Approaches to Dose Reduction in Molecular Imaging

Approaches to Dose Reduction in Molecular Imaging

Dose Reduction Technology for SPECT

SPECT•CT imaging procedures are categorized into four main clinical areas – cardiology, oncology, general purpose imaging, and neurology. Minimizing dose is equally important in all clinical segments, but – unlik e CT or MRI – h ybrid imaging in nuclear medicine (SPECT•CT and PET•CT), permits dose to be optimized in two ways: by reducing the dose of the injected radiopharmaceutical and by minimizing the CT dose emitted from the hybrid scanner. While pressure is increasing to minimize the CT dose, it is also critically important to reduce the injected dose in SPECT imaging to help the physician improve patient safety.

Additionally, but no less importantly, there are only five nuclear reactors worldwide that produce 100% of the most commonly used SPECT tracer – technetium (99mTc). Some of these reactors have been shut down for temporary maintenance, and the availability of 99mTc, consequently, has been reduced worldwide. This limited availability has brought a need for more efficient use of technetium. Therefore, injecting less dose per patient is very important so that hospitals can continue to scan their full patient load.

Siemens SymbiaTM SPECT·CT product line is pioneering dose savings in both SPECT and CT. Not only does Siemens have the most integrated diagnostic SPECT·CT systems, but also provides features that can save up to 75% of the dose while maintaining image quality. The following sections provide a short overview of the dose-saving features of Symbia.

Features pioneered by Siemens to reduce dose in Symbia SPECT·CT include (Figure 1).

AUTOFORM Collimators

Conventional collimators have uneven septa wall thickness, which decreases sensitivity and increases the dose or scan time needed to acquire a valuable image.

Siemens is the only equipment manufacturer that designs and produces its collimators inhouse. AUTOFORM collimators use a proprietary design that provides uniform septa wall thickness. The proprietary collimator design offers the industry’s highest sensitivity,1 with up to 26% more counts1, while maintaining image resolution.

Siemens AUTOFORM collimators offer the highest SPECT LEHR sensitivity in the market today that enables: 

  1. Up-to 26% lower injected dose
  2. Up-to 26% faster imaging


1 Based on competitive literature available at time of publication. Data on file.

Flash 3D Iterative Reconstruction

Inaccurate image reconstruction impacts image quality and can result in both false positives and false negatives. Most reconstructed images are created using algorithms that do not account for the physical characteristics of the image acquisition system.

Symbia SPECT•CT scanners with Flash reconstruction use a measured 3D collimator beam model in the iteration process. Correct modeling of the collimator distributes the activity over the slices for more accurate reconstruction. With Flash, the spatial resolution of the collimator is modeled to maintain the precise shape of the lesion. As a result, images are reconstructed with more counts in the correct volume, increasing image contrast.

Flash enables up-to 45% higher reconstructed resolution according to NEMA specifications1 that ultimately enables:

  1. Up-to 50% less injected dose
  2. Up-to 50% faster imaging


1 Based on competitive literature available at time of publication. Data on file.


Automatic Quality Control

Scanners require regular quality control (QC) tests to validate calibration of the detectors. For conventional scanners, quality control is performed manually, and typically requires 20 minutes to an hour for daily QC, and about six hours for monthly QC. Because the tests require preparation and handling of open radioactive sources, the process must be rotated among the staff to avoid overexposure. Dose spillage adds further risk to the process.

With Siemens AQC, the process is performed automatically overnight, with a report provided for the technologist to review the next morning. Siemens AQC facilitates performance trending, eliminates the risk of open-source spillage and reduces staff radiation exposure. 

The benefits of Automatic Quality Control (AQC) include:

  • Reliable, consistently reproducible QC
  • Eliminated risk of spillage with open sources
  • Operator dose reduction
  • Can run automatically overnight saving time for the operator 


Routine cardiac studies can take up to 20 minutes, limiting the number of patient scans. To achieve the desired image quality, patients are often injected with high doses that increase radiation exposure.
Siemens IQ•SPECT is the only technology that performs ultra-fast cardiac imaging with a general purpose camera. Its unique collimator design, cardio-centric image acquisition and advanced reconstruction technology acquires four-times more counts than conventional methods for the highest quality images independent of age, body shape or size.

With IQ•SPECT, physicians can perform a myocardial perfusion imaging study in on of the following protocols options:

  1. Up-to 75% less injected dose in 16 minutes
  2. Up-to 50% less injected dose in 8 minutes
  3. Up-to 25% less injected dose in 4 minutes

Low-Dose CT AC

In hybrid imaging one of the most commonly used CT protocols is attenuation correction. Highend SPECT/CT scanners that incorporate CT systems with a higher number of slices may require more energy, potentially exposing the patient to higher levels of radiation. Additionally, conventional SPECT/CT scanners do not allow selection of lower X-ray tube voltages for attenuation correction scans.

Siemens high-end 16-slice CT system delivers up to 74% less radiation1 to the patient during attenuation correction and the user can adjust X-ray tube voltages to further reduce dose exposure. For the three most common nuclear medicine attenuation correction procedures, Siemens CT technology delivers the lowest dose compared to conventional scanners.


1 Based on competitive literature available at time of publication. Data on file. Dose values compared are based upon factory default protocols from GE NM670.