NMR probe for imaging small samples

An NMR imaging apparatus comprising:

• a conventional NMR imaging probe having a cylindrical probe body with an inner end and outer end and a cylindrical dewar channel positioned coaxially within the probe body and extending longitudinally therethrough;
• a first resonant circuit for delivering radio frequency energy to a sample and for gathering NMR signals generated thereby;
• the first resonant circuit including a removable coil, a first adjustable capacitor, and means for mounting the first resonant circuit on the probe inner end;
• a small-sample imaging apparatus interchangeable with the removable coil and comprising an elongate, cylindrical insert body having a first end, a second end and a diameter which allows the insert body to slide the through the dewar channel so that the first end extends to the probe body inner end;
• means for attaching the insert body second end into the probe body outer end;
• a small-sample imaging coil;
• a rigid stalk connected to the first end and to the small-sample imaging coil for mounting the small-sample imaging coil at a predetermined distance from the first end;
• a second adjustable capacitor physically mounted on the stalk at the predetermined distance from the first end and substantially adjacent to the small-sample imaging coil and electrically connected to the small-sample imaging coil to form a second resonant circuit so that substantially all inductance in the second resonant circuit arises from the sample imaging coil and substantially all the capacitance in the second resonant circuit arises from the second adjustable capacitor;
• a coaxial cable passing through the insert body and connected to the second resonant circuit for applying radio frequency energy to the second resonant circuit;
• and
• means passing through the insert body for manually adjusting the second adjustable capacitor.

A small-sample NMR imaging probe in combination with an NMR imaging system, the NMR imaging system employing a removable coil insert for use when a sample is equal to, or greater than, a predetermined size, the coil insert comprising a radio-frequency coil and a connector for connecting the coil to a first adjustable capacitor, the combination comprising:

• an imaging probe having a cylindrical probe body with an outer end and an inner end, the probe body having a hollow dewar channel extending longitudinally therethrough;
• first adjustable capacitor mounted on the probe body inner end;
• an elongate, cylindrical insert body for use when the sample is less than the predetermined size, the insert body having a first end and a diameter which allows the insert body to slide through the dewar channel so that the first end extends to the probe body inner end;
• a small-sample imaging coil;
• means for mounting the small-sample imaging coil at a predetermined distance from the first end;
• a second adjustable capacitor mounted in close proximity to the small-sample imaging coil and electrically connected to the small-sample imaging coil to form a resonant circuit so that substantially all the inductance in the circuit arises from the small-sample imaging coil and substantially all the capacitance in the resonant circuit arises from the second variable capacitor;
• and
• means for applying radio frequency energy to the resonant circuit.

An NMR imaging apparatus comprising:

• an NMR probe having a probe body with an inner end and an outer end and means for generating NMR images connected to the probe body;
• the means for generating NMR images including a first imaging coil and first variable capacitor;
• the means for generating NMR images further being interchangeable with a small-sample imaging apparatus;
• a small-sample imaging apparatus comprising;
• a) an insert body having a first end, the insert body being insertable into the probe body;
• b) means for attaching the insert body to the probe body outer end after the insert body has been inserted into the probe body;
• c) a second imaging coil;
• d) means for mounting the second imaging coil at a predetermined distance from the first insert body and;
• e) a second variable capacitor physically mounted sufficiently close to the second imaging coil and electrically connected to the second imaging coil to form a resonant circuit so that substantially all inductance in the resonant circuit arises from the second imaging coil and all the capacitance arises from the second variable capacitor;
• and
• f) means for applying radio frequency energy to the resonant circuit.