Nuclear Medicine Camera for Cardiac Imaging Buyers Guide

A cardiac focused nuclear medicine camera is a remarkable piece of equipment that can image the heart, help diagnose coronary artery disease, cardiomyopathy and many other heart conditions. While all cardiac-focused gamma cameras produce a similar type of image (SPECT study), they can vary significantly in their design, functionality, features, and cost. Whether it’s the number of detectors, the method by which they image patients, the maximum weight they can support, or the size of the imaging “sweet spot”, your best decision will be made by weighing the advantages and disadvantages of each model and manufacturer. This post explores three of the most popular nuclear medicine cardiac cameras and sees how they compare.

Nuclear Medicine Gamma Camera Manufacturers

Three of the most well-known gamma camera manufacturers used in cardiology include Digirad, Spectrum Dynamics, and GE. Each manufacturer uses a proprietary mix of hardware and software to produce the image. All of the three leaders in the nuclear medicine gamma camera market use solid-state technology. First developed by Digirad in 2000, solid-state imaging allows nuclear cameras to be smaller, requires less radiation to the patient, and enables a much faster image acquisition. Here is a basic overview of each nuclear medicine gamma camera from these providers:

Digirad

Nuclear medicine gamma cameras from Digirad include the Cardius 2 XPO, Cardius 3 XPO, and the X-ACT+. The Digirad cameras have two or three heads depending on the model and provide a 180° view of the heart. Unlike most manufacturers, the Digirad cameras image patients in an upright position rather than supine. The upright imaging allows for a clearer view of the heart due to a lack of unwanted artifacts in the image. Additionally, the Digirad X-ACT+ offers true, fully integrated micro-low dose fluorescence attenuation correction. This is the only gamma camera in this comparison that provides true attenuation correction.

Digirad cameras are also unique in that they leverage Cesium Iodide (CsI) for the crystal material. CsI is a scintillator with good stopping power for low-energy gamma rays, emits more optical photons than sodium iodide, and has lower manufacturing costs. CsI also allows for the same gamma-ray reaction as CZT, but the conversion is done indirectly using a photodiode. The Digirad line-up of Cardiac Cameras all feature an integrated computer processing station and support Windows 10 for maximum security and IT compliance. Digirad Nuclear Medicine Camera Overview:

• Cost Range: $185,000 – $397,000
• Patient Position: Upright
• Crystal Material: CsI/photodiode
• Average Cost of Service: $19,000 – $29,000 per year

Spectrum Dynamics

The D-SPECT Cardio Camera from Spectrum Dynamics is a cardiac-focused nuclear camera . The system uses “wobbling” detector columns to capture a SPECT image. The gantry design is counter-balanced to produce a smooth motion, and the camera uses electromagnetic brakes to lock the gantry positions. Much like the Digirad cameras, the D-SPECT models have a small footprint and an open gantry design, which reduces claustrophobia.

The camera can support patients up to 1,000 lbs and can be adjusted to image in a reclined or recumbent position. Due to the configuration and capabilities of this system, many cardiologists require their technologists to acquire two sets of stress images on this camera (reclined and recumbent) to ensure clinical accuracy and confidence. The D-SPECT detector technology comes with an option of six or nine detectors and relies on a pre-defined target area for imaging and is not customized for the patient. Some technologists have experienced image truncation on patients whose heart position is not within the sweet spot. Cameras from Spectrum Dynamics rely on CZT detector technology which can have higher costs and makes true attenuation correction harder to perform. Spectrum Dynamics D-SPECT Camera Overview:

• Cost Range: $325,000 – $500,000
• Patient Position: Variable System (Reclined or Recumbent)
• Crystal Material: CZT
• Average Cost of Service: $32,000 – $36,000 per year

GE Discovery NM530c

The GE Discovery NM530c is a CZT-based nuclear medicine camera with Alcyone technology. According to GE, the camera can perform a scan in three minutes and offers the ability for reduced dose imaging at longer times. The camera uses a stationary design where the patient stays still and the high efficiency, multiple pinhole detectors oscillate around them. The GE NM 530c does not offer true attenuation correction and recommends imaging patients in both a supine and prone position to create attenuation shift and identify artifacts.

