1. Philips Achieva Mri Diagnostic Imaging Manual Do Mundo
2. Philips Achieva Mri Diagnostic Imaging Manual Muscle

PURPOSE: To introduce and validate an automatic segmentation method for the discrimination of skeletal muscle (SM), and adipose tissue (AT) components (subcutaneous adipose tissue SAT and intermuscular adipose tissue IMAT) from T1-weighted (T1 -W) magnetic resonance imaging (MRI) images of the thigh. MATERIALS AND METHODS: Eighteen subjects underwent an MRI examination on a 1.5T Philips Achieva scanner. Acquisition was performed using a T1 -W sequence (TR = 550 msec, TE = 15 msec), pixel size between 0.81-1.28 mm, slice thickness of 6 mm. Bone, AT, and SM were discriminated using a fuzzy c-mean algorithm and morphologic operators. The muscle fascia that separates SAT from IMAT was detected by integrating a morphological-based segmentation with an active contour Snake. The method was validated on five young normal weight, five older normal weight, and five older obese females, comparing automatic with manual segmentations.

RESULTS: We reported good performance in the extraction of SM, AT, and bone in each subject typology (mean sensitivity above 96%, mean relative area difference of 1.8%, 2.7%, and 2.5%, respectively). A mean distance between contours pairs of 0.81 mm and a mean percentage of contour points with distance smaller than 2 pixels of 86.2% were obtained in the muscle fascia identification. Significant correlation was also found between manual and automatic IMAT and SAT cross-sectional areas in all subject typologies (p.

Results For the GE 1.5 T MRI system, the MRI scanner‐reported SAR value was 1.58 W kg ‐1 and the measured SAR value was 1.38 W kg ‐1. For the Philips 1.5 T MRI scanner, the MRI system‐reported SAR value was 1.48 W kg ‐1 and the measured value was 1.39 W kg ‐1. For the Siemens 3 T MRI system, the reported SAR value was 2.5 W kg ‐1 and the measured SAR value was 1.96 W kg ‐1. For two Philips 3 T MRI scanners, the reported SAR values were 1.5 W kg ‐1 and the measured values were 1.94 and 1.96 W kg ‐1. The percentage differences between the measured and reported SAR values on the GE 1.5 T, Philips 1.5 T, Siemens 3 T, and Philips 3 T were 13.5, 6.3, 24.2, 25.6, and 26.6% respectively. 1 Introduction Magnetic resonance imaging (MRI) generates images for medical diagnoses of diseases using a static magnetic field and time‐varying electromagnetic fields generated by a radiofrequency (RF) transmit coil and x‐, y‐, and z‐gradient coils, respectively. These time‐variant electromagnetic fields induce electric currents and voltages in the conductive human body when positioned inside an MRI scanner.

The eddy currents induced by the time‐varying electromagnetic fields during an MRI scan can cause undesired heating of patients due to the deposition of RF power into the body, and this is a significant safety concern. It is thus necessary to determine the RF energy absorbed by the body in terms of the specific absorption rate (SAR). According to International Electrotechical Commission (IEC), the SAR value should be limited to 3.2 W kg ‐1 for the head and 4.0 W kg ‐1 for body applications for durations of 6 min. Similarly, the Food and Drug Administration (FDA) of the United States requires that the SAR should be less than 4 W kg ‐1 when averaged over the entire body for 15 min and 3 W kg ‐1 for the head for 10 min. The risk of hyperthermic tissue damage is relatively serious for neonates and for children who cannot communicate verbally, as well as for patients who have insensate limbs and those who are under anesthesia during the MRI scan. Commercial MRI scanners provide an estimated SAR level for each scan; this level is calculated from the RF waveforms and sequence parameters, system calibration, Q factors and loading of the RF transmit coil, etc.

The SAR calculation assumes certain average parameters, which in reality can vary from scanner to scanner and may change over time. Incorrect manufacturer‐reported SAR values have been acknowledged for clinical MR imaging systems. For example, one study found a scanner overestimated the SAR by up to 2.2 folds. Even before the highest allowed SAR level has been reached, a patient's sweating during an MRI can raise concerns of possible overheating. On the other hand, overestimating the SAR can prevent certain important scans to be run on a patient.

