(19)
(11)EP 0 133 722 B1

(12)EUROPEAN PATENT SPECIFICATION

(45)Mention of the grant of the patent:
23.11.1988 Bulletin 1988/47

(21)Application number: 84201111.6

(22)Date of filing:  30.07.1984
(51)International Patent Classification (IPC)4G01N 24/04, G01N 24/08

(54)

Phantom for NMR apparatus

Eichkörper für magnetischen Kernresonanzapparat

Corps de référence pour un appareil à résonance magnétique nucléaire


(84)Designated Contracting States:
DE FR GB NL

(30)Priority: 01.08.1983 NL 8302721

(43)Date of publication of application:
06.03.1985 Bulletin 1985/10

(73)Proprietor: Philips Electronics N.V.
5621 BA Eindhoven (NL)

(72)Inventors:
  • Meyer, Albertus Cornelis
    NL-5656 AA Eindhoven (NL)
  • Tuithof, Hans Hermanus
    NL-5656 AA Eindhoven (NL)
  • Mulder, Jacobus
    NL-5656 AA Eindhoven (NL)

(74)Representative: Scheele, Edial François et al
INTERNATIONAAL OCTROOIBUREAU B.V. Prof. Holstlaan 6
5656 AA Eindhoven
5656 AA Eindhoven (NL)


(56)References cited: : 
EP-A- 0 042 256
EP-A- 0 106 551
GB-A- 2 043 914
EP-A- 0 105 220
GB-A- 2 041 537
  
  • NUCLEAR MAGNETIC RESONANCE (NMR) IMAGING, edited by C.L. PARTAIN et al., no. 33, 1983, pages 436-445, W.B. Saunders Company, Philadelphia, USA; N.J. SCHNEIDERS et al.: "Phantoms for NMR image analysis"
  
Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention).


Description


[0001] The invention relates to a phantom for NMR imaging apparatus, comprising a plastics body which is provided with holes which are to be filled with a contrast medium for NMR measurements.

[0002] A phantom of this kind is known from a book Nuclear Magnetic Resonance imaging, edited by Partain e, o, by N. J. Sneiders et al, pages 436-445, Nr. 33 (1983), "Phantoms for NMR image analysis". A phantom for NMR imaging, comprising a plastics form filled with a contrast medium is known from GB-A-2043914.

[0003] A phantom described therein is made of plexiglass and is provided with a plurality of holes of various diameters, some holes of the same diameter being arranged in a corresponding row at a uniform distance from one another which equals the diameter of the hole. The holes may be filled with water, with a suitable additive or with another so-called contrast medium such as vaseline.

[0004] A phantom of this kind is not optimally suited to the derivation of image information, notably concerning spatial resolution, direction-dependent imaging quality, linearity of the image and the like.

[0005] It is an object of the invention to mitigate these drawbacks; to achieve this, a phantom of the described kind in accordance with the invention is defined and characterized in claim 1.

[0006] When such a phantom is used for measuring the imaging qualities of the apparatus, information as regards the spatial resolution, the linearity of the image, the sensitivity etc. can be obtained in a direct manner.

[0007] A preferred embodiment of the phantom comprises a cylindrical body of, for example plastics which is divided into several, for example from 6 to 12 segments, in each of which there are provided at least a few series of holes which are situated along radial lines. The size of these holes which are preferably situated at a distance from one another which, as before, equals the transverse dimension of the hole in the line direction, differs from one segment to another. When such a phantom is used, the spatial resolution of the apparatus can be read directly from the image of the phantom. By rotating the phantom about the cylinder axis, the homogeneity of the resolution can also be checked.

[0008] Some preferred embodiments in accordance with the invention will be described in detail hereinafter with reference to the drawing. Therein:

Figure 1 shows a phantom which is divided into segments and which is notably suitable for the measurement of spatial resolution,

Figure 2 shows a phantom for sensitivity measurements.



