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a technique of a magnitno-resonant tomography

Research carried out on Mr-system «Magnetom Espree» (Siemens Medical Systems, Germany) with an induction of a magnetic field 1,5 Tl. Taking into consideration extent of research, to patients with the expressed painful syndrome directly ahead of the scanning beginning medicamental anaesthesia that allowed to provide, first, tolerance of the patient, and, secondly, was carried out to minimise impellent artefacts.

Also before the beginning of scanning to patients recommended to empty a bladder.

Research carried out in position of the patient laying on a back a head to a magnet tunnel, before the beginning of scanning round an interest zone (from a calvaria to the hip middle) placed accepting coils: kvadraturnye coils for head and neck research and two superficial coils for a trunk. Superficial coils took places strictly one after another without applying and "free" intervals that provided a continuity of received images. Positioning of coils and packing of the patient are illustrated in a drawing 1.

Drawing 1. Placing of coils by preparation of the patient for performance MRT of an axial skeleton.

For a marking of mainframes of sections the first carried out scout images in the form of 3 sections in three planes (sagittalnoj, face-to-face and axial) with use of modified impulsive sequence HASTE (Half-Fourier Acquired Single-Shot Turbo Spin Echo). Scanning consistently carried out for 4 "departments" (a head-neck, a breast-stomach, a stomach-basin, a basin-hip) with controlled caudal shift of a table on 25 sm for each "department" and the subsequent combination of the received images.

At positioning of mainframes of sections used function of their automatic shift; thus for positioning of series DVI crossing of blocks was planned for 2 sm on a z-axis that allowed to prevent occurrence of "blind" intervals and did possible construction of multiplane reconstruction (the Drawing 2).

And

Drawing 2. A locating of series DVI on the topogram at data gathering in face-to-face () and sagittalnoj () planes.

Blocks of sections are placed so that to provide overlapping on a z-axis on 2 sm (the white finger extent of the block, the black finger - overlapping sites).

Mr-research of an axial skeleton assumed performance of 3 types of impulsive sequences: (1) DVI, (2) STIR (Short Tau Inversion Recovery), (3) Т1-ВИ turbo spin echo and gradient echo.

The diffuzionno-weighed images of all body initially received in an axial plane. In a combination with perednezadnim a direction fazovokodirujushchego a gradient it allowed to adapt a review field under the constitutional features of the patient, reduced distortsiju images, and also at maintenance of zero distance between sections allowed to reconstruct the received blocks of data in any planes (usually in orthogonal sagittalnoj and face-to-face).

Each block DVI included 40 sections in the thickness of 5 mm without distance between sections that allowed to cover a zone with extent to 20 sm on a z-axis. Thus, reception DVI of all body (from a calvaria to the hip middle) needed 5-6 consecutive blocks depending on growth of the patient.

To research applied the sequences modified an echo-planar with following parametres of data gathering: number of sections - 40, a thickness of a section - 5 mm, distance between sections - 0 mm, a review field - 45х34 sm, TR - 11,400 ms, TE - 87 ms, number of averagings - 8, a matrix - 128х128, a strip

L

Frequencies - 2056 Hz/pixel, suspension factors - 50, 900 with/mm, TI - 180 ms.

At updating of impulsive sequence for reception DVI of all body we adhered to two main objectives: maintenance of as much as possible high parity a signal/hum (SNR) and minimisation of artefacts to which impulsive sequences are rather acquisitive an echo-planar.

Unlike DVI separate organs and anatomic areas maintenance of the high permission in a section plane (i.e. a high matrix and a small field of the review) at DVI bodies was not of great importance, and even was undesirable since it was inevitably accompanied by falling of a parity a signal/hum (SNR). In particular images suffered from it with high b the factor which had major importance for revealing and the characteristic of the centres.

High value of a parity (SNR) allowed to reach a signal/hum of optimum contrast of the pathological centres against the lowered signal from not changed tissues. For maintenance of a high parity a signal/hum of 5 mm used a thickness of a section at a matrix in a direction of phase coding 128 and the maximum possible number of averagings within taken away time.

Prominent aspect of maintenance of a high parity a signal/hum was maintenance of low value of time an echo (TE) - less than 100 ms. Influence TE on a parity a signal/hum and contrast of images is illustrated in a drawing 3.

And

Drawing 3. Influence of time an echo (THOSE) on a parity a signal/hum (SNR) the diffuzionno-weighed images.

DVI with THOSE 150 ms () and 87 ms (), other parametres of data gathering are identical. The image with smaller THOSE visually shows higher SNR.