Philips Achieva Mri Diagnostic Imaging Manual Do Mundo

It is also conceivable that a malfunction in the quadrature RF transmit coil can generate RF with higher levels in the counter rotating component, resulting in higher than expected power deposition levels. Direct estimation of SAR values independent of the level calculated by MRI scanners is therefore desirable. Numerical calculations of RF energy deposition levels have been performed to predict SAR levels in anatomical models consisting of homogeneous cylinders, spheres, or in head models., - There is a large range of variability in SAR levels for different pulse sequences.

May 4, 2017 - Magnetic resonance imaging (MRI) generates images for medical. Five MRI scanners: an Achieva 1.5 T (Philips Healthcare), a Signa Excite. The apparent diffusion coefficient within an ROI (red) which was manually placed. Philips Achieva 1.5T Tech Specs - Download as PDF File (.pdf), Text File (.txt) or read online. Diffusion weighted imaging: Standard Functional MRI: Optional Spectroscopy (nuclei of interest): Optional MRA: Standard Time of flight:. The Philips MRI Customer Experience team to leading the Philips MRI business, I will. MRI, Philips Healthcare. MR-OR setup, the MR system can be used for regular diagnostic imaging when not being used in surgery. With a triple-room OR-MR-OR setup, two ORs can utilize.

Global and local SAR measurements at different B 0 magnetic field strengths and measurements of exposure to different RF coils have been conducted. However, direct measurement of RF heating in a clinical setting has not been an easy task. Temperature measurement using optical thermometry only yields values in few spatial points. In the present study, we demonstrate the measurement of SAR of a human torso phantom using diffusion MRI in clinical MRI systems from different vendors.

2.A MRI scanners SAR levels were measured on five MRI scanners: an Achieva 1.5 T (Philips Healthcare), a Signa Excite 1.5 T (GE Healthcare), a Magnetom Verio 3 T (Siemens Healthcare), and two Achieva 3 T (Philips Healthcare) systems. SAR values for three different MRI sequences with SAR values (1.48, 1.5, 1.58, and 2.5 W kg ‐1 nominal values as reported by MRI scanners) were measured on various scanners at two discrete magnetic field strengths. Image acquisition parameters are summarized in Table. The RF excitation power was transmitted by an integrated RF body coil (Multi‐transmit mode = “NO” at Philips 3 T).

A four‐ or eight‐channel body array coil was employed as a receive coil in this study. Image sequence T1w TSE T1 TIRM T2w TSE TR/TE ms 8/9.3 4710/110 TI ms n/a 220 n/a Field of view mm 2 400 × 400 400 × 400 400 × 400 No. Of slices 10 8 10 Slice thickness mm 6 6 6 Acquisition matrix 400 × 400 256 × 256 200 × 154 (reconstructed to 400 × 400) Voxel size mm 3 1 × 1 × 6 1.56 × 1.56 × 6 1 × 1 × 6 Slice orientation Transverse Transverse Transverse Phase‐encoding direction AP AP AP NSA 2 1 4 Total scan time (GE 1.5 T/ Philips 1.5 T) 5 min 12 s/4 min 56 s 4 min 18 s 4 min 23 s Parallel imaging method No GRAPPA for Siemens 3 T No Bandwidth Hz/pixel (GE 1.5 T/ Philips 1.5 T) 260/290 260 334.

2.B Human torso phantom morphology A cylinder‐shaped human torso phantom (50 cm (L) × 43 cm (W) × 28 cm (H)) was constructed on the basis of U.S. Anthropometric reference data (Fig. The airtight plastic phantom container (15 mm thickness) was filled with a volume of approximately 16.6 L of a hydroxy‐ethyl cellulose (HEC) gelled‐saline solution consisting of 25.7 g of NaCl, 514.6 g of HEC powder, and 16.6 L of distilled water, simulating human tissue, as described in the American Society of Testing Materials (ASTM) International standard method for SAR measurements.

Phantom morphology mimics the shape of the human torso. The gel thermal properties (thermal diffusivity = 1.4 × 10 ‐7 m 2s ‐1 and heat capacity = 4156 J/(kg°C)) were measured with a thermal property analyzer (KD2, Decagon Devices Inc., Pullman, WA, USA). The electric conductivity ( σ = 0.48 ± 0.04 S m ‐1 at 64 MHz and 0.49 ± 0.04 S m ‐1 at 128 MHz) and relative electric permittivity ( ε r = 76.48 ± 3.98 at 64 MHz and 76.22 ± 4.12 at 128 MHz) of the gel solution were measured using a dielectric assessment kit (DAK‐12, SPEAG Ltd., Zurich, Switzerland). A vacuum was created in the phantom container to eliminate air bubbles in the gel phantom. 2.C Independent SAR assessment using diffusion measurement Four optic fiber temperature sensors (OFS, Neoptix Inc., Quebec, Canada) were placed at the periphery of the gel phantom at 28°C to certify that there was minimal heat loss to the environment during the measurements (Fig. We measured the initial temperatures of the sensors positioned in the phantom and the time it took to reach equilibrium with the environment.

