors were investigated in order to determine the most appropriate excitation pulse angle for visualization of contrast enhancement. FLASH sequences (Fast Low Angle Shot) (1) with a TR of 40 msec and a TE of 16 msec were used for single slice scans. In each patient excitation pulse angles of 10, 40, 60 and 90 degree were employed and results were compared. 40 degree turned out to be the most advantageous excitation pulse angle for Gd-DTPA-enhanced FLASH imaging of intracranial tumors (2). In 57 patients with intracranial tumors the 40 degree FLASH sequence (TR 40 msec, TE 16 msec) was used to perform dynamic MRI studies (3). Prior to and following bolus injection of Gd-DTPA (0.1 mmollkg equivalent to 0.2 ml/kg, injection time was 6 to 12 set) single slice FLASH images were acquired on 128 x 128 matrix Due to scan times of 5 seconds and interscan delays of 5 to 6 seconds the with single signal acquisition. time resolution of contrast enhancement was about 10 seconds. Tumor enhancement was measured by a region of interest technique and values were normalized to the precontrast scan. Certain tumor types showed characteristic time-signal intensity (time-SI) curves. In 10 of 14 meningiomas immediate up-slopes of the time-S1 curve were measured followed by a gradual decrease. In 7 acoustic neurOmas the up-slope of the time-S1 curve was less steep and peak values were measured 4-5 minutes after injection. In 11 glianas slowly increasing time-S1 curves were observed. We conclude that dynamic MRI can potentially be used to narrow differential diagnosis in intracranial tumors. Basically the same procedure was applied in 21 patients with renal tumors (4). Twelve tumors displayed steep increases of SI immediately after Gd-DTPA injection. Nine lesions either showed lack of enhancement or In renal parenchyma corticcrmedullary differentiation small increases of SI after administration of contrast. In 13 cases angiowas highlighted in the arterial phase of bolus distribution and was fading thereafter. Tumors with immediate enhancement in dynamic MRI were angiography confirmed as hypergraphy was performed. Based on our knowledge from dynamic CT (5) we conclude that dynamic MRI vascularised lesions and vice versa. provides data on tumor vascularity and renal function. Image artifacts regarded as limiting a single breath-hold Furthermore, Gd-DTPA
due to various biological motions and the lack of a suitable bowel contrast agent are factors in abdominalMR1 (6). With fast imaging sequences images can be obtained within which in turn significantly reduces artifacts due to respiration and peristalsis. now is available for GI-tract enhancement.
Orally administered Gd-DTPA (1.0 mmol/l, 10 ml/kg) was used along with FLASH sequences (TR 40 ms, TE 16 ms, flip angle 40 degree) in 20 healthy male volunteers (7). High signal flow artifacts (abdominal aorta, inferior vena cava) due to phase encoding errors reduced image quality of Gd-DTPA enhanced FLASH images of the upper abdomen. Therefore, the pancreatic head could not be delineated although Gd-DTPA highlighted the C-loop of the duodenum. However, in the lower abdomen no image degradation by flow artifacts was observed and the enhanced GI-tract could clearly be differentiated frcm adjacent structures. Freezing of peristalsis provided visualization of individual bowel loops on FLASH images.
542
have also been apparent by MRI. studies of myocardial infarction and cardiomyopathies, wall allows assessment of the direct visualization of the myocardial In addition, infarction. The abnormal wall thickening, a more specific indicator of myocardial end-diastolic (ED) and end-systolic (ES) tomographic images which encompase the entire heart can be directly planimetered to obtain ED and ES volumes from which stroke volumes, biventricular ejection fractions, and regurgitant fractions can be calculated.
FAST 3D - IMAGING - APPLICATIONAND BENEFITS R. Bachus, M. Deimling, and R. Tyrrell Siemens AG UB Med, D 8520 Erlangen,W. Germany Fast 3D gradient echo sequenceslike FLASH (Fast Low Angle Shot, (l)), and FISP (Fast Imaging with Steady Precession (2)) can provide high resolutionisotrpoic3D data sets in a much shorter time compared to 3D spin echo sequences. Fast 3D-Imaging combines all benefits of gradient echo sequences with 3D acquisition: * * * *
high S/N due to gradient echo and low angle volume excitation very thin contiguous slices (thickness less than 1 mm) nearly rectangular slice profile retrospective reconstruction of arbitrary oblique slices from isotropic 3D-data
All these advantages of the 3D technique are not new but with the invention of fast imaging, they can be realized in routine clinical work. A major point for clinical applications gradient echo sequences.
is the flip angle dependent contrast behaviour seen with fast
.
Fig. 1: FLASH-Signal intensity as function of Tl and excitation angle
.m
., lo
l.&+,~
Fig. 2: FISP Signal intensity as a function of T~/T~ and excitation angle
Fig. 1 shows the signal for the FLASH-sequence as a function of flip angle and the relaxation time Tl. FCJr figh signal intensity can be observed for most tissues low flip angles there is almost no Tl-dispersion. using a flip angle less than 90 deg. In contrast, a different signal behaviour is seen with the FISP sequence. Signal amplitude basically depends on the ratio of the relaxation times TI/T2. The plot of fig. 2 shows the highest signal intensity for a flip angle of 90 deg and a ratio Tl/T2=1 (which holds true for liquids or liquid like tissues).
Fig.3: Comparison between 3D FLASH (upper image) and 3D
FISP (lower image)
3D imaFig.&: ,ging of theknee measured sagittal images on the left reconstructions along the crucial ligaments on the right.