For maintenance minimum TE and levellings of an artefact of chemical shift use of high value of a strip of frequencies was expedient. However excessively high value of the given parametre were accompanied by falling of a parity a signal/hum and occurrence of artefact Najkvista in the form of duplication of images in a direction fazovo - a coding gradient. Thus, the strip of frequencies demanded the considered adaptation, application of value of an order allowed to reach 2050 Hz/pixel of necessary balance of effects of the given parametre.

As is known, for the purpose of minimisation of artefacts of chemical shift Mr - diffusion of all body it is necessary to combine with suppression of a signal from a fatty tissue. For reception of Dv-images of all body we used zhiropodavlenie on the basis of algorithm of inversion-restoration (STIR) in due course inversions 180 ms. Such combination, first, allowed to minimise the artefacts caused negomogennostju of a magnetic field, i.e. levelled artefacts from gas in lungs and an intestine lumen, from calcifications, hemorrhages and metal structures (for example, surgical clips). It also did possible reception of images such difficult for MR zone visualisation as a thorax, and also essentially reduced number of artefacts at visualisation of the bottom department of a neck, area of shoulders, mammary glands and feet.

Secondly, combination ДВИ-STIR allowed to reach homogeneous suppression of a signal from a fatty tissue at use of a big field of the review, and also was characterised by higher contrast of the pathological centres against a low signal from the background not changed tissues than alternative frequency-selective zhiropodavlenie (the Drawing 4).

And

Drawing 4. Example DVI with various algorithms of suppression of a signal from a fatty tissue: and - frequency-selective zhiropodavlenie, - Short Tau Inversion Recovery (STIR).

On images with frequency-selective zhiropodavleniem there are expressed peripheric artefacts from insufficient suppression of a signal from a fatty tissue (finger), on images ДВИ+STIR depression of a signal from a fatty tissue is more homogeneous.

At reception DVI we used two factors of suspension (b - the factor). The smaller b-factor made 50 with/mm and was used for reception of images with suppression of a signal from moving blood, in the rest contrast such skanov differed from Т2-ВИ with suppression of a signal from a fatty tissue a little. Maximum b the factor made 900 with/mm, that allowed, in - the first, effectively to suppress a signal from the background not changed tissues, in - the second, contrastly to visualise sites of an edema, pathological infiltration and a neoplasm of various localisation, and, at last, to support high enough SNR, after all the above value b the factor, the less signal will be present on images. Besides, the maximum value b 900 with/mm allowed to keep comprehensible time of data gathering since the more maximum b the factor, the is required to more time for reception of images.

Use of two b-factors allowed to calculate a measured diffusion coefficient (IKD) which represents its quantitative equivalent (the Drawing 5).

And in

Drawing 5. An example of reception DVI with cards of a measured diffusion coefficient in an axial plane.

Images are executed at identical level: DVI with the b-factor 50 with/mm2 () are characterised by the contrast similar on Т2-ВИ with suppression of a signal from a fatty tissue, on DVI with the b-factor 900 with/mm () effective suppression of a signal from not changed tissues becomes perceptible and there is more contrast a centre in a body of a vertebra (marksman). On card IKD () contrast directly is defined by rate of Brown movement in tissues of molecules of water and differs from that on DVI.

IKD counted for everyone vokselja images and represented in the form of the parametrical cards automatically generated MR by system on the basis of calculation difficult bieksponentsialnoj of dependence. Measurements IKD were made manually, for this purpose on DV images chose a zone of interest which then was copied on card IKD.

After reception of all blocks DVI to them united in a uniform file, for this purpose, and also in order to avoid regional distortsii images, at planning of series it was necessary to be convinced that consecutive blocks are blocked not less than on 2 sm on a z-axis. From such file then again received multiplane reconstruction with thickness of a section of 5 mm and images of the maximum intensity (MIP). For convenience of interpreting secondary images also represented with inversion of a scale grey (the Drawing 6).

Mr-research of an axial skeleton was a part of report MRT of all body which besides DVI included Т1-ВИ and STIR in axial and sagittalnoj planes, parametres of impulsive sequences are resulted in table 3.

Exact anatomic localisation for DVI defined on STIR in an axial plane since this sequence unites in itself to high contrast, high enough rate of the data gathering, homogeneous suppression of a signal from a fatty tissue at a big field of the review and low sensitivity to artefacts. Without anatomic images to interpret DVI in aspect of localisation of the centres difficult enough since this sequence is referred on achievement of as much as possible high parity a signal/hum to the detriment of spatial detailed elaboration.

And

In

Drawing 6. An example postprotsessingovogo representations DVI of an axial skeleton.