[0009] As is shown in Figure 1, a phantom in accordance with the invention which is particularly suitable for the measurement of spatial linearity of the image comprises a cylinder 1 which is made of plastics and which, in this case, is round; the structure of the phantom is preferably chosen so that interference with a line pattern in the display system is avoided; consequently, preferably 6 or 12 segments are chosen. The Figure shows a division into six segments A-F. In each of the segments there is provided a regular pattern of holes 3 which are arranged at least partly along straight lines. These holes may be filled with a high-contrast medium for NMR measurements, for example aqueous solutions, vaseline, etc. The holes in a first segment A are respectively arranged along the directions of the lines, for example at a distance of 6 mm from one another, the transverse dimensions of the holes, measured along the line, preferably being equal to the spacing between two successive holes. Each of the other segments is provided with holes which have the same size for that segment and also the same spacing, for example in the sequence 4, 3, 3, Hand 1 mm. Also feasible is a spacing sequence which increases by a factor -V2- from one segment to another. The phantom as a whole has, for example a diameter of 20 cm for head measurement apparatus and a diameter of 40 cm for body measurement apparatus, its thickness being, for example from 5 to 10 cm. In a preferred embodiment, the block is composed of exchangeable segments so that the range of spatial frequencies represented by the holes can be adapted by the exchange of one or more segments, for example, by the replacement of the 6 mm segment by, for example, a 0.6 mm segment. The supporting material of the phantom is preferably a plastics which produces an extremely small NMR signal in comparison with the filler material in the holes, for example because of the very short relaxation times for the spin resonances therein. Some comparatively large holes 8 are preferably provided for positioning the phantom with respect to an object slice to be measured. One of these holes preferably extends from a first end face of the phantom to approximately half the axial height thereof, a second hole extending from an opposite end face again to half the axial height.

[0010] Figure 2 shows a phantom which is particularly suitable for sensitivity measurements; a body 21 is again divided into segments which differ only as regards thickness, for example 12 segments with a thickness difference for each step of approximately 8%. The Figure shows a phantom comprising 6 segments a to f, each of which is filled with or consists of a material which produces a resonance signal which can be suitably measured. Measurements performed on such a phantom provide a direct insight into the system linearity. A particular embodiment of this phantom comprises only two segments, each of which forms a semi-circle, the thickness difference being, for example approximately 1 mm. The response of the apparatus to a step function can be measured by means of this phantom.

[0011] Different properties of each of the described phantoms can also be combined in one phantom. For example, a phantom can be constructed so as to comprise a radial arrangement of, for example 12 rows of holes whose diameter decreases in the direction of the centre of the phantom, for example, in the sequence 20,12, 8, 5, 3, 2,1 z and 1 mm. The holes in the twelve successive radial lines have a correspondingly different depth, for example in a sequence in which the depth increases from 0.50 to 3.25 mm in steps of 0.25 mm.


Claims

1. A phantom for NMR imaging apparatus, comprising a plastic body which is provided with holes which are to be filled with a contrast medium for NMR measurements, characterized in that the body is divided into segments each of the segments being provided with a pattern of holes, the cross-sections as well as the mutual spacings of the holes being similar in each segment, but different for each different segment.
 
2. A phantom as claimed in claim 1, characterized in that the thickness of subsequent segments varies according to an arithmetical progression.
 
3. A phantom as claimed in claim 1, characterized in that it comprises two semi-circular segments.
 


Ansprüche

1. Eichkörper für Kernspinresonanzapparat mit einem Kunststoffkörper, der Hohlräume enthält, die mit einem Kontrastmittel für Kernspinresonanzmessungen gefüllt werden müssen, dadurch gekennzeichnet, daß der Körper in Kreisabschnitte verteilt ist, die mit je einem Hohlraummuster versehen sind, wobei sowohl die Durchschnitte als auch die gegenseitigen Abstände zwischen den Hohlräumen in jedem Kreisabschnitt gleich sind, sich jedoch von denen in jedem anderen Kreisabschnitt unterscheiden.
 
2. Eichkörper nach Anspruch 1, dadurch gekennzeichnet, daß die Dicke folgender Kreisabschnitte entsprechend einer arithmetischen Reihe verändert.
 
3. Eichkörper nach Anspruch 1, dadurch gekennzeichnet, daß er zwei Halbkreisabschnitte enthält.
 


Revendications

1. Corps de référence pour appareil d'imagerie par RMN, comprenant un corps en matière plastique qui est muni de trous qui sont à remplir d'un agent de contraste pour les mesures par RMN, caractérisé en ce que le corps est divisé en segments, chacun des segments étant muni d'un motif de trous, les sections transversales de même que les distances mutuelles des trous étant semblables dans chaque segment, mais différentes pour chaque segment différent.
 
2. Corps de référence suivant la revendication 1, caractérisé en ce que l'épaisseur des segments successifs varie suivant une progression arithmétique.
 
3. Corps de référence suivant la revendication 1, caractérisé en ce qu'il comprend deux segments semi-circulaires.
 




Drawing