We considered that thermal equilibrium has been reached when the difference between temperatures measured by the sensors in the phantom and temperature inside the magnet bore was less than 0.1°C. Location of four optic fiber temperature sensors in the phantom periphery, used to measure the initial temperatures of the phantom and the time taken to reach equilibrium with the environment. On each MRI scanner, the heating of the gel phantom caused by a high SAR sequence was assessed by the changes in the mean diffusivity (MD) value, before and after running the high SAR image sequence. A region‐of‐interest (ROI)‐based MD calculation was performed for the SAR measurements. In the ROI‐based quantification, the average signal intensity within the ROI as shown in Fig. For the b = 0 image and each high b diffusion‐weighted image was measured first.

Using these values, a diffusion tensor was calculated, and MD value was obtained. The water diffusion coefficient in the gel was practically identical to that of free water, and the diffusion coefficient (D) was very sensitive to the temperature (T)., The temperature was calculated using the following equation. The apparent diffusion coefficient within an ROI (red) which was manually placed on the periphery of the phantom was quantified using a set of diffusion‐weighted images.

Verification of temperature changes obtained by the diffusion coefficients using Eq. Was performed by comparison to those measured by four optic fiber temperature sensors positioned as in Fig. The mean diffusion coefficients within each ROI which were manually drawn around the temperature sensors were calculated using software written in IDL 8.4 (IDL Research Systems Inc., Boulder, CO, USA) before and after the high SAR image sequence at 3 T.

The MD value was the average over 14 pixels within the ROI in one slice showing the tip of the sensors. For each study, the phantom was placed in the scanner room for at least 24 hr to establish thermal equilibrium with the environment. The same phantom weight (18 kg) was entered into the MRI system at registration. First, the SAR value induced by the diffusion tensor imaging (DTI) scan was measured for the torso phantom on each MRI scanner using repeated DTI scans.

Second, in order to measure the SAR value caused by the high SAR sequences, an axial DTI scan was initially conducted, followed by several minutes of high SAR scan. The DTI scan was then repeated. The scanner‐specific DTI acquisition parameters are listed in Table. Auto‐shim was utilized in all studies.

Philips Achieva Mri Diagnostic Imaging Manual Muscle

The mean diffusivity within a ROI which was manually placed at the periphery of the phantom was evaluated for each DTI scan using software written in IDL 8.4 (Fig. ), and the temperature change derived from the difference between the MD maps was estimated (Fig. The standard error of the mean diffusivity for the ROI ranges from 0.0005 × 10 ‐3 to 0.0006 × 10 ‐3 mm 2 s ‐1 for the 5 scanners based on repeated measurements. (2) Here, C p (= 4.18 kJ/(kg°C)) is the specific heat of the phantom, ΔT is the temperature change in °C, and TA is the acquisition time of the pulse sequence. The first term on the right‐hand side is the heating from the DTI sequence, and the second term on the same side represents the heating from the high SAR sequence under investigation. One SAR measurement was performed in one MRI session, and then the phantom was placed in the scanner room for one day to reach thermal equilibrium with the environment. SAR measurements were repeated at least 10 times for each MRI scanner and the mean and standard deviation (SD) were calculated.

Percentage differences between the measured mean and reported SAR values on the MRI scanners were calculated. Temperature inside magnet bore = 22.8 ± 0.6°C Sensor No.

Initial temperature Final temperature Time to equilibrate with the environment OFS#1 28.4 ± 0.5°C 22.7 ± 0.6°C 4 hrs 08 min OFS#2 28.3 ± 0.6°C 22.8 ± 0.5°C 4 hrs 02 min OFS#3 28.3 ± 0.6°C 22.8 ± 0.6°C 4 hrs 07 min OFS#4 28.2 ± 0.5°C 22.7 ± 0.6°C 4 hrs 11 min Table shows temperatures obtained by the diffusion coefficients and measured using four optic fiber temperature sensors in the phantom on one of 3 T MRI scanners. The measured temperature changes by the two methods agreed very well, with the difference between these two methods ranging from 6% to 9%.