Post by John KatsaridasPost by Doug SluisNote that Pixel Spacing (0028,0030) does not apply to all image IOD's.
E.g. it is not a valid attribute in ultrasound.
- doug
Post by John KatsaridasIn the dicom format, is Pixel Spacing (0028,0030) the distance in
millimeters
Post by Doug SluisPost by John Katsaridasbetween two pixels or is it the number of pixels per millimeter?
Thanks.
Pixel Spacing (0028,0030) :Physical distance in the patient between
the center of each pixel, specified by a numeric pair - adjacent row
spacing (delimiter) adjacent column spacing in mm.
Imager Pixel Spacing (0018,1164) :Physical distance measured at the
front plane of the Image Receptor housing between the center of each
pixel. Specified by a numeric pair - row spacing value (delimiter)
column spacing value - in mm. In the case of CR, the front plane is
defined to be the external surface of the CR plate closest to the
patient and radiation source.
I don't really understand what "Pixel Spacing" and "Imager Pixel
Spacing" mean. I have a DICOM from TROPHY. It doesn't have "Pixel
Spacing" tag, but it has "Imager Pixel Spacing" tag. I want to know
the length(in mm) between Point_A and Point_B. Cound I calculate the
length using "Imager Pixel Spacing"?
dLen := Sqrt(Sqr((StartPoint.X - EndPoint.X) / * fHPixelSize ) +
Sqr((StartPoint.Y - EndPoint.Y) / * fVPixelSize));
fVPixelSize / fHPixelSize => (Imager Pixel Spacing) row spacing value
/ column spacing value
Imager pixel spacing was created as an alternative to pixel spacing,
defined as the distanced between adjacent pixels IN THE PATIENT, for
projection radiography. In Imaging Pixel Spacing, the attribute refers
to the distance between pixels on the sensor. In a perfect world,
xrays hitting the imager sensor will be parallel or so close to
parallel so as not to make a significant difference; but with some
technologies, CR in particular, one doesn'
t really know what the geometry of the x-ray collimater is with the
sensor. So, the attribute is expressed in the dimension of the sensor
(or both the sensor and the image). Your formula is fine but you might
want to note the possibility of distance errors for situations where
the geometry of the imaging context is such that there is a
significant difference between the pixel spacing on the sensor and
distance between pixels in features imaged in the patient.