MIP in sagittalnoj () and face-to-face () planes with inversion of a scale grey, MPR in a face-to-face plane.

STIR received in the form of consecutive blocks of sections in an axial plane. For a breast and a stomach data gathering spent with adaptation to breath by means of the trigger established on the top point of the right dome of a diaphragm. For other anatomic areas data gathering carried out without a breath drawing.

For research Т1 of contrast report MRT of all body included Т1-VI gradient echo with two value THOSE (2,2 ms and 4,4 ms), that allowed to receive for one data gathering besides traditional Т1-ВИ with an antiphase water-Adeps. The artefact of chemical shift arising on such images, allowed to differentiate authentically the centres rekonversii a red osteal brain from pathological infiltrates (the Drawing 7).

And

And in

Drawing 7. Application Т1-ВИ (gradientnoe an echo in an antiphase water-Adeps) in

Visualisation of a red osteal brain.

Local rekonversija a red osteal brain (marksman) against its diffusive fatty replacement at the patient with a serious anorexia. The red osteal brain is characterised by a signal of low intensity on standard Т1-ВИ (), thus at the expense of an artefact of chemical shift and suppression of a signal from intracellular Adeps it becomes sharply hypointensive on Т1-VI in an antiphase (); on STIR () a signal from a red osteal brain weakly hyperintensive.

Images in Т1-VI received in an axial plane in the form of consecutive blocks, covering all zone of data gathering (from a calvaria to the hip middle); for a breast and a stomach data gathering was spent on a breath holding, for other areas of a body - on free breath.

After the first application of report MRT of all body in the form of ДВИ+STIR+Tl-VI with data gathering only in an axial plane on small group of volunteers became obvious, that this plane of data gathering has not enough for an adequate estimation of the spine column which is a frequent target of metastasises. In an axial plane it is difficult to differentiate intervertebral disks and switching plates of bodies of vertebra, and localisation of focal changes in an osteal brain of vertebra concerning these anatomic structures is of great importance for definition of the nature of changes.

For overcoming of this disadvantage we have included in report STIR and Tl-ВИ turbo spin echo in sagittalnoj planes with two "departments" of data gathering: the first department assumed reception of images cervical and verhnegrudnogo backbone departments, and the second - nizhnegrudnogo and lumbosacral departments.

The generalised parametres of the developed technique vysokopolnoj MRT an axial skeleton are presented in table 3.

Thus, we had been developed technique MRT of an axial skeleton with the Mr-diffusion application, allowing to tap and characterise focal changes of an osteal brain.

The scanning report includes reception DVI with two factors

L

Suspensions b 50, 900 mm/with with cards IKD allowing quantitatively to estimate change of diffusion of molecules of water.

Postprocessing DVI in the form of MIP and MPR with inversion of a scale of the grey gives possibility of the fast review of all file of the received data with high contrast of the pathological centres.

Besides DVI the report of research of an axial skeleton of patients assumes reception Tl-ВИ and STIR in axial and sagittalnoj planes that specifies anatomic localisation and morphological substrate of the taped changes.

Table 3

Technique of Mr-research of an axial skeleton

scout DVI aks STIR

aks

^-VI

aks

STIR

Sagas

^-VI

Sagas

Number of sections 3 40 35 24 13 15
Thickness of a section, mm 7.0 5,0 6,0 6,0 4,0 4,0
Distance between sections, mm 10 0 1,2 1,2 0,4 0,4
Review field, mm 340х340 450х337 380х380 380х320 300х300 300х300
TR, ms 1500 11400 3800 105 4000 562
THOSE, ms 95 87 72 2,31

4,83

37 9,7
Number

Averagings

1 8 1 1 2 2
Matrix 256х256 128х128 320х224 256х256 256х256 256х256
Strip of frequencies, G ts/pixel 399 2056 284 390 191 199
Turbo the factor 256 96 32 - 11 3
Direction

fazovo

The coding

Gradient

Spered and back In front

Back

In front

Back

In front

Back

From above

Downwards

From above

Downwards

Factors

Suspensions

L

(b), from mm

- 50

900

- - - -
Suppression of a signal from a fatty tissue - + + - + -
Data gathering time 0:15 3:37 1:16 0:39 3:18 1:34
General time of data gathering ~45 mines

2.3.

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A source: PAVLOV Denis Gennadievich. HIGH-FIELD MAGNETIC-RESONANT TOMOGRAPHY WITH THE APPLICATION OF MR-DIFFUSION IN DIFFERENTIAL DIAGNOSTICS OF METASTATIC BONE MARROW. Thesis for the degree of candidate of medical sciences. SAINT-PETERSBURG 2014. 2014

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