Posted by
Fred Damen on
Aug 06, 2018; 2:52pm
URL: http://imagej.273.s1.nabble.com/DICOM-voxel-value-tp5021048p5021051.html
Greetings,
Thanks, but why is this being done? And more importantly how am I supposed to
get the raw stored value in the DICOM dataset?
Note: the positive values in both the signed and unsigned integers are
logically and physically the same, i.e., no conversion. The negative signed
values are physically the same as the large positive (>32768) unsigned values,
conversion depends on why the logical and physical representations are
different. In the case of MRI DICOM the values are positive and <10K, so no
conversion (either signed/unsigned), thus no header values for conversion.
The way the status line displays these values suggests to me that the raw and
converted values are known to ImageJ. I'd prefer not to have to guess as to
how the voxel values were manipulated.
Thanks,
Fred
On Mon, August 6, 2018 2:25 am, Herbie wrote:
> Good day Fred,
>
> this effect maybe due to signed and unsigned 16bit gray-scale.
>
> 2^15 = 32768;
> 32768 + 4691 = 37359;
>
> HTH
>
> Herbie
>
> ::::::::::::::::::::::::::::::::::::::::
> Am 06.08.18 um 05:51 schrieb Fred Damen:
>> Greetings,
>>
>> When dealing with MRI DICOM datasets I am getting what I consider to be an
>> incorrect value when fetching the voxel value using Java methods
>> ImageProcessor::get(x,y) or getf(x,y). Case in point, when the status line
>> on
>> the main ImageJ window reads "... value = 4691.00 (37459)", the value
>> returned
>> by get/getf is 37459 and not the correct value of 4691.
>>
>> What is this second value and how do I fetch the correct value?
>>
>> These DICOM datasets should not contain voxel intensity scaling, and, the
>> list
>> of tag/values produced on the 'Info' page for one of the slices does not
>> contain the tags: Rescale intercept, (0028|1052), and rescale slope
>> (0028|1053). The raw data stored in the files are 16 bit signed integers:
>> 0028,0100 Bits Allocated: 16
>> 0028,0101 Bits Stored: 16
>> 0028,0102 High Bit: 15
>> 0028,0103 Pixel Representation: 1
>> The values are always below 10K.
>>
>> The ImageJ image summary incorrectly indicates that the dataset is scaled:
>> Calibration function: y = a+bx
>> a: -32768.000000
>> b: 1.000000
>>
>> but this scaling would not produce the second value on the status line given
>> the correct value.
>>
>> Thanks in advance,
>>
>> Fred
>>
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http://imagej.nih.gov/ij/list.html>>
>
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