[Insight-users] Urgent: Strange dicom imageIO

[Markus Weigert]

Hi Wilfred, hi Mathieu,

both series, the original and the written series have the same values
for Modality Rescale Slope = 1.0 and  Modality Rescale Intercept element 
= -1024.
So I don't know if the problem are these tags, though I didn't change 
anything in the
data dictionary.
I will have to check my code again.

Regards,
Markus



----- Original Message ----- 
From: Wilfred Rosenbaum
To: Markus Weigert
Sent: Thursday, May 11, 2006 2:22 AM
Subject: Re: [Insight-users] Urgent: Strange dicom imageIO


Hi Markus,

I"ll bet the original image had a Modality Rescale Slope element with value 
1.0 and a Modality Rescale Intercept element with value -1024. (I think that 
the DICOM tags of these elements are (0028,1052) and (0028,1053) but this is 
just off the top of my  head so I could be wrong ). This is pretty common 
for CT images. These elements, if present, specify a linear transformation 
that is to be performed on the stored pixel values of the image to convert 
them to Hounsfield units. I suspect that the first time that you examined 
the pixel values they did not have the Modality Rescale transformation 
applied, but after you wrote the series to inspected the values again the 
pixel values did have the Modality Rescale transformation applied.

Cheers,
Wilf.

----- Original Message ----- 
From: "Mathieu Malaterre" <mathieu.malaterre at kitware.com>
To: "Markus Weigert" <m.weigert at fz-juelich.de>
Sent: Wednesday, May 10, 2006 11:32 PM
Subject: Re: [Insight-users] Urgent: Strange dicom imageIO


> Markus Weigert wrote:
>> Hi,
>>
>> today I encountered a strange  problem with dicom ImageIO:
>>
>> After reading a dicom series of  CT - files and displaying the volume 
>> with
>> GLTwoImageSliceView (from insight applications), everything is fine.
>> The range of the values is -1024 up to 3071, just as it should be.
>>
>> But after writing the serie again to dicom slices and reading these 
>> slices,
>> the range is now -2048 to 2047, so there seems to be a shift.
>> I don't understand this, because I didn't change anything in the 
>> MetaDataDictionaryArray.
>>
>> Has anybody an idea what could cause this shifting of image values?
>
> Markus,
>
> Do you have rescale intercept / slope in your input DICOM file ?
>
> Mathieu