Nuclear Medicine Resources Manual

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One example is the choice of a dual detector system rather than a single

detector system.

4.2.2. Contractual considerations

When purchasing an imaging system it is imperative that a document be

prepared that not only defines the requirements of the system to be purchased

but also clearly outlines the obligations placed on both the supplier and the

receiving institution.

A list of the required specifications of the imaging system is very

important. In addition to the specification sheets made available by the vendors,

the user should also consider the main studies to be performed on the camera

and the specifications necessary to obtain optimal clinical results.

Complete operation and service manuals should be supplied with the

gamma camera and should remain the property of the user. Appropriate

radiation sources and phantoms needed for quality control tests should be

purchased at the time of instrument acquisition. Software should be available to

quantify quality control results.

Bids should clearly define the instrument’s performance specifications,

referring to the results of NEMA tests. Results of acceptance tests, performed

immediately after installation, will be compared with these data. Most

acceptance tests should be performed by the supplier, under the supervision of,

and in cooperation with, a suitably experienced nuclear medicine physicist. All

phantoms and test equipment required for acceptance testing should be made

available free of charge by the supplier. A percentage of the purchase price (e.g.

20%) should be held back until the user is satisfied with the acceptance test

results. A clause built into the purchase agreement should specify the

procedures to be used during acceptance testing, minimum acceptable results

and actions to be taken if acceptance test results do not meet pre-purchase

agreements.

Training of personnel should be included in the company bid. Training on

the operation and programming of the system, including acquisition and

processing of patient studies, must be supplied. Furthermore, training on the

operating system and computer maintenance (e.g. the steps required to reload

software) must also be included.

It should be emphasized that the full installation, including acceptance

testing and on-site training, is the responsibility of the supplier. A competent

service person from the company, with training on the specified equipment,

should be available.

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The contract should state clearly which spare parts are available locally

and the supplier’s response time to supply those spare parts that are not

available locally.

4.2.3. Site preparation and installation

Before installation takes place, steps should be taken to ensure that the

environment is suitable for the installation. These will include the following:

(a)

The room should be of an appropriate size and in an acceptable condition

before installation takes place. Particular care should be taken to ensure

that the floor is sufficiently robust to support the equipment. Floor loading

details are provided in the supplier’s specification, and local engineering

staff should be consulted.

(b) The electric power supply should be stable; if not, a constant voltage

transformer should be installed. An uninterrupted power supply system is

essential for optimal utilization of the gamma camera system. The

grounding of the equipment should be checked since this can be a source

of electrical noise as well as being a potential hazard. Poor quality electric

supply is recognized as a major reason for instrument malfunction and

failure.

levels in the vicinity of the equipment are not markedly influenced by the

location of the radiopharmacy, the storage and movement of radioactive

materials and the movement of patients incorporating these materials.

Similarly, care should be taken that other radiation sources in the vicinity

(X ray machines, linear accelerators or

Co devices) do not contribute to

the background.

(d) The presence of a strong magnetic field in the vicinity may also influence

the functioning of the gamma camera. If there is an MRI system in the

same institution, the magnetic field levels should be monitored.

(e) Air-conditioning units with properly deflected airstreams and dehumidi-

fiers should be provided and used permanently to provide continuous

protection against the adverse effects of temperature changes and

humidity.

(f) Instruments should not be installed where they could be exposed to dust,

smoke or chemical fumes.

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4.2.4. Acceptance tests

The first crucial step after installation of the imaging equipment is the

initial evaluation or acceptance testing. This includes not only confirmation that

the instrument performs according to specifications, but also evaluation of

performance under conditions that will be encountered in clinical practice.

These tests should be carried out immediately after installation. The user

should not accept an instrument that fails to conform to specifications. No

instrument should be put into routine use unless it has been shown through

acceptance testing to be performing optimally. Provided the equipment is

operating according to specification and has been demonstrated to be safe, a

limited number of patient studies should be performed as part of the acceptance

procedure.