Abstractsl Chairman: MARK
543
HAACKE
Neuroradiological application of 3D imaging to a patient with breast metastasis elludes the potential complementary roles of FISP and FLASH in evaluating intracranial processes. Representative images of the 128 image data sets are shown in the two images in fig. 3 with FLASH (upper image) and FISP (lower image) respectively. Both data sets utilize a 256 x 256 matrix with 1.7mm slice thickness. The FLASH image shows good anatomic detail with grey/white contrast while FISP highlights the fluid of both the CSF and edema, the latter serving to better delinate the tumor boundary. An example of Musculoskeletal 3D-images with isotropic resolution 0.8 mm is given in fig. 4. Using an excitation angle of 30 deg., tissue differentiation is maintained between trabecular bone, cortical bone, cartilage, fat, menisci, tendon and muscle. The 3D-method enables one to reconstruct images in any desired Oblique reconstructions along the crucial ligaments are shown in fig. 4 from an original meaorientation. sured sag&ttal data set. Conclusion Although clinical experience with 3D-volume imaging using fast sequences like FLASH and FISP is limited, the anatomic detail provided in very thin slices shows much potential. In particular the subsequent reconstruction of arbitrary oblique views is a major advantage for orthopaedic applications. References (1) A. Haase, J. Frahm, D. Matthaei, K.D. Merboldt and W. Haenike, 4th SMRM London. Book of Abstr.: 980(1985) (2) A. Oppelt, R. Graumann, H. Barfuss, H. Fischer, W. Hart1 and W. Schajor, Electromedica 54, 15 (1986)
THE IMPACT OF STEADY STATE IMAGING ON GD-DTPA-ENHANCED
MAGNETIC RESONANCE IMAGING
Michael Laniado, Bernhard Sander, Wolfgang Schorner, Wolfgang Kornmesser, Klinikum Charlottenburg,
Freie Universitat,
Michael Deimling, Roland Felix
Berlin
Our efforts at Klinikum Charlottenburg of Freie Universitat Berlin over the last 18 months have been directed mainly towards the clinical application of fast imaging sequences to gadolinium-DTPA (Gd-DTPA) enhanced MRI. Steady state sequences were implemented on a comercial 0.5 T Siemens Magnetom (gradient strength Gd-DTPA/dimeglumine was made available by Schering AG, Berlin. 3 mT/m). As part one of our clinical studies with steady state sequences and Gd-DTPA 73 patients with intracranial tumors were investigated in order to determine the most appropriate excitation pulse angle for visualization of contrast enhancement. FLASH sequences (Fast Low Angle Shot) (1) with a TR of 40 msec and a TE of 16 msec were used for single slice scans. In each patient excitation pulse angles of 10, 40, 60 and 90 degree were employed and results were compared. 40 degree turned out to be the most advantageous excitation pulse angle for Gd-DTPA-enhanced FLASH imaging of intracranial tumors (2). In 57 patients with intracranial tumors the 40 degree FLASH sequence (TR 40 msec, TE 16 msec) was used to perform dynamic MRI studies (3). Prior to and following bolus injection of Gd-DTPA (0.1 mmollkg equivalent to 0.2 ml/kg, injection time was 6 to 12 set) single slice FLASH images were acquired on 128 x 128 matrix Due to scan times of 5 seconds and interscan delays of 5 to 6 seconds the with single signal acquisition. time resolution of contrast enhancement was about 10 seconds. Tumor enhancement was measured by a region of interest technique and values were normalized to the precontrast scan. Certain tumor types showed characteristic time-signal intensity (time-SI) curves. In 10 of 14 meningiomas immediate up-slopes of the time-S1 curve were measured followed by a gradual decrease. In 7 acoustic neurOmas the up-slope of the time-S1 curve was less steep and peak values were measured 4-5 minutes after injection. In 11 glianas slowly increasing time-S1 curves were observed. We conclude that dynamic MRI can potentially be used to narrow differential diagnosis in intracranial tumors. Basically the same procedure was applied in 21 patients with renal tumors (4). Twelve tumors displayed steep increases of SI immediately after Gd-DTPA injection. Nine lesions either showed lack of enhancement or In renal parenchyma corticcrmedullary differentiation small increases of SI after administration of contrast. In 13 cases angiowas highlighted in the arterial phase of bolus distribution and was fading thereafter. Tumors with immediate enhancement in dynamic MRI were angiography confirmed as hypergraphy was performed. Based on our knowledge from dynamic CT (5) we conclude that dynamic MRI vascularised lesions and vice versa. provides data on tumor vascularity and renal function. Image artifacts regarded as limiting a single breath-hold Furthermore, Gd-DTPA
due to various biological motions and the lack of a suitable bowel contrast agent are factors in abdominalMR1 (6). With fast imaging sequences images can be obtained within which in turn significantly reduces artifacts due to respiration and peristalsis. now is available for GI-tract enhancement.
Orally administered Gd-DTPA (1.0 mmol/l, 10 ml/kg) was used along with FLASH sequences (TR 40 ms, TE 16 ms, flip angle 40 degree) in 20 healthy male volunteers (7). High signal flow artifacts (abdominal aorta, inferior vena cava) due to phase encoding errors reduced image quality of Gd-DTPA enhanced FLASH images of the upper abdomen. Therefore, the pancreatic head could not be delineated although Gd-DTPA highlighted the C-loop of the duodenum. However, in the lower abdomen no image degradation by flow artifacts was observed and the enhanced GI-tract could clearly be differentiated frcm adjacent structures. Freezing of peristalsis provided visualization of individual bowel loops on FLASH images.