How do I read a DICOM tag within another tag with ITK?

I'm using ITK to read a DICOM file, calling

dicomIO->GetValueFromTag(...)

to read a tag value. This works fine for tags like "300a|011e" (gantry angle). The problem comes trying to read tag "0018|0060" which is embedded inside "3002|0030".

If I use GetValueFromTag for "3002|0030" I read back an empty string as "3002|0030" is exposure sequence and has no value. How do I read tags within tags with ITK? Looking through the ITK documentation I can't see any way to do this?

Apparently you can't use ImageIOType to read sequences from DICOM, instead you have to use GDCM.

#include "gdcmReader.h"
#include "gdcmImage.h"
#include "gdcmDataElement.h"
#include "gdcmTag.h"

using namespace gdcm;

bool readGDCMTags(std::string filename, float &kvp)
{
    Reader reader;
    reader.SetFileName(filename.c_str());
    reader.Read();

    File &file = reader.GetFile();
    DataSet &ds = file.GetDataSet();

    const Tag tag(0x3002, 0x0030);
    const Tag subTag(0x0018, 0x0060);

    const DataElement &seq = ds.GetDataElement(tag);

    SmartPointer<SequenceOfItems> sqi = seq.GetValueAsSQ();

    assert(sqi->GetNumberOfItems() == 1);

    Item &item = sqi->GetItem(1);

    DataSet &subds = item.GetNestedDataSet();

    if (!subds.FindDataElement(subTag))
    {
        return false;
    }

    const DataElement &de = item.GetDataElement(subTag);

    const ByteValue *value = de.GetByteValue();

    char *buffer;

    VL vl = value->GetLength();
    uint32_t length = (uint32_t)vl;

    buffer = new char[length + 1];

    value->GetBuffer(buffer, length);

    buffer[length] = 0;

    kvp = (float)atof(buffer);

    delete buffer;

    return true;
}