Acceptance tests require special test devices, phantoms and evaluation

software. Quantification of tests is essential in order to compare results with

specifications and to provide baseline values for future comparison. Therefore it

is recommended that the specialized instruments and software are provided by

the company for the purpose of acceptance testing, and that the tests are carried

out on-site by the company engineer, under supervision of the user. The user

may chose to perform additional tests to confirm the operation of the

equipment and may chose to use these results as a reference for future quality

control. If necessary, the user should invite a competent expert to participate in

the acceptance tests and the evaluation of the results.

4.2.5. Warranty period

The warranty period (usually one year) should be clearly defined in the

purchasing documents. The warranty period is very useful in exposing possible

failures of electronic components at an early stage. The manufacturer has an

obligation to repair the problem at no cost to the user. It is recommended that

the warranty period should start only when the equipment has passed all

acceptance tests. Equipment should be put into clinical use as soon as possible in

order to optimize the warranty period.

There must be a clear understanding between the supplier and the end

user as to how the warranty period will be influenced if a major part of the

system needs to be replaced during the warranty period. The company should

perform regular services and preventative maintenance procedures during this

period.

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4.2.6. Service contracts

A service contract should be negotiated, to include labour and either no

spare parts, spare parts excluding the crystal, or all spare parts. The availability

of spare parts and the terms of payment should be stated. The price of the

service contract usually varies between 2 and 10% of the purchase price of the

imaging system.

The supplier should make available a qualified person to perform prevent-

ative maintenance and servicing on the camera (proof of adequate training

should be provided). In the event of system failure, the maximum response time

of the service engineer should be specified (two hours is a typical figure). The

maximum acceptable downtime per year should also be specified (10% of

available working days is suggested). A penalty clause should be added to the

contract if the supplier does not meet all the requirements.

The supplier should supply a checklist of what will be performed during

the services for preventative maintenance. This checklist should be compiled to

the satisfaction of the user. The service engineer should leave on-site a record of

all tests and checks performed.

It is recommended that quality control tests such as those for uniformity

and spatial resolution be performed before each service and repeated after

completion, to evaluate the effectiveness of the service.

4.3. SINGLE PHOTON IMAGING

4.3.1. General considerations

The main imaging device in nuclear medicine is the gamma camera based

on a sodium iodide detector, developed originally in 1958 by H. Anger.

Although there are rectilinear scanners still in use, these will not be discussed.

Similarly, while there continue to be various experimental detectors (e.g. solid

state detectors) that may have particular appeal for specialized applications (e.g.

breast imaging), their current limited use does not warrant their inclusion. The

conventional gamma camera forms the basis of systems used for solely planar

imaging and with appropriate mounting on a rotating gantry is used for SPECT.

Multidetector systems are normally constructed using multiple gamma cameras

that improve the efficiency of detection. Designs using multiple small detectors

rather than conventional gamma cameras are also not in widespread use. The

addition of coincidence circuitry to the conventional dual head gamma camera

allows it to be used for ‘positron imaging’ as discussed in a later section of this

manual. To a large extent the versatility of the conventional gamma camera is a

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particular strength. The design of gamma cameras has improved dramatically

over a long period, with current devices being very much digital systems rather

than simply being interfaced to an acquisition computer. Over the years the

performance of cameras has also improved; not only is their resolution,

uniformity and count rate capability better but also, more importantly, their

stability is improved. Sensitivity remains a constraint of the collimated detection

geometry.

Although there have been various attempts to design specialized gamma

camera systems for specific applications, in general the more successful designs

are those that provide flexibility. In many centres, the camera is required for

different applications and, at the time of purchase, it is often difficult to predict

what the ultimate application may be. A system that permits efficient SPECT

acquisition without compromising the utility for planar imaging is particularly

attractive. Provided this flexibility is maintained, a dual head system has the

advantage of improved throughput, and the low likelihood of both heads having

problems means that a single head can be available for continued operation,

even when the second head is non-functioning. A dual head system also offers

the possibility for dual photon imaging, as discussed elsewhere. It is this

flexibility that has resulted in the dual head camera currently being the most

popular system. Although more expensive than a single head system, the dual

head system is cost effective in terms of both throughput and flexibility.