Alcyone technology is unique to GE, and according to the product literature, it provides a four-fold increase in sensitivity. The patient weight capacity of the NM530c is listed at 440 lbs. Similar to the Spectrum Dynamics D-SPECT camera, the NM530c focuses on a “sweet spot”, which may limit the region of interest imaged and increase the risk of image truncation. GE Discover NM530c Camera Overview:

• Cost Range: $385,000 – $400,000
• Patient Position: Supine and Prone
• Crystal Material: CZT
• Average Cost of Service: $38,000 to $40,000 per year

Considerations when Choosing a Nuclear Medicine Gamma Camera

Sweet Spot Imaging vs. Cardiocentric Imaging

The way the camera captures the image has a direct impact on the overall quality of your study. The GE NM530 and D-SPECT cameras have a fixed range that focuses on a “sweet spot” for the best image quality. For most patients, this works well, but there are common cases where the heart cannot be placed within the target area, thereby increasing the risk of truncation (where the image of the heart, or region of interest, is not centered in the field of view). The reasons for this include patients that are too large, overall obesity, or patients who are very small. The Digirad X-ACT+ and Cardius Series cameras are able to adjust the target image area and better position the heart within the field of view.

CsI vs. CZT

The crystal material and conversion method may seem like an odd feature to consider when evaluating cardiac gamma cameras, but it affects the price and quality of your machine. CZT works by direct conversion, while CsI uses indirect conversion using photodiodes. One of the major differences is the cost of the materials involved for doing this. CZT is significantly more expensive to produce than CsI. There are claims that CZT is ten times more sensitive than NaI/PMT. However, in actual practice, a CZT camera’s photopeak detection efficiency is only 64% of either NaI/PMT or CsI/Photodiode. This poor intrinsic peak efficiency is due to a common problem in direct conversion solid-state detectors called hole tailing. The resulting loss of sensitivity means that the energy window must be set wider than necessary for the specified energy resolution to recover the lost photopeak counts. Additionally, there is no improvement in scatter rejection with CZT, resulting in higher costs and reduced precision. By comparison, CsI doesn’t suffer from hole tailing as the conversion is indirect.

Attenuation Correction

Attenuation correction is a mechanism that removes soft tissue artifacts from nuclear images. The goal is to reduce the impact of attenuation in order to provide images that are more uniform and allow for higher reading confidence. Through advancements in solid-state technology and attenuation correction methods, specifically Fluoresce Attenuation Correction (FAC), SPECT can now deliver higher quality, PET-like image resolution, greater diagnostic accuracy, and higher reading confidence than ever before. Fluorescence attenuation correction is available in conjunction with the Digirad X-ACT+ camera. The X-ACT+ is the only SPECT/FAC MPI system that features a combination of solid-state detectors, rapid imaging detector geometry, and low-dose fluorescence x-ray attenuation correction. Other SPECT manufacturers have claimed their cameras offer Attenuation Correction, but many of these “features” are simply software algorithms and post-processing enhancements that emulate Attenuation Correction. Without CT or a fluorescence X-ray, you simply cannot have true Attenuation Correction.

Which Nuclear Medicine Gamma Camera is the Best?

All three of the nuclear medicine cameras listed in this post are excellent pieces of equipment that provide state-of-the-art SPECT imaging. The quality of the solid-state technology in each of these cameras far exceeds older Anger technology that relied on vacuum tube photomultipliers. The chart below summarizes the key differences between the three cameras listed in this post.

Ultimately the choice comes down to a mix of price, features, availability, and finding a company you are comfortable working with. Most SPECT cameras are used for 8+ years, so the decision is one you and your patients will experience for years to come. If you are interested in learning more about the X-ACT+ from Digirad or have questions about the information covered in this post, feel free to contact the Digirad team.