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Tokai University develops DWI for total body imaging

Best Practice
Takahara, Taro, M.D., Ph.D. Kanagawa, Tokai University
Van Cauteren, Marc, Ph.D. Philips Healthcare

Taro Takahara, M.D. is assistant professor of radiology at Tokai University Hospital (1200 beds) in Isehara City, Kanagawa Prefecture, Japan. A privately funded institution,Tokai University purchased its first MRI scanner more than 15 years ago. Since then four Philips scanners were installed.Two of them are Intera 1.5T systems with Nova gradients, currently operating at Release 10. The DWIBS exams described in this article are performed on these two systems. DWIBS is an acronym for Diffusion weighted Whole body Imaging with Background body signal Suppression.

Taro Takahara, M.D. DWIBS neck shoulder The EPI-STIR sequence is equally effective in suppressing fat in the neck and shoulder area.Breast cancer 76-year-old woman with advanced breast cancer. Large breast cancer is shown as a low-intensity area. Associated inflammatory process is seen around the tumor and potential axillar lymph node metastasis is well visualized. Note the absence of fat in the shoulder area.
Taro Takahara, M.D.
DWIBS neck shoulder
Breast cancer
The EPI-STIR sequence is equally effective in suppressing fat in the neck and shoulder area.
76-year-old woman with advanced breast cancer. Large breast cancer is shown as a low-intensity area. Associated inflammatory process is seen around the tumor and potential axillar lymph node metastasis is well visualized. Note the absence of fat in the shoulder area.

The DWIBS method at Tokai University

Similar to many other hospitals, brain and spine exams account for more than half of the 75 patients per day scanned by the four systems, but since the hospital does not have PET, the DWIBS method has become so popular in the various clinical disciplines (internal medicine, orthopedics, oncology and surgery) that it alone attracts 10 patients per day. Since its successful implementation two years ago, 2000 patients were scanned.

 

Another motivator for the DWIBS method is cost. While in Japan a non-contrast MRI scan is reimbursed at $300 (USD) and at $450 for a contrast (Gd-DTPA) enhanced investigation, (of which the patient pays one third and the insurance company two thirds) the current cost to the healthcare system and the patient for a PET scan is six times higher.

 

Like most new MR methods, diffusion-weighted imaging (DWI) was first applied in the brain. In the mid-1990s it became a successful method for assisting in acute stroke diagnosis. Since then, it has been found that the apparent diffusion coefficient (ADC) of tumors also is affected (reduced) due to their larger cell diameter and denser cellularity compared to normal tissues.

 

Dr. Takahara has developed a DWIBS protocol based on free breathing DWI acquisition with STIR and evaluated this method in a first group of patients with know malignancies in neck, chest or abdomen.

 

DWIBS PET
DWIBS
PET
DWIBS PET
DWIBS
PET

  DWIBS has higher resolution than PET in this comparison of a

  recurrent rectal cancer.

 

Body DWI demands high SNR and good fat suppression

Dr. Takahara's goal was to develop an MR-based technique that would give results similar to Positron Emission Tomography (PET) for evaluating lesions in the body. The direction chosen by Dr.Takahara and his colleagues was to evaluate thin-slice DWI and its MIP or MPR reconstructions.

 

Because DWI is based on the detection of random (Brownian) motion of water over very small distances, the breath-hold scan was initially considered to be the only way to avoid motion artifacts caused by the larger motion of the body's organs over the respiratory cycle. Unfortunately breath-hold scanning has SNR limitations because of its short acquisition time. This would eliminate the possibility of acquiring thin slices with sufficient SNR for a 3D MIP display; a very useful feature of the PET scanner.

The SENSE parallel imaging method is used to avoid image distortion caused by air in the lungs and intestines. Also, good fat suppression is essential, because nonsuppressed fat may obscure pathology in a rotating 3D MIP display. Fat suppression by means of SPIR and ProSet is not always robust enough in difficult areas like the neck and shoulders.

 

Dr. Takahara and his colleagues were determined to solve these issues. Tokyo-based Philips clinical scientist Marc Van Cauteren Ph.D. shared their determination.

Free-breathing and STIR provide best results

Contrary to popular belief, Dr. Takahara found that free-breathing scanning produces very good image quality. In fact, thanks to the longer scan times permitted by the free-breathing scanning method, multiple signal averages can be used, which yield high signal-to-noise ratios, so that thin slices can easily be obtained. These in turn, allow good quality MIP reconstructions.

 

The free breathing acquisition method works so well, because the signal averaging is performed on the reconstructed image and not in k-space. This "averages out" motion artifacts, a phenomenon also observed in conventional body imaging.