The computer is now an integral part of any imaging system, and

consideration of not only speed but also the range of available software,

connectivity and ease of upgrade become important considerations. There has

been a trend in recent years towards standard computer platforms that can keep

abreast of developments more easily than the older manufacturer-specific

systems. Even though these systems tend to lag behind the general release of

systems software, they generally offer a wide range of available peripherals and

general software (including free software). Although there is a wide selection of

advanced clinical applications software, the ability to develop user defined

applications, without the need for advanced programming skills, remains a

requirement that is not always available. Confirmation of results arising from

application software is the responsibility of the site concerned. Particular care

needs to be taken to ensure that interpretation is correct for the population

concerned (e.g. normal databases derived from specific populations may be

inappropriate). Software phantoms, i.e. reference data sets that can be used to

check the accuracy of analysis, are available via the Internet.

There are many accessories for gamma cameras, including some that

reduce overall reliability. One example is automated collimator exchangers that

do not permit manual override and therefore result in the system being

inoperable in the event of malfunction. Collimators continue to be vital

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components of single photon imaging. Although basic collimators have changed

very little (except for construction), there is a range of specialized collimators

now available including fanbeam and cone-beam collimators that provide

improved efficiency as well as marginally improved resolution compared with

that of parallel hole collimators. Some manufacturers strive for ‘super-

resolution’ at the expense of counting efficiency; consequently specifications

should be carefully examined as collimator names can be misleading. For

cardiac SPECT applications, there are several accessories that are desirable,

such as some form of transmission measurement to permit attenuation

correction in the thorax and an electrocardiogram (ECG) with a suitable trigger

pulse used for gated acquisition. In the case of transmission sources, there is a

range of available options with no single system acknowledged as clearly

superior, and effectiveness of correction is dependent to some extent on the

software supplied. For example, it is now common for manufacturers to offer

iterative reconstruction software as an alternative to filtered back-projection.

The system choice is normally based on the underlying camera unless there is

very high priority for a specific acquisition (e.g. cardiac SPECT).

4.3.2. Specifications

The tender specification list must include the items listed below. A more

detailed questionnaire, aimed at manufacturers, is available. The use of such an

approach enables comparison of bids, resulting in a possible scoring system that

will assist in the decision making process.

(a)

Gamma camera and accessories:

—

Detector performance;

— Detector head and gantry design;

—Detector head motion;

—Collimators;

—Pulse height analysis;

—Imaging table(s) and attachments.

(b) Data acquisition:

—

General acquisition features;

—Static acquisition;

—Dynamic acquisition;

—List mode acquisition;

—Gated cardiac acquisition;

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—Whole body imaging;

—Automatic patient–detector distance sensing;

—Tomography.

—

Data display;

—Image manipulation and arithmetic;

— Region of interest (ROI) generation and display;

— Curve generation, display and arithmetic;

—Processing of SPECT data;

—File and disk utilities;

— Data transfer;

—Archiving and backup;

— Quality control software and test data;

— Patient database management software;

—Software development tools;

—Network capability;

—Multi-tasking capability (ability to acquire and process simultaneously);

—Clinical software;

— Data security.

(d) Accessories:

—

Hard copy;

—Physiological triggering;

—Anatomical landmarking;

—Phantoms:

Co, bar and SPECT.

(e) General:

—

Warranty, maintenance and reliability;

— Room layout;

—Pre-installation work and requirements;

—Purchase, installation and training;

—Electrical and mechanical safety;

— Quality management systems;

—Documentation.

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(f) Multidetector gamma camera systems:

—

Performance requirements;

—Detector head motion;

—Detector performance assessment by comparison of the NEMA

performance parameters from the various manufacturers.

4.3.3. Acceptance tests

4.3.3.1. List of acceptance tests for planar or SPECT gamma cameras

(a)

Intrinsic NEMA procedures:

—

Energy resolution;

— Flood field uniformity;

—Spatial resolution;

— Spatial linearity;

—Count rate performance and maximum count rate;

—Multiple window spatial registration.

