Download Post-processing subtraction image of T1

Post-processing subtraction image of T1-weighted from T2weighted image: evaluation of theoretical signal intensity
and comparison with STIR image
Poster No.:
C-1925
Congress:
ECR 2015
Type:
Scientific Exhibit
Authors:
M. Nakadate, Y. Machida, Y. Iwasa, Y. Kitazume, U. Tateishi;
Tokyo/JP
Keywords:
Edema, Imaging sequences, Comparative studies, MR, Image
manipulation / Reconstruction, MR physics, Musculoskeletal soft
tissue, Computer applications, Inflammation, Neoplasia
DOI:
10.1594/ecr2015/C-1925
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Page 1 of 8
Aims and objectives
Short TI inversion recovery (STIR) is an established sequence that suppresses short
T1 tissue signals, such as those from fat, and can visualize inflammatory changes,
edematous changes, and tumors with a better contrast [1-3]. However, STIR is not always
performed during routine examinations because it requires additional imaging time.
On the other hand, T1-weighted (T1W) and T2-weighted (T2W) images are obtained
during nearly every examination. With the intention of decreasing the short T1 (fat)
signal and accentuating the long T2 (edematous change) signal, similar to the process
that occurs in creating a STIR image, we focused our attention on the post-processing
subtraction of T1W images from T2W images.
The purpose of this study was to evaluate the feasibility of using T2-T1 subtraction (T2T1sub) images, obtained by the post-processing subtraction of T1W images from T2W
images, as an alternative to STIR images.
Methods and materials
A total of 38 consecutive MRI examinations of the extremities during which T1W, T2W,
and STIR images had been obtained in the same plane were included in this retrospective
study. All the examinations had been performed between January and March 2012.
The MR images were obtained using a 1.5-T MRI system. The T1W, T2W, and STIR
acquisition parameters were as follows: TR/TE, 360-700 msec/10-15 msec; NEX, 1; and
matrix, 256 x 416 (for T1W); TR/TE, 3200-4100/105; NEX, 1; and matrix, 256 x 432 (for
T2W); and TR/TE, 5300-6337/80; inversion time (TI), 130-150 msec; NEX, 1, and matrix,
224 x 304 (for STIR).
For each examination, the T1W image was subtracted from the T2W image on a
workstation to obtain a T2-T1sub image. The high-signal intensities on the T2-T1sub
images were then compared with those on the STIR images as a standard reference.
Continuous lesions were considered to be a single lesion, and the number of abnormal
intensity areas was recorded. All the images were evaluated by a board-certified
radiologist with no knowledge of any clinical information. The MR image evaluation and
clinical diagnosis were also investigated using the medical records (Table1).
Table 1. Patient backgrounds and MR image evaluations
Page 2 of 8
Disease
number
Myositis, Fasciitis
15
Tumor
5
Cystic lesion
3
No abnormal finding
15
In addition, a theoretical spin echo signal intensity contour map of the T2-T1sub image
was created and compared with that of the STIR image. The signal intensity equation and
protocol for drawing the contour maps were based on previously reported methods [1; 4].
The contour maps for each sequence were created using the spin-echo signal intensity
equation for the T1W (TR/TE, 550/10), T2W (TR/TE, 3500/80), and STIR sequence (TR/
TE/TI, 6100/80/150).
Results
Seventy-six abnormal signal intensity areas were found on the STIR images, and 74 of
them were detected on the T2-T1sub images (Table2 and Figures 1-3). Four lesions were
identified as false-positive results. The sensitivity and positive predictive values of the
T2-T1sub images were 97.4% and 94.9%, respectively. A comparison of Figure 4C and
4D showed that the signal intensity distribution in the T2-T1sub image was similar to that
in the STIR image within the physiological T1/T2 range.
Table 2. Abnormal intensity areas detected on STIR images
Disease
Number of abnormal intensity areas
Myositis
33
Fasciitis
4
Subcutaneous edema
19
Tumor
17
Cystic lesion
3
Images for this section:
Page 3 of 8
Fig. 1: A 74-year-old male with myositis. (A) A T2-T1 subtraction image and (B) a STIR
image of the left shoulder and upper extremity show almost the same distribution of high
signal intensity areas. Note that the T2-T1 subtraction image contains respiratory motion
artifacts.
Fig. 2: A 63-year-old male with necrotizing fasciitis of the right thigh. (A) The T2-T1
subtraction image shows an excellent concordance with (B) the STIR image.
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Fig. 3: A 76-year-old male with a pleomorphic sarcoma in the right thigh. (A) The T2T1 subtraction image shows a marked similarity to (B) the STIR image in terms of tumor
characterization, subcutaneous edema, and muscular edematous change.
Page 5 of 8
Fig. 4: Examples of the signal intensity contour maps of (A) T1-weighted, (B) T2weighted, (C) T2-T1 subtraction, and (D) STIR sequences plotted on a T1 (horizontal
axis) and a T2 (vertical axis) plane. The signal intensity contour map of the T2-T1
subtraction shows a strong agreement with that for the STIR. These contour maps
were created using the spin-echo signal intensity equation for the T1-weighted (TR/
TE, 550/10 msec), T2-weighted (TR/TE, 3500/80 msec), and STIR sequence (TR/TE/TI,
6100/80/150 msec).
Page 6 of 8
Conclusion
The subtraction technique is used in daily clinical practice, such as for the subtraction of
pre-contrast from post-contrast enhancement images or out-of-phase from in-phase T1W
images. However, subtraction between different sequences is not common. As far as we
know, only Bonett et al. [5] has previously reported the usefulness of T2-T1sub images
for obtaining evidence of epidural cerebrospinal fluid leakage in cases of spontaneous
intracranial hypotension, but they did not evaluate or discuss the actual creation of such
images. We observed that T2-T1sub images created in this manner are very similar to
STIR images, as shown using clinical images and signal intensity contour maps.
False-positive regions were mostly generated by subtraction artifacts, such as position
gaps between the T1W and T2W images or magnetic field inhomogeneity. These motion
artifacts could be identified as false-positive regions by referring to the original T1W and
T2W images.
In addition, the signal-to-noise ratio were considered to be better for T2-T1sub images
than for STIR images, especially when the subtraction image was generated without a
position gap, but this hypothesis could not be proven in the present study. Furthermore,
because of the use of basic imaging sequences, the same post-processing subtraction
technique can likely be also applied to the head and neck, spine, or pelvic regions.
The relative nature of MRI signal intensity could lead to the following study limitations.
First, when the receiver gain is different between T1W and T2W image, simple subtraction
becomes meaningless and correct weighting is necessary. Second, because these
results were obtained using a small sample size and a single MR machine, confirmation
using a wide variety of MR machines and institutions is needed to generalize the present
findings. In addition, for the widespread using of this subtraction method, the development
of useful software capable of creating subtraction images on the PACS viewer or MR
console system in a simple and user-friendly manner is essential.
In conclusion, the current study has shown that subtraction images obtained by the postprocessing of T1W and T2W images could be a useful alternative to STIR images.
Personal information
Masashi Nakadate, M.D., Ph.D.
Page 7 of 8
Department of Diagnostic Radiology, Medical Hospital, Tokyo Medical and Dental
University, Tokyo, Japan;
[email protected]
Youichi Machida, M.D., Ph.D.
Department of Radiology, Kameda Kyobashi Clinic, Tokyo, Japan.
Yoshihiro Iwasa, M.D.
Department of Diagnostic Radiology, Medical Hospital, Tokyo Medical and Dental
University, Tokyo, Japan.
Yoshio Kitazume, M.D., Ph.D.
Department of Diagnostic Radiology, Medical Hospital, Tokyo Medical and Dental
University, Tokyo, Japan.
Ukihide Tateishi, M.D., Ph.D.
Department of Diagnostic Radiology, Medical Hospital, Tokyo Medical and Dental
University, Tokyo, Japan.
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