 

 

  23-year-old man with thymoma.The non-breath-hold scan (center) has much better SNR than

  the breath-hold scan (left) and can be used for high resolution MPR (right).

 9 mm axial image obtained in
a 25 sec. breath-hold scan. 8 mm axial image
reconstructed from a 4 mm
axial non-breath-hold scan
obtained in 7min. 5 mm sagittal image
reconstructed from 4 mm
axial non-breath-hold scan.
9 mm axial image obtained in a 25 sec. breath-hold scan.
8 mm axial image reconstructed from a 4 mm axial non-breath-hold scan obtained in 7min.
5 mm sagittal image reconstructed from 4 mm axial non-breath-hold scan.

 

 

In 2D, thick-slice, diffusion-weighted imaging experiments, the SE-EPI combined with the narrow-band SPIR pulse is reasonably successful in generating fat-suppressed images of the central nervous system or even of the body. However to meet the requirement for good fat suppression over the complete FOV associated with a large volume multislice acquisition, the Tokai research group found that STIR combined with a regular EPI sequence is far more effective.

 

 

EPI STIR This EPI-STIR image clearly shows the swollen lymph nodes around the left sub-mandibular gland (pathology unknown), without interfering fat signal from jaw or clavicle.
EPI STIR
This EPI-STIR image clearly shows the swollen lymph nodes around the left sub-mandibular gland (pathology unknown), without interfering fat signal from jaw or clavicle.

 

"Flexibility has always been the hallmark of the Philips scanner," Dr. Takahara says. "Via the standard user interface, operators can simply build their own protocols by activating parameters that are known to work well in other protocols. No complicated pulse programming software or vendor involvement is necessary to achieve this. Marrying EPI to STIR is just one example."

 

Another benefit of STIR is the attenuation of the intestinal signal. As intestinal content has a short T1, it is partially suppressed with STIR pulse. This in turn provides a less obscured image to assist in the detection of intra-abdominal lesions.

 

The DWIBS protocol

For their experiments, the Tokai group tried two different approaches. One involved the use of a SENSE Body coil, which yields excellent results. To prove the viability of the method, Dr. Takahara also used the 12-channel Peripheral Vascular coil as a whole body alternative.

 

In order to also create similarity in the appearance of the DWIBS and PET images, the Reverse Video feature is activated in the DWIBS protocol.

 

The DWIBS sequence requires a total acquisition time of approximately seven minutes.

 

 

DWIBS Fst26
DWIBS
Fst26

DWIBS of patient with malignant lymphoma

in Peripheral Vascular coil. Corresponding

coronal MIP image clearly shows swollen

lymph nodes Wardyer's ring, left sided neck,

supraclavicular, chest, mesenteric and

inguinal portions (arrows).

 

 

The EPI-STIR combination suppresses / visualizes tissue according to this table:


Suppressed tissue        Visualized normal tissue        Visualized abnormal tissue

  Vessels                             Prostate,Testes                          Tumors

  Muscle                              Endometrium, Ovary                   Abscesses

  Fat                                    Spleen

  Most Organs                      Tonsils

                                          Lymph Nodes

                                         Peripheral Nerve


 

 

Since no radiation is involved as in PET or CT, the DWIBS method may obviously be useful in the frequent follow-up studies associated with chemotherapy. Using a post-processing workstation (e.g. ViewForum), total lesion volume may automatically be calculated from the images.

 

Although not really associated with the current topic, DWIBS has also been used successfully to aid visualization of peripheral nerve disease.

 

MR neurography Diffusion-weighted MR neurography of lumbar plexus in a healthy volunteer.
MR neurography
Diffusion-weighted MR neurography of lumbar plexus in a healthy volunteer.

Important benefits

Dr. Takahara and his colleagues firmly believe in the important advantages offered by the new technique. Compared to PET it is less costly, does not involve radiation and does not require the patient to be motionless for 30 minutes. Compared to CT, there is no contrast medium or ionizing radiation. Consequently, they consider the DWIBS method an ideal tool for imaging tumors in the body and in the follow-up of patients undergoing chemotherapy.

More information:

Reference:

Takahara T, Imai Y,Yamashita T,Yasuda S, Nasu S, Van Cauteren M.

Diffusion weighted whole body imaging with background body signal suppression (DWIBS): technical improvement using free breathing, STIR and high resolution 3D display.

Radiat Med. 2004 Jul-Aug; 22(4):275-82.

 

For a pdf please see: http://www.nv-med.com/rm/pdf/20042204/275.pdf



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Best Practice
Intera 1.5T
Release 10
Abdomen, Body, Breast, Liver, Lungs, Mediastinum, Oncology, Pelvis, Prostate, Thorax, Total Body, Uterus, Women's health
 

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