(b) Extrinsic (system) NEMA procedures:

—

Flood field uniformity;

—Spatial resolution with and without scatter;

—Sensitivity for each collimator;

—Detector head shielding leakage.

—

SPECT centre of rotation;

— Angular linearity errors;

—Uniformity;

—Tomographic slice uniformity;

—Rotational uniformity;

—System volume sensitivity (NEMA);

—Tomographic resolution:

●

tomographic resolution in air (NEMA),

●

tomographic resolution in a scatter medium (NEMA),

●

test of slice thickness (IAEA),

●

total performance check (data spectrum phantom) (American

Association of Physicists in Medicine (AAPM)),

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●

tomographic uniformity,

●

tomographic resolution (spheres and rods),

●

contrast.

The above tests should be done in addition to the following planar gamma

camera tests.

(d) Specific tests for multiple detector systems:

—

Multiple detector registration;

—Matched sensitivity;

— Matched pixel calibration;

— Matched centre of rotation (COR).

4.3.3.2. Minimum quality control requirements for gamma cameras

Routine quality control is an essential requirement for any nuclear

medicine practice in order to ensure that equipment operation remains optimal.

Quality control is commonly, but wrongly, viewed as a difficult and time

consuming chore and, for this reason, is frequently neglected. This section

provides guidelines for minimum quality control based on the Australian and

New Zealand Society of Nuclear Medicine recommendations and is compatible

with other recommendations. The guidelines are intended to provide a very

basic practical approach to gamma camera quality control, requiring very little

specialized equipment or expertise. It is therefore recommended that these

guidelines be adopted by all nuclear medicine practices. The minimum quality

control tests are intended to detect problems before they have an impact on

clinical patient studies. They are not intended to provide a full evaluation of

equipment performance. Further tests may be required to trace the cause of a

problem and to ensure that the equipment is performing properly after service

or adjustment. Exact quality control procedures vary between manufacturers

and models, making it impractical to provide detailed quality control procedures

covering all equipment.

In order to make quality control procedures as simple as possible, the

following is a suggested list of the minimum test equipment required:

(a)

Cobalt-57 sheet source

This source is recommended for high count extrinsic uniformity checks

and the collection of uniformity correction floods. It is preferable to water filled

flood tanks, which may introduce non-uniformities due to poor mixing, bulging

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119

and air bubbles, although care needs to be taken with new sources. On some

systems, a water filled flood tank may also be required to calibrate the system

for non-

99m

Tc radionuclides such as

Ga.

(b) Resolution phantom

A four quadrant resolution phantom is recommended. The finest bars

should be small enough to test the intrinsic resolution of the system (i.e. 2–

2.2

mm bar width) and the largest bar should allow some extrinsic tests to be

carried out (i.e. 4.5–4.8 mm bar width).

On some cameras, special jigs are required for calibrating COR offset and

other calibration procedures.

It is imperative that quality control procedures be carried out in a

consistent manner (i.e. the same collimator, orientation, activity and energy

window) and that qality control results and settings be recorded. Proper record

keeping greatly facilitates detection of gradual deterioration of performance

over an extended period of time. A baseline set of quality results should be

recorded after installation and acceptance testing to serve as a reference.

Quality control procedures for SPECT cameras in general are more

stringent than those for planar cameras. Since corrections can be applied to

SPECT data such as uniformity and COR offsets, it is more important that the

quality control parameters are stable over time, rather than having an exact

absolute value.

For each quality control test listed below, the aims and rationale are

described first, followed by a general procedure for performing the test.

Although recommendations are made on the frequency of the quality control

tests, it must be pointed out that in some tests this depends on the equipment. It

is recommended that, on the basis of these guidelines, an experienced nuclear

medicine physicist draw up detailed quality control protocols for use with

specific equipment.

In practice, the routine quality control tests should give data that permit

the physician to decide whether:

—

To image patients normally;

—To image patients but request that the equipment be serviced;

—To cease patient studies until the system